Symposium 344 - Poster Abstracts


A Multi-Phase Gas Description and its Implications for Numerical Models of Dwarf Galaxies

Kühtreiber, Matthias

We present results from our N-body/SPH code “cd-sph” including a modern state-of-the-art SPH algorithm and a multi-phase description of the interstellar medium (ISM). This approach aims at overcoming various issues of a single gas phase used in most hydrodynamical simulations. The ISM is modelled more realistically  by adding a cold cloudy medium to the hot/warm gas represented by SPH particles. These clouds are treated with the sticky-particle method and allow for coagulation and fragmentation of molecular clouds. The formation of stars is realized by directly applying the Jeans criterion to the clouds. Stars, which are treated as collisionless N-body particles, and the gas phases are mutually coupled by mass, momentum, and energy exchange in a self-consistent manner.Different feedback processes from stars are taken into account distributing energy, mass and newly produced chemical elements to the cold clouds or to the hot/warm medium. Depending on the stellar mass, UV radiation, stellar winds supernovae type II, type Ia and planetary nebulae, are considered. The different gas phases are not decoupled from each other, as they can exchange mass, including chemical elements and energy through thermal conduction, leading to condensation or evaporation. Due to their different dynamical properties, additional drag forces are included which lead to momentum exchange between clouds and the gaseous medium.We apply our model to isolated dwarf galaxies in order to investigate their chemo-dynamical evolution and make comparisons with observations and with single-phase simulations. Thereby, we demonstrate the differences of the dynamics and chemical evolution due to the multi phase ISM and the stellar feedback processes which affect the clouds and the hot/warm medium in a decoupled manner. We further discuss mass loading as an important process for the chemo-dynamical evolution in dwarf galaxies and implications for simulations of ram pressure stripping and galaxy harassment.

FOSSILs in the Galactic Halo

Grillmair, Carl

We use a matched filter to detect compact groups of old, metal-poor stars that we term FOSSILs (Fragments of Old Stellar Systems In Limbo). With size scales on the order of 10 arcminutes, distances ranging from 2 to 200 kpc, and memberships ranging from a handful to several dozen stars, these FOSSILs stand out from the surrounding field and are presumably signatures of, or debris from, ancient star clusters and dwarf galaxies. They may be localized concentrations of stars within more extensive tidal streams, and in several cases may be the signatures of extant but heretofore undetected ultrafaint galaxies. Using magnitudes and colors from the Pan-STARRs survey, we detect 140 such FOSSILs at 5σ or greater in a 2200 square degree region in the vicinity of the north Galactic pole. Spectroscopic and astrometric follow-up of these FOSSILs will be required to determine the nature of these structures, deepen our understanding of the make-up and accretion history of the Galactic halo, and perhaps alleviate the missing satellites problem.

Observing high-redshift dwarf galaxies with JWST

Stiavelli, Massimo

We have carried out high resolution numerical simulation to study the formation of pristine and metal poor galaxies before the reionization era in order to make observability predictions for the James Webb Space Telescope.

Tidal interactions shaping dwarf galaxies

Lee-Waddell, Karen

Dwarf galaxies are easily shaped by the influence of neighbouring systems. Accordingly, these low-mass objects can be used to probe the dynamical processes that are affecting the environments in which they are contained._x000D_ I will present observational data of an assortment of dwarf galaxies that are being formed and/or evolved by tidal forces. The neutral hydrogen gas and stellar content of these galaxies enable a more complete interpretation of the internal dynamics. In most cases, the multi-wavelength datasets coalesce on a common evolutionary history; however, there are a few objects for which the data appear almost contradictory.

Rotating stellar populations and morphology analysis in dSph galaxies, possible hints to understand their formation and evolution.

Jara, Alex

According to the Lambda-CDM cosmological model, dwarf spheroidal (dSph) galaxies are the basic building blocks for the formation of bigger structures, because of their high velocity dispersions and low luminosities, they are thought to be the most dark matter (DM) dominated objects in the universe. There are several models that attempt to explain their formation and evolution invoking two body interactions, e.g., resonant stripping or tidal stirring, but they have difficulty explaining the formation of isolated dSph galaxies. Another formation scenario is the dissolving star cluster model (Assmann et al. 2013, Alarcon et al. 2017), according to this model dSph galaxies were formed by the fusion and dissolution of several star clusters (SCs) formed in a giant molecular gas cloud within a DM halo. Simmulations predict kinematic substructures formed by stars following similar orbits and clumps of stars formed for star cluster which were not entirely dissolved. In this work we will compare simulations of the dissolving star cluster model with observational data.

The blue compact dwarf galaxies in MaNGA

Yin, Jun

The nature of possible evolutionary pathways between various types of dwarf galaxies is still not fully understood.Blue compact dwarf galaxies (BCDs) provide a unique window into dwarf galaxy formation and evolution and are often thought of as an evolutionary stage between different classes of dwarf galaxies. In this study we selected a BCDs sample from MaNGA MPL-6, and seperated the starburst (SB) components from the underlying hosts of BCDs via the 2D spectrum. We want to compare our results to the previous photometry-based studies, and investigate the connections between the SB components and the hosts, the structural differences between different types of dwarf galaxies.

Dwarf Galaxies in the Local Volume

Karachentsev, Igor

A catalog of 1060 Local volume (=LV) galaxies situated within a distance of 11 Mpc contains 870 dwarfs, i.e. 5/6 of the sample. Almost 40% of them have accurate distances measured with Hubble Space Telescope. Most of the LV dwarfs have been observed already in HI and H_alpha emission lines, as well in far-ultraviolet with GALEX. We present basic properties of the LV dwarfs, their HI-mass content and star-formation rate in different local environments. We discuss a baryonic Tully-Fisher relation for the LV dwarfs, and apply it to determine TF-distances for several hundreds other local galaxies. The accurate distances and radial velocities of the LV dwarfs are used by us to trace dark matter distribution within 11 Mpc. We discuss also does the Local Group may be treated as a typical or uncommon representative of the LV population.

Influence of the void environment on chemical abundances in dwarf galaxies and implications for connecting star formation and halo mass

Douglass, Kelly

We study how the void environment affects the chemical evolution of galaxies in the universe by comparing the oxygen and nitrogen abundances of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate the oxygen, nitrogen, and neon abundances of 887 void dwarf galaxies and 666 dwarf galaxies in denser regions. We use the Direct Te method for calculating the gas-phase chemical abundances in the dwarf galaxies because it is best suited for low metallicity, low mass (dwarf) galaxies. A substitute for the [O II] λ3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the Direct Te method. We find that void dwarf galaxies have slightly higher oxygen and neon abundances than dwarf galaxies in denser environments. The opposite trend is seen in both the nitrogen abundance and N/O ratio: void dwarf galaxies have slightly lower nitrogen abundances and lower N/O ratios than dwarf galaxies in denser regions. Our mass-N/O relationship shows that the secondary production of nitrogen commences at a lower stellar mass in void dwarf star-forming galaxies than in dwarf star-forming galaxies in denser environments. We also find that star-forming void dwarf galaxies have higher HI masses than the star-forming dwarf galaxies in denser regions. The lower N/O ratios and smaller stellar mass for secondary nitrogen production seen in void dwarf galaxies may indicate both delayed star formation as predicted by ΛCDM cosmology and a dependence of cosmic downsizing on the large-scale environment. The shift toward higher oxygen abundances and higher HI masses in void dwarf galaxies might be evidence of larger ratios of dark matter halo mass to stellar mass in voids than in denser regions.

Stellar properties of dwarf galaxies and their connections with the Milky Way halo

Revaz, Yves

In this talk, relying on recent cosmological zoom-in chemo-dynamical simulations, I will describe the stellar properties of 27 dwarf galaxies emerging from a LCDM framework. In this context, I will show how, in addition to the galaxy global properties, the model galaxy_x000D_ velocity dispersion profiles, half-light radii, star formation histories, metallicity distributions, and [Mg/Fe] abundance ratios fit the observations with a level of details never achieved before. The formation and sustainability of the metallicity gradients and kinetically distinct stellar populations will also be discussed._x000D_ Those new models demonstrate that there is no missing satellite problem. In addition, they show that the majority of dwarf galaxies do not necessary require a strong interaction with a host Milky Way like galaxy._x000D_ However, dwarf galaxies with complex star formation histories like Carina and Fornax are much more difficult to reproduce. Those systems are often believed to result from an interaction with the Milky Way. I will show that when such interaction is taken into account in our high resolution simulations through ram pressure stripping, a much more complex reality appears.

Supernova remnants in dwarf elliptical galaxy NGC185

Vucetic, Milica

In this paper we present our optical observations of NGC185 galaxy, which aimed to retrieve final status of supernova remnants (SNRs) in this dwarf elliptical companion of Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our recent deep photometric study through narrow-band Hα, [SII] and continuum filters has revealed complex structure of the interstellar medium in the center of the galaxy, also proposing that there could be more than one SNR. In order to confirm the SNR origin and study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6-m telescope at Special Astrophysical Observatory of the Russian Academy of Science, both in low (FWHM~500 km/s) and high (FWHM~120 km/s) resolution modes. We revealed the enhanced [SII]/Hα and [NII]/Hα line ratios, as well as high expansion velocities of the observed nebulae, indicating their nature as SNRs.

Dwarfs in the entourage of the Local Volume groups: flow tracers and cosmological probes

Kashibadze, Olga

We consider a sample of field dwarf galaxies with accurate distances and radial velocities around 14 massive groups in the Local Volume (LV). We combine all the data into a single synthetic LV group, and then determine its radius of the zero-velocity surface, which separates any overdensity against the global cosmic expansion. Our approach is based on a comparison of the observational data with the velocity field expected from the spherical infall model, including effects of the cosmological constant. We found the optimal value of the radius to be 0.93±0.02 Mpc. Assuming the standard Planck model parameters, it corresponds to the total mass of the synthetic group ~(1.6±0.2)×1012 M☉ Thus, we are faced with the paradoxical result that the total mass of the LV group estimated on the scale of 3-4 its virial radius is only 60% of the virial mass estimate. Anyway, we conclude that wide outskirts of the nearby groups do not contain a large amount of hidden mass outside their virial radius.

Dwarf galaxies: evidence of differential tidal effects in the Large Magellanic Cloud

Piatti, Andrés E.

We used DECam images to build for the first time stellar density and/or surface brightness radial profiles for almost all known ancient Large Magellanic Cloud (LMC) globular clusters (GCs). These are the most extended radial profiles built for these GCs so far. The studied GCs located farther than ~ 5 kpc from the LMC centre would not seem to present any hint of extended stellar structures, like the family of different features seen in an important number of Milky Way old GCs. The apparent negative detection of such outer region structural tracers could suggest that the LMC potential has not been efficient in stripping stars off its GCs. Those GCs located closer than ~ 5 kpc from the LMC centre show an excess of stars distributed in the outermost regions with respect to the nominal amount of stars predicted by the best-fitting empirical King models. Such an excess of stars tightly depends on the position of the GCs in the galaxy, in such a way that the closer the GC to the LMC centre, the larger the excess of stars. In addition, the GC radii also show a remarkable trend with the position of the GC in the LMC disc, namely: the farther the GC, the larger the GC radius. These outcomes can be fully interpreted in the light of the known GC radial velocity disc-like kinematics, from which GCs have been somehow mostly experiencing the influence of the LMC gravitational field at their respective mean distances from the LMC centre. The different dimensions of the analysed GCs do not seem to be related to any systematic difference in their masses. Despite this, GCs with deprojected distances smaller than ~ 5 kpc have lived for many more median relaxation times. This behaviour might also be a result of the stronger tidal fields, which have made the GCs dynamically evolved faster by bringing stars towards the outermost GC regions sooner than what would have been expected in an scenario of isolated two-body relaxation.

Hot star wind mass-loss rate predictions at low metallicity

Krticka, Jirí

Hot star winds are driven by the radiative force due to the light absorption in the lines of heavier elements. Therefore, the amount of mass lost by the star per unit of time, i.e., the mass-loss rate, is sensitive to the metallicity. Consequently, the hot star feedback mediated by the winds also depends on metallicity. We provide mass-loss rate predictions for O stars with low mass fraction of heavier elements Z < Zsun. Our predictions are based on global (unified, hydrodynamic) model atmospheres. The models allow us to predict wind terminal velocity and the mass-loss rate just from basic global stellar parameters. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity as Z^0.59. The predicted mass-loss rates agree with mass-loss rates derived from ultraviolet wind line profiles. We show that the rotational mixing affects the wind mass-loss rates at low metallicity. We study the influence of magnetic line blanketing, which might be important for binary black hole progenitors. Our models provide consistent mass-loss rate determinations, which can be used for quantitative study of stars at low metallicity.

Chemical abundances of Gaia-ESO metal-poor stars compared to stars in dwarf galaxies

Smiljanic, Rodolfo

Some of the Galactic metal-poor stars likely originate from stellar systems that have been accreted by the Milky Way. These systems include dwarf spheroidal galaxies. It has been shown in the past that stars in these systems can have distinct [alpha/Fe] vs [Fe/H] trends when compared to the general stellar population of the Galaxy (e.g., Venn et al 2004). In particular, because of a different chemical evolution history, low-[alpha/Fe] ratios are present in stars of lower metallicity than in the Milky Way. It has also become clear that the Galactic halo contains a fraction of stars that has likely been accreted (e.g., Smiljanic et al. 2009). In this work, we compare the chemical abundances of a sample of Galactic metal-poor stars with abundances of stars in dwarf spheroidals. The Galactic stars have been observed within the Gaia-ESO spectroscopic survey. Data for stars in dwarf spheroidals are taken from the literature. Based on the chemical abundances, we identify a subsample of Galactic stars that could have been accreted from external systems. We present an overview of other stellar properties (e.g., kinematics) that might support or reject the accretion hypothesis for these stars.

The research of metallicity effect on the L8-LIR relation in nearby universe

Shao, Xu

SFH plays a fundamental role when people try to understand the evolution of galaxies. FIR observation is considered to be ideal to measure SFR bacause most of the FIR emission arises from dust heated by star formation activities. The low spatial resolution and dust temperature bias of FIR selected galaxies bring the main uncertainty of their SFR estimation. Especially for high redshift galaxies, the peak of their FIR emission has shifted to longer wavelength, such as sub-mm. This will make it difficult to measure their FIR emission and estimate their SFR. To improve these disadvantages, the polycyclic aromatic hydrocarbon (PAH) radiation is introduced to be a tracer of IR luminosity. The PAH selected galaxies have the advantages of high spatial resolution and dust temperature independence. Moreover, PAH emission of galaxies with different redshifts can be observed by different telescopes. Establishing accurate "L8-LIR" relation gives us an opportunity to measure uniform SFR of galaxies with different redshifts and study their evolution.Based on a large PAH selected sample in nearby universe, we studied the metallicity effect on 8um luminosity and "L8-LIR" relation. By cross-matching the Spitzer IRAC 8um photometry catalog with spectral observation of MMT and SDSS, we selected star forming galaxies with PAH emission at 0.02<z&lt;0.3. the="" herschel="" pacs="" and="" spire="" have been="" used="" to="" estimated dust="" temperature="" and far="" infrared="" luminosity.="" we="" find="" that="" lir="" l8="" ratio="" deviates="" from="" main="" sequence="" indicated="" by="" elbaz="" et="" al.="" (2011)="" at="" faint-end="" of="" l8.="" the lir="" keeps="" constant="" 12+log(o="" h)="" &gt;8.6="" becomes="" high="" in="" low-metallicity="" environments.&nbsp;this="" trend="" may="" be="" result="" weak="" pah="" emission="" environment,="" which="" is="" also="" our="" results.="" after="" correcting="" metallicity="" effect="" on&nbsp;lir="" ratio,="" obtained="" accurate&nbsp;&quot;l8-lir&quot;="" relation="" this="" will="" help="" study="" star="" formation="" redshift="" galaxies="" using="" forthcoming="" jwst.<="" z&lt;0.3.&gt;<="" p=""> </z<0.3.></z<0.3.></z<0.3.></z<0.3.></z<0.3.>

Numerical computation of gravitational field of infinitely-thin axisymmetric disc with arbitrary surface mass density profile and its application to preliminary study of rotation curve of M33

Fukushima, Toshio

We developed a numerical method to compute the gravitational field of an infinitely-thin axisymmetric disc with an arbitrary surface mass density profile (Fukushima 2016, MNRAS, 456:3702). We evaluate the gravitational potential by a split quadrature using the double exponential rule and obtain the acceleration vector by numerically differentiating the potential by Ridders' algorithm. The new method is of around 12 digit accuracy and sufficiently fast because requiring only one-dimensional integration. By using the new method, we show the rotation curves of some non-trivial discs: (i) truncated power-law discs, (ii) discs with a non-negligible center hole, (iii) truncated Mestel discs with edge-softening, (iv) double power-law discs, (v) exponentially-damped power-law discs, and (vi) an exponential disc with a sinusoidal modulation of the density profile. Also, we present a couple of model fittings to the observed rotation curve of M33: (i) the standard deconvolution by assuming a spherical distributin of the dark matter and (ii) a direct fit of infinitely-thin disc mass with a double power-law distribution of the surface mass density. Although the number of free parameters is a little larger, the latter model provides a significantly better fit. The Fortran 90 program package of the new method named "xvrot.txt" is freely available from the author's web site:

Strong evidence for a cored dark halo in the Fornax dwarf spheroidal galaxy

Pascale, Raffaele

A knowledge of the present-day dark-matter distribution and internal stellar kinematics of dwarf spheroidal galaxies (dSphs) is important, having implications for both models of galaxy formation and the nature of dark matter. I will present a novel dynamical modelling method of dSphs, based on analytic distribution functions (DFs) depending on the action integrals, which can describe axisymmetric and possibly rotating stellar systems. In particular I will show very recent results (Pascale, Posti, Nipoti & Binney 2018, obtained by applying this method to the Fornax dSph, considering two-component spherical models in which both the stars and the dark matter are described with Dfs. Fornax can safely be modelled as an isolated system, because environment effects due to the Milky Way tidal field have been proven to be negligible. The models are compared with state-of-the-art spectroscopic and photometric observations of Fornax, accounting for the foreground contamination from the Milky Way and exploiting the knowledge of the line-of-sight velocity distribution with a star-by-star analysis. In light of the core/cusp problem we tested both the hypothesis of cuspy and cored dark halos. The model that best fits the structural and kinematic properties of Fornax has a cored dark halo, with corerc ~ 1kpc ~ 1.7 Re, where Re is the effective radius. The stellar velocity distribution is isotropic almost over the full radial range covered by the spectroscopic data and slightly radially anisotropic in the outskirts of the stellar distribution. The dark-matter annihilation J-factor and decay D-factor are strongly constrained. This cored-halo model of Fornax is preferred, with high statistical significance, to both models with a Navarro, Frenk and White dark halo and simple mass-follows-light models.

Internal kinematics of blue-cored early-type dwarf galaxies in the Virgo cluster

Rey, Soo-Chang

Early-type dwarf galaxy (ETDG), the most abundant galaxy type in cluster, have been recently shown to exhibit a wide variety in their properties. Particularly, the presence of blue cores in some ETDGs supports the scenario of late-type galaxy infall and subsequent transformation into red, quiescent ETDGs. While several transformation mechanisms for these ETDGs within cluster environment have been proposed, all these processes are able to explain only some of the observational properties of ETDGs. In this context, internal kinematic properties of blue-cored ETDGs provide the most crucial evidence to discriminate different processes for the formation of these galaxies. We present a kinematic analysis of two blue-cored ETDGs in the Virgo cluster based on long-slit data obtained from Gemini Multi-Object Spectrographs (GMOS) observations. We found that the observed galaxies exhibit kinematically decoupled or disturbed components in the velocity profile. We also found that these galaxies are structurally compatible with low surface brightness component of blue compact dwarf galaxies. We suggest that a part of blue-cored ETDGs in the Virgo cluster were formed through galaxy merger in low density environment such as galaxy group or outskirt of the cluster, and then were quenched by subsequent effects within cluster environment.

The Wolf-Rayet Star Population in Nearby Dwarf Starburst Galaxy NGC 625

Monreal Ibero, Ana

Quantifying the number, type, and distribution of Wolf-Rayet (W-R) stars is a key component in the context of galaxy evolution, since they put constraints on the age of the star formation bursts. Nearby galaxies (distances <5 Mpc) are particularly relevant in this context since they fill the gap between studies in the Local Group, where individual stars can be resolved, and galaxies in the Local Volume and beyond.In this contribution, I will present the characterization of the W-R star population in NGC 625, a low-metallicity dwarf galaxy at ~4 Mpc, by means of optical integral field spectroscopy (IFS) data obtained with the VIMOS-IFU and the HR_Orange and HR_Blue. The number of W-R stars was estimated using a linear combination of three W-R templates: one early-type nitrogen (WN) star, one late-type WN star, and one carbon-type (WC) star (or oxygen-type (WO) star). Fits using several ensembles of templates were tested. Results were confronted with i) high spatial resolution HST photometry; ii) numbers of W-R stars in nearby galaxies; and iii) model predictions. Results of this analysis have been presented in Monreal-Ibero et al. 2017, A&A, 603, A130.

The Lyman Continuum Leakage of the dwarf galaxy Tololo 1247-232 under review

Puschnig, Johannes

The driving mechanism of the reionization of the Universe is yet not well constrained, but low- and intermediate mass galaxies are widely discussed as source of ionizing photons, i.e. Lyman Continuum (LyC). However, proof of emerging LyC emission is an ongoing observational challenge at all redshifts. Using highly resolved photometry and far-UV spectroscopy obtained with the Hubble Space Telescope (HST) as well as interferometric observations performed with the Karl G. Jansky Very Large Array (VLA), we have studied the ionized and neutral gas content in the local dwarf galaxy Tololo 1247-232. My talk is based on Puschnig et al. (2017), describing physical mechanisms that drive the LyC escape in Tololo 1247-232, which is to date one of the very few known/confirmed LyC emitters in the Universe.Using HST's Cosmic Origins Spectrograph (COS), in combination with an improved data reduction routine, we have directly measured the amount of LyC emerging from the galaxy, finding an escape fraction of 1.5+/-0.5 percent only, i.e. the lowest LyC escape fraction reported for the galaxy so far. We further use far-UV absorption line analysis to probe the neutral and ionized gas, e.g. the covering fraction of the neutral medium could be constrained. We show that the LyC photons emerge from density bounded regions and finally escape through a clumpy medium. However, from Lyman Alpha line analysis, we also conclude that an additional diffuse interclump medium must be present that prevents Lyman Alpha to be seen at systemic velocity. The LyC escpae is further supported by our VLA 21cm observations, from which a very low gas fraction of less than 20 percent could be derived.

Intermediate-Mass Black Hole Feedback in Dwarf Galaxies: a View from Cosmological Simulations

Barai, Paramita

Black holes are usually observed to be of stellar-mass or supermassive. By natural extension, there should be a population of Intermediate-Mass Black Holes (IMBHs: with mass between 100 to 106 Msun) in the Universe; which has started to been observed. An exciting claim has been made recently by Silk, J.(2017, ApJ, 839, L13): that there can be IMBHs at the centers of essentially all old Dwarf Galaxies. Early feedback by IMBHs in gas-rich dwarf galaxies at z = 5 - 8, can potentially solve multiple dwarf galaxy problems (e.g. core-cusp, number) within the Lambda-cold-dark-matter cosmology.We are performing Cosmological Hydrodynamical Simulations to test the case for IMBHs in Dwarf Galaxies. Our simulations employ the 3D TreePM SPH code GADGET-3, and include metal cooling, star formation, chemical enrichment, supernova feedback, AGN accretion and feedback (Barai, P. et al. 2016, MNRAS, 461, 1548). We are simulating small (2 Mpc)3 cosmological volumes with periodic boundary conditions, starting from z = 100. Black Holes of mass 1000 Msun are seeded inside halos when they reach a mass of 107 Msun. The black holes grow by accretion of gas from their surroundings and by merger with other black holes, and consequently eject feedback energy. We analyze the simulation output in post-processing to study the growth of the first IMBHs. We quantify the impact of IMBHs on their host Dwarf Galaxies; especially the effects on star formation in terms of negative or positive feedback.Our conclusions, based on numerical simulation results, support the phenomenological ideas made by Silk(2017). IMBHs at the centers of dwarf galaxies can be a strong source of feedback to quench star-formation and generate outflows. At the same time, these IMBHs form the missing link between stellar-mass and supermassive BHs.

A Stellar Proper Motion Map of the Magellanic Clouds

Niederhofer, Florian

The Large and Small Magellanic Cloud (LMC and SMC) are recently acquired satellites of our Galaxy andare currently interacting both with each other and with the Milky Way. The dynamical interplay is most likely responsible for the complex morphology of the two Clouds and the formation of tidal features such as a stellar Bridge connecting the two dwarf galaxies and a gaseous Stream. Thanks to their close proximity (50-60 kpc), they provide a good opportunity to study in detail the kinematics of resolved stellar populations in an interacting pair of galaxies. However, precise and homogeneous stellar proper motion measurements across the LMC and SMC, needed to design dynamical models that describe the formation, orbital history and evolution of the Magellanic system, are still lacking.The ongoing near-infrared VISTA survey of the Magellanic Cloud system (VMC) is specially designed to study in detailmultiple aspects of this interacting pair of galaxies. Thanks to its multi-epoch nature, the VMC data can also be used to derive stellar proper motions. In this contribution, we will present first results from our ongoing project dedicated to measure the proper motions of large samples of stars across the Magellanic Clouds, showing for the first time the large scale velocity field within the Clouds and the small scale motions of individual stellar populations.

Scaling relations and colors of dwarf galaxies

Saifollahi, Teymoor

The Fornax Deep Survey (FDS) (Iodice et al. 2016, Venhola et al. 2017) is a new ultra-deep imaging survey of 30 square degrees in 4 bands, in depth comparable to the Virgo NGVS survey. With as aim the study of galaxy formation and evolution in dense environments, it is studying a wide range of topics, including intracluster light and ultra-diffuse galaxies. My work consists of combining the FDS with near-IR VISTA observations in J and K. Near-infrared emission of galaxies mainly comes from old stellar populations, dominating  the luminous mass of galaxies. In this work, for the first time, we use deep multi-band imaging in u, g, r, i, J and Ks, to map color, age and metallicity in Fornax cluster dwarf galaxies.  Optical/near-infrared colors are good indicators of stellar populations (Roediger et al., 2011 and 2012, Urich et al., 2017) which can be used to break the age-metallicity degeneracy (Galaz et al, 2002). I will discuss scaling relations and radial color gradients.

Physical parameters of RSGs in the Local Group: probing the nature of dIrr galaxies with RSGs.

Britavskiy, Nikolay

In the last years, the red supergiants (RSGs) deserve particular attention in the studies of the galaxies in the Local Group. Their brightness in the near-IR colors together with a new generation of instruments and telescopes will allow to investigate the properties of host environment even with a non-resolved population of other types of stars. In our previous works (Britavskiy et al. 2014, 2015, in prep.) we identified 25 spectroscopically confirmed RSGs in 7 dwarf irregular (dIrr) galaxies in the Local Group. Namely in Sextans A, Sextans B, WLM, Pegasus, Phoenix, IC 10 and IC 1613. The next step is to characterize and connect the physical properties of RSGs with properties of the host dIrr galaxies. We will make a comprehensive overview of the RSG population and will discuss how to get their physical parameters and evolutionary status by using different methods and models in the different host environments. Moreover, on the other way around, we will make a first estimation of the expected RSG population at the given metallicity and star formation rate of each dIrr galaxy, which will make a bridge between the observed properties of RSGs and the nature of dIrr galaxies.

The environmental dependence of the subsolar initial mass function

Gennaro, Mario

Understanding whether the Initial Mass Function (IMF) varies with environment will advance our detailed understanding of star formation and provide an empirical foundation for interpreting the observations of star-forming galaxies throughout cosmic history.In particular, very low-metallicity systems, like Local Group ultra-faint dwarfs, provide clues towards understanding the conditions in which stars formed in the early Universe, before the epoch of re-ionization.I will present recent results from both optical and near-infrared HST observations that probe the stellar populations of 6 nearby ultra-faint Milky Way dwarf satellites down to 0.4 (optical, using ACS) and 0.2 (near-IR, using WFC3) solar masses. Our analysis suggests that the IMF slope of such objects is flatter than that in the Milky Way. We observe a correlation between the IMF slope and the metallcitiy of the galaxies, with the most metal-poor ones having a more bottom-light IMF, i.e., fewer low-mass stars, relative to the Milky Way. Moreover, there is large variance in the IMF shape among the 6 galaxies observed in the optical.Obtaining measurements reaching well below the Milky Way IMF turnover mass of 0.5 Msun is very costly with HST, and feasible only for the closest UFDs.Near-future missions like JWST and WFIRST will help us probe an even smaller mass regime, reaching close to the hydrogen burning limit.

Are Disky Dwarf Galaxies Unstable to Formation of Bars and Spirals?

Kim, Woong-Tae

A fraction of early-type dwarf galaxies in the Virgo cluster have a disk component and even possess disk features such as bar, lens, and spiral arms. Using N-body simulations, we study formation scenarios of these non-axisymmetric features in the disky dwarf galaxies. By adopting VCC 856 as our progenitor, a bulgeless dwarf disk galaxy with embedded faint spiral arms, we construct 15 initial conditions with slight dynamical variations based on observational error ranges and evolve them in isolation. Our standard model slowly forms a bar at ~3 Gyr and then undergoes buckling instability that temporarily weakens the bar, although the bar strength continues to grow afterward. Nine of our isolated models are also unstable to bar formation. This suggests that the disky dwarf galaxies are intrinsically unstable to form bars, accounting for a population of barred dwarf galaxies in the outskirts of the Virgo cluster. We also find that both the concentration of dark matter halo and the degree of random motions within stellar disk affect the vigor of buckling instability. To examine tidal effects from neighboring galaxies and a cluster, we additionally construct galaxy-galaxy and galaxy-cluster models by differing pericenter distances. We find that weak tidal interactions drive faint spirals, while strong encounters result in bars. Furthermore, our result of galaxy-cluster models shows that the tidal force in the cluster outskirts is insignificant in bar formation.

VMC Proper motions of the outer LMC and the Magellanic Bridge

Schmidt, Thomas

Dwarf galaxies enable us to study early phases of galaxy evolution and are key to many open questions about the hierarchical structure of the Universe. The Large and Small Magellanic Cloud (LMC and SMC) are the most luminous dwarf galaxy satellites of the Milky Way. They are most likely gravitationally bound to each other and their last interaction occurred about 200 Myr ago. In addition, they are in an early phase of minor merging with the Milky Way and will impact the Galactic structure in the future because of their relatively large mass. However, there are still major uncertainties regarding their origin and their interactions with one-another and with the Milky Way.To gain greater insight into the Magellanic system, we used the VMC (VISTA near-infrared survey of the Magellanic Clouds) to calculate proper motions. These are used to study the internal kinematics of the galaxies and their interaction, which is possible due to the multi-epoch nature of the VMC survey. In this contribution, I am going to present first results on the study of the Large Magellanic Clouds and the Magellanic Bridge.

Ram pressure stripping effect on dwarf galaxies in the Virgo cluster

Lee, Woong

We investigate star formation quenching of galaxy population in the Virgo cluster under ram pressure stripping effect using VLA Imaging of Virgo spirals in Atomic gas (VIVA) survey data. We adopted four subgroups of 40 VIVA galaxies at various stages of ram pressure stripping (pre, early, active, and past) classified by Yoon et al. based on the basic HI properties. Assuming that low-mass galaxies around massive VIVA galaxies are likely to be influenced by the similar level of ram pressure effect, we selected neighbor galaxies possibly associated with each VIVA galaxy using kinematic data from the Extended Virgo Cluster Catalog (EVCC). Additionally, we also classified galaxies in VIVA and Ursa Major group without any hint of gas stripping. We investigate optical and ultraviolet (UV) photometric properties of galaxies in four subgroups spanning a wide range of brightness (-21 <mr <="" -12)="" using="" sdss="" optical="" and="" galex="" uv="" data.="" in="" the="" near-uv="" (nuv)="" -="" r-band="" color-magnitude="" relation,="" nuv-r="" colors="" of="" galaxies="" subgroups="" become="" redder="" with="" ram="" pressure="" stripping="" stages,="" which="" is="" good="" agreement="" orbital="" history="" described="" by="" yoon="" et="" al.="" a="" phase-space="" diagram.="" we="" find="" that="" faint,="" dwarf="" active="" past="" are="" more="" rapidly="" quenched,="" while="" massive="" counterparts="" still="" star="" formation="" activity.="" observationally="" confirm="" effect="" critical="" process="" for="" star-forming="" systems="" into="" a red="" galaxy="" cluster="" environment,="" especially="" low-mass="" on="" very="" short="" timescale.="" other="" hand,="" lower="" dense="" environments="" outskirt="" group,="" gravitational="" influence="" nearby="" could="" not="" be="" enough="" passive="" evolution="" neighbor="" from="" blue="" cloud.<="" p="">

Star formation histories of the LEGUS dwarf galaxies

Cignoni, Michele

I will present the detailed recent star formation history (SFH) of dwarf galaxies between 3 and 12 Mpc from the Legacy ExtraGalactic UV Survey (LEGUS). This sample includes a variety of morphologies and densities, such as the diffuse and low density Holmberg II, the Magellanic irregular NGC4449 and the Blue Compact NGC1705. The SFHs are derived by comparing deep UV color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs. In order to assess the uncertainties related to stellar evolution modelling, two independent sets of stellar isochrones are used: PARSEC-COLIBRI and MIST. The SFHs derived with the two different sets of stellar models are consistent with each other, except for some quantitative details, attributable to their input assumptions. I will discuss how these SFHs compare with previous optical CMD studies and integrated SFR measurements (Hα and UV). Critical insights into the evolution of massive main-sequence and helium-burning stars will be also provided.

A near-infrared VISTA of the Small Magellanic Cloud

Cioni, Maria-Rosa

VISTA observed the Small Magellanic Cloud, as part of the VISTA survey of the Magellanic Clouds system (VMC), for six years (2010-2016). The acquired multi-epoch YJKs images have allowed us to probe the stellar populations to an exceptional level of detail across an unprecedented wide area in the near-infrared. In this contribution, I will review the VMC results obtained on the SMC focusing in particular on the most recent investigations of the parameters and distribution of its stellar populations. I am also going to present the first complete public VMC data release of the SMC.

Preparing for the WEAVE Galaxy Clusters survey: XSL-based stellar population models

Verro, Kristiina

With the next generation wide-field spectroscopic facility WEAVE for the William Herschel Telescope, dwarf galaxies in different environments up to a redshift of 0.04 will be accessible. WEAVE’s Galaxy Clusters survey will provide single-fibre and IFU spectroscopic information for thousands of dwarfs, with resolving power R = 5000, and 366-959 nm wavelength coverage. We are developing a new interpolator and stellar population models based on X-Shooter spectral library (XSL) that will exceed the resolving power and wavelength coverage of WEAVE. The XSL covers the entire HR diagram, including M dwarfs and M giants that help us understand the old stellar populations of early-type dwarf galaxies. The new stellar populations models will allow us to study early-type dwarfs in clusters, answering questions about the influence of the environment on these systems.

Resolving the ancient star formation of dwarf galaxies in the Local Group and beyond.

Savino, Alessandro

I will present a new approach that, for the first time, combines classical colour-magnitude diagram analysis with horizontal branch modelling, allowing to measure the star formation history of resolved galaxies with greater precision and detail than previously done. The combined modelling of many features on the colour-magnitude diagram helps to soften the age-metallicity degeneracy and permits to recover the ancient star formation of nearby galaxies with a precision of ~500 Myr. I will present the results of this modelling on a sample of Local Group dwarf spheroidal galaxies. The horizontal branch in all these galaxies show signs of a more complex ancient star formation history than has previously been realized. I will explain how the horizontal branch can be used to reveal detailed ancient star formation properties and look for commonalities in the early history of a sample of galaxies that are probes of the state of the Local Group in the early Universe. With the advent of next generation facilities, this new method has also the potential to extend or knowledge of ancient stellar populations to neighbouring galaxy groups, within several Mpc, providing a meaningful comparison with simulations over a cosmological representative volume.

H2 and HI clouds in dwarf galaxies

Hojaev, Alisher S.

Based on radio astronomy data available in special resources and using the data mining technology (aka, knowledge discovery in databases, KDD) the general catalog of extragalactic molecular and atomic hydrogen clouds and nebula was created and analyzed. Although the main part of such objects is located in spiral galaxies at different distances from the Milky Way Galaxy a few samples of dwarf galaxies also have such structural elements as well, according to the observational data. In accordance with the range of their masses and sizes as well as other physical parameters the observed clouds are of giant and hyper-giant molecular cloud class objects. The statistical and physical correlation analyses were made on clouds features and basic physical parameters. The results were compared with other types of galaxies where the molecular and atomic hydrogen clouds and nebula were ever observed. The gaseous clouds of both dwarf irregular galaxies and giant spirals are apparently located near the boundary of gravitational instability that promotes active star formation. The theoretical modeling of dynamical evolution of these galaxies as well as massive star formation in low [Fe/H] environment are also considered and discussed.

Searching for Winds in Starbursting Low-Mass Galaxies from STARBIRDS

McQuinn, Kristen

Mass-loss via stellar-feedback driven outflows is predicted to play a critical role in the baryon cycle of low-mass galaxies. However, observational constraints on warm winds are limited as outflows are transient, intrinsically low-surface brightness events and, thus, difficult to detect. Here, we search for outflows in a sample of eleven nearby starburst dwarf galaxies which are strong candidates for outflows based on their recent star formation histories derived from HST optical imaging of resolved stellar populations. We trace the warm gas phase, which is expected to carry the greatest amount of gas mass, using very deep Hα observations reaching 31 mag arcsec-2 from the KPNO Mayall 4m and the University of Arizona 2.3m Bok telescopes. Despite the deep imaging on galaxies biased towards hosting winds, the observational signature of gaseous outflows is still subtle. Only a fraction of the sample show evidence of winds and these are preferentially found in galaxies with centrally concentrated star formation. We suggest that the concentration of star formation is a predictor for whether a low-mass galaxy will develop a wind. The spatial extent of all detected ionized gas is limited and would still be considered part of the ISM by simulations. We calculate the mass-loading factors of winds based on the Hα emission and compare these to numbers from the latest predictions from hydrodynamical simulations. These observations indicate that (i) the physical extent of warm phase outflows is modest, (ii) most of the mass will be recycled to the galaxy, (iii) the frequency of winds - even in a biased sample - is lower than expected. The sample is part of the panchromatic STARBurst IRegular Dwarf Survey (STARBIRDS) designed to characterize the starburst phenomenon and its impact on the evolution of low-mass galaxies.

A Multi-Frequency Radio Continuum Study of the Magellanic Clouds

For, Bi-Qing

We present the first SKA precusor Murchison Widefield Array (MWA) radio continuum maps of the Magellanic Clouds. In this talk, we discuss the overall radio continuum morphology between 76 and 227 MHz and compare them_x000D_ with neutral hydrogen maps, 1.4 GHz continuum maps and optical images. We also measure the integrated flux densities and derive the global spectral indices. Variation of diffuse emission is noticeable across the Large Magellanic Cloud (LMC) but absent across the bar of the Small Magellanic Cloud (SMC). The radio spectral index maps reveal distinctive flat and steep spectral indices for the HII regions and supernova remnants, respectively. We find strong correlation between HII regions and Halpha emission. Using a new 150 MHz--Halpha relation as a star-formation-rate indicator, we estimate global star formation rates for the LMC and SMC, respectively. Information regarding data release will be provided.

The First Homogeneous Catalogue of Ultra-Compact Dwarf Galaxies in the Virgo Cluster and Related Studies

Liu, Chengze

For many decades, it was widely believed that galaxies and star clusters were completely distinct populations. However, in the late 1990s, a new type of compact stellar system, Ultra-Compact Dwarf galaxies (UCDs), was discovered to have some properties that bridged the gap between compact, dwarf galaxies and globular clusters. More than 15 years after their discovery, the origin of UCDs remains surprisingly obscure. In this talk, based on NGVS data, we will report the first homogeneous catalogue of UCDs in Virgo cluster and provide evidence that tidal stripping of nucleated galaxies is probably the dominant process in the formation of UCDs._x000D_ We show how UCDs can be selected with high completeness using a combination of magnitude, half-light radii and location in the color-color diagrams. _x000D_ Most of UCDs are around the three largest galaxies in the Virgo cluster: M87, M49 and M60. Although these three galaxies have nearly identical luminosities and stellar masses, we find large differences in the sizes of their UCD populations, with M87 containing ~ 3.5 and 7 times as many UCDs as M49 and M60, respectively. _x000D_ We show for the first time that the UCDs, like the globular clusters in most high-mass galaxies, show a bimodal distribution in color with ~80% of the UCDs belonging to the blue sub-population. _x000D_ We report the discovery of the most massive UCDs, M59-UCD3, in Virgo cluster. With an effective surface mass density of 9.4×1010 Msun/kpc2, it is the densest galaxy in the local universe discovered to date. _x000D_ We present evidence that UCDs in Virgo core may follow a morphological sequence ordered by the prominence of their outer, low surface brightness envelope, ultimately merging with the sequence of nucleated low-mass galaxies, and that envelope prominence correlates with distance from the center of Virgo cluster.

Dwarf Galaxies and Cluster Environments

Hashimoto, Yasuhiro

We report an investigation of the properties of dwarf galaxies (Mr < -15) inside 26 clusters at z=0.15-0.25, using optical images taken with 34' x 27' field-of-view Subaru Suprime-Cam and the X-ray data from the Chandra archive._x000D_ Our goal is to help understand the relationship between the dwarf and giant galaxies, and between the dwarfs and their host clusters to eventually address a question of the formation and co-evolution of galaxies and their environments._x000D_ Our results include:_x000D_ 1. Investigation of the dwarf galaxy density distribution is sensitive to the background galaxies and the choice of colour selection of galaxies._x000D_ 2. Under-estimating of the background galaxy counts tends to mimic a `flat' distribution of dwarf galaxies over cluster-centric distance. _x000D_ 3. Approximately 40 - 60% of faint galaxies always remain undetected by the detection algorithm near the center of clusters, even after carefully treating the halo or extra diffuse light created by bright galaxies. The number of 'undetected' faint galaxies varies significantly from cluster to cluster, and even from pointing to pointing. Meanwhile, the distribution of blue (more than 0.3 bluer than cluster red sequence V-I colour) dwarf galaxies extends more to the outside_x000D_ 4. Dwarf galaxies extend up to 2 Mpc from the center in most clusters. Meanwhile, the distribution of blue (more than 0.3 bluer than cluster red sequence V-I colour) dwarf galaxies extends more to the outside compared to red dwarf galaxies._x000D_ 5. For a given colour, the spatial distributions of dwarf galaxies and giant galaxies become similar, once the accurate background correction is applied. Namely, the major contribution to the difference in the radial distribution comes from the colour, rather than the size, of galaxies._x000D_ 6. Relative to the NFW profile, all of the galaxy populations are showing a deficit near the cluster core (r < 0.3 Mpc). The deviation is the most significant for blue dwarf galaxies.

DDO68-V1: an extremely metal-poor LBV in a void galaxy

Perepelitsyna, Julia

The lowest metallicity massive stars in the Local Universe with Z ~ (Zo/50-Zo/30) are the crucial objects to test the validity of assumptions in modern models of low-metallicity massive star evolution. These models, in turn, have major implications for our understanding of galaxy and massive star formation in the early epochs. The great progress in the area is expected with the next generation facilities like JWST and extremely large telescopes. One of the most interesting targets of this kind is the massive star DDO68-V1 in a nearby void galaxy DDO68. Discovered by us in 2008 in the HII region Knot No.3 with Z = Zo/35 [12+log(O/H)=7.14], DDO68-V1 was identified as a luminous blue variable star (LBV). We present here the LBV lightcurve in V and B bands, combining own new data and the archive and/or literature data on the light of Knot No.3 over the last 30 years. We find, in particular, that during the years 2008-2011 the LBV have experienced a very rare event of the giant eruption with the V-bavd amplitude of ~4 mag (V~24-20 mag).

"Observations" of Simulated Dwarf Galaxies

Rathi, Shivangee

Dwarf galaxies are ideal systems to test the LambdaCDM cosmological theory for galaxy formation and evolution. Despite LambdaCDM's success in correctly reproducing large scale phenomena, it faces serious challenges on small scales, in the dwarf galaxy regime. One such persistent problem in the dwarf regime is the too-big-to-fail (TBTF) problem, which is an apparent mismatch between the expected number density of dwarf galaxies and their observed kinematics. We present our recent efforts to overcome these issues by bringing the analysis of dwarf galaxy simulations as close as possible to the observations. To this end, we construct synthetic radio datacubes for the simulated MoRIA suite of dwarf galaxies (Verbeke et al. 2015) and use observational tools such as GIPSY and 3DBarolo to analyze and interpret the HI kinematics of these simulated dwarfs. We show that this has consequences for the TBTF problem.We also reconstruct the star-formation histories (SFHs) of these simulated dwarfs based on their synthetic stellar Color-Magnitude diagrams using the techniques developed by the LCID team (Aparicio, A & Hidalgo, S. L. 2009). We compare this with the SFHs drawn directly from the simulations and discuss the effects of using different stellar evolution libraries. We emphasize the applicability and importance of using observational techniques to properly analyse simulated dwarf galaxies in order to robustly and reliably test LambdaCDM.

The ISM properties of low-mass galaxies with extremely strong emission lines at z=0.3-0.8 discovered with Subaru/HSC

Yabe, Kiyoto

Revealing the nature of low-mass galaxies with strong emission lines is of importance to understand the early stage of galaxy formation and evolution. The detailed studies at high redshift, however, are not easy because of various observational limitations. Thus, it is important to examine similar galaxies at lower redshift in details. Thanks to its deep and wide imaging data, we are conducting a survey to search for strong emission line galaxies by using Subaru Hyper Suprime-Cam (HSC). We select candidates of strong emission line galaxies at up to z~0.8 with excesses of broad-band filters. The selected galaxies correspond to high redshift version of Green Pea galaxies in the SDSS, which are thought to be similar to galaxies in the early Universe. Our spectroscopic follow-up for the candidates is currently ongoing. In a previous observation, we confirmed the spectroscopic redshift of 19 galaxies at z=0.35-0.83 using Gemini/GMOS-S. From 4 galaxies, we detected very strong [OIII]5007 emission with the rest-frame equivalent width of > 1000A and other multiple emission lines including weak [OIII]4363 with high significance. The stellar mass  ranges from ~10^7 to ~10^9 Msun and the SFR ranges from ~0.1 to ~1000 Msun / yr. According to the stellar mass and [OIII]5007/Hb ratio, the contribution from active galactic nuclei (AGNs) seems to be low. The [OIII]5007/[OII]3727 emission line ratio ranges from ~3 to ~10, which is comparable to that of the SDSS Green Pea galaxies and Lya emitters (LAEs) at z=2-4, indicating extreme ionization states. The resulting oxygen abundance based on the “direct” method using [OIII]4363 is 12+log(O/H)<8.0. One of the sample shows very low oxygen abundance of 12+log(O/H)~7.3, which is comparable to extremely metal poor galaxies in the local Universe. In this presentation, we give an overview of our project and discuss the possible origin of these galaxies with low metallicity and high ionization state.

Star forming activity and chemical evolution of the IC10 dwarf galaxy

Gholami, Mahtab

Star forming activity and chemical evolution of the IC10 dwarf galaxyMahtab Gholami1, Atefeh Javadi2, Jacco Th. van Loon3, Habib Khosroshahi2, Mohammad Taghi Mirtorabi1 and Elham Saremi2,4.1 Physics Department, Alzahra University, Vanak, 1993891176 Tehran, Iran2 School of Astronomy, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5531 Tehran, Iran3 Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG, UK4 Physics Department, University of Birjand, Birjand 97175-615, Iran Amongst the dwarf galaxies in the Local Group, the isolated irregular one, IC10 is one of the most interesting galaxies, with strong star forming activity and the highest density of Wolf-Rayet stars. Undergoing a starburst phase, having numerous HII regions and being bright in all wavebands, makes it an exquisite galaxy to study the internal and external processes that continue to affect dwarf galaxies 14 Gyr since the Big Bang. In this study, we present a new deep and precise optical monitoring survey of IC10 using the Isaac Newton Telescope (INT) with the wide field camera (WFCAM). We performed observations at nine epochs spaced between three to four months apart between 2015 and 2018. We identified Long Period Variable stars (LPVs) and Asymptotic Giant Branch stars (AGBs) to determine the star formation history and chemical evolution of IC10.

Nearby void dwarf galaxies: recent results, the ongoing project and prospects

Pustilnik, Simon

Properties of dwarf galaxies formed and evolved in the lowest densityenvironment still remain largely unexplored and poorly understood. Especiallythis concerns the low-mass end, namely at M_B > -14, M_bar <~10^9 Mo. Weoverview the results of the only systematic study of the faintest void dwarfsbased on the sample of hundred galaxies in the nearby Lynx-Cancer void. Furtherwe describe the ongoing project aiming to form and study a nearby void galaxysample (R < 25 Mpc) over the whole celestial sphere. About 1500 objects of6830 known galaxies with distance less than 25 Mpc fall within 25 voidsdelineated by ~460 luminous galaxies/groups. The major sizes of voids rangefrom ~13 to ~28 Mpc. About 1150 of 1500 void galaxies reside deeply in voids,having distances to the nearest luminous neighbour of 2-11 Mpc. About 330 ofthem have M_B > -14, with the faintest objects reaching M_B~-10. About 200nearest void galaxies reside in the Local Volume (D < 11 Mpc). We summarizethe main statistical properties of the nearby void galaxy sample and someunexpected findings, and outline the prospects of study of both, the voiddwarf properties and the fine structure of voids.

Galactic ambient of host galaxies of GRBs

Vásquez, Nicolás

The study of GRBs host galaxies and its vicinity could provide constrains on the progenitor and an opportunity to use these violent explosions to characterize the nature of the high redshift universe. Studies of host galaxies of Gamma Ray Burst reveal a population of starforming galaxies with great diversity, spanning a wide range of masses, star formation rate, and redshifts. In order to study the galactic ambient of GRBs we used the S. Savaglio catalog from 2015 where 245 GRBs are listed with RA-Dec position and z. We choose 50 GRBs Hosts galaxies from Savaglio catalog and SDSS DR12, and galaxies in a local vicinity of 10 h -1 Mpc radius to determine some photometric and population characteristics. We calculate the volumetric density population of galaxies around the GRB Hosts, within a volume of an sphere whit radius of 10 h -1 Mpc and find a low density compared with a typical group of galaxies. In order to know the galaxies stellar formation state, in regions where GRBs are formed, we made an analysis of color index using SDSS data of µ [? 3543], r[? 6231] and calculate the indexes µ-r. We find a value µ-r=2.63, it means that the galactic ambient of GRBs Host regions are statistically redder than void and wall regions on a indirect way (Voids:µ-r=2.043; Walls:µ-r=2.162). Futhermore, we used a inverse concentration index analysis, ICI=R 50 /R 90 and find that galaxies in GRBs Hosts vicinity are also of slightly early type than void and wall galaxies.

The origin of Wolf-Rayet stars at the low metallicity environment of the Magellanic Clouds

Shenar, Tomer

Through their radiation, stellar winds, and supernova explosions, massive stars shape the evolution of their host galaxies. Wolf-Rayet (WR) are evolved, hydrogen depleted massive stars that exhibit strong mass-loss and dominate the stellar feedback on their environments. It is generally not known whether the majority of WR stars in the Magellanic Clouds originate via stripping in binary systems or via intrinsic stripping due to mass-loss. We performed a complete spectral analysis of all known WR binaries in the Small and Large Magellanic Clouds (SMC, LMC), as well as additional orbital analyses, and constrained the evolutionary histories of these important stars. In my talk, I will summarize our study's findings regarding the origin of WR stars in the Magellanic Clouds and their feedback on their environments. I will further describe the our study's implications on gravitational wave progenitors and on the initial mass function as at sub solar metallicities.

Probing Dwarf Galaxies in Low Density Environments

Marleau, Francine

Recent discoveries on dwarf galaxies, such as their planar rotationaround the Milky Way and Andromeda galaxies, have challenged ourunderstanding of galaxy formation and evolution. While these dwarfgalaxies and others in the Local Group and in a few nearby clustershave been studied in considerable detail, relatively few observingprograms have focused on the study of this population of galaxies inlow density environments. Using the optical data obtained in thecontext of MATLAS, a deep imaging large program at CFHT, we havesystematically assembled the largest sample of dwarf galaxies in lowdensity environments. These dwarfs have magnitudes, surfacebrightnesses and sizes comparable to their Local Group and clustercounterparts. I will present results on their visual classification,2D surface brightness profile fitting, local environment andclustering properties, and discuss how these new findings impact ourcurrent understanding of how these galaxies form and evolve.

Star formation and environment: a step in understanding the formation and evolution of local dwarf galaxies

Sacchi, Elena

Over the past several years, it has become increasingly clear that the large-scale star formation is determined by a hierarchy of processes spanning a vast range of physical scales, and that different physical processes may lead to star formation in different interstellar and galactic environments. For nearby galaxies, we have the advantage of resolving the single stars, to study their stellar populations and star formation histories (SFHs) with the synthetic color-magnitude diagram technique and refine stellar evolution models by comparing them with the data. Within this framework, I will discuss the results obtained for the dwarf galaxies part of the HST Legacy ExtraGalactic UV Survey (LEGUS), whose aim is to investigate and connect the different scales of star formation, from young stellar clusters to local Universe galaxies. Our targets were studied both in the UV and optical bands, in order to recover their SFH from very recent to older epochs and to understand whether and how the star formation process may depend on the morphological, dynamical and environmental properties of the galaxies. In particular, we analyzed DDO 68, a very metal-poor dwarf irregular, and NGC 4449, a Magellanic irregular, finding clear correlations of SF enhancement with merging and interactions.

Modeling of the full galaxy stellar mass function evolution

Salvador-Solé, Eduard

We present the results of AMIGA, a very complete self-consistent galaxy formation model that provides excellent fits to all the observed 13 independent cosmic histories, including the star formation and stellar mass density histories, of the Universe from z=15 to z=0. We show the predicted galaxy stellar MFs, derived down to the lowest galaxy stellar mass formed at every redshift. At the high-mass end those theoretical MFs fit the empirical ones derived from observation. At the low-mass end, they unveil the evolution of the dwarf galaxy population that is consistent with all the observed global cosmic properties.

Ultra Diffuse Galaxies: a formation scenario

di cintio, arianna

A large number of Ultra-Diffuse Galaxies (UDGs) has been detected over the past few years, both in clusters and in isolation. UDGs have stellar masses typical of dwarf galaxies but effective radii of Milky Way-sized objects, and their origin remains  puzzling.Using hydrodynamical zoom-in simulations from the  NIHAO project we show that UDGs form naturally in dwarf-mass haloes, as a result of episodic gas outflows associated with star formation. The simulated UDGs live in isolated haloes of masses 1010-11Msun, have stellar masses of 107-8.5Msun, effective radii larger than 1 kpc and dark matter cores. Remarkably, they have  a non-negligible HI gas mass of 107-9Msun, which correlates with the extent of the galaxy.Gas availability is crucial to the internal processes that form UDGs: feedback driven gas outflows, and subsequent dark matter and stellar expansion, are the key to reproduce faint, yet unusually extended, galaxies.This scenario implies that UDGs represent a dwarf population of low surface brightness galaxies and that they should exist in the field.Several predictions and comparisons with stat-of-the-art observational data will be presented. Amongst other, we will show that the largest isolated UDGs sistematically contain more HI gas than less extended dwarfs of similar M*, corroborating our proposed formation scenario.

Full-spectral fitting techniques to characterise the stellar content in ultra diffuse galaxies

Ruiz-Lara, Tomás

Understanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via spectroscopic analysis is a challenging task that is now becoming feasible. The advent of 10m-class telescopes and high sensitivity instruments is enabling the gathering of high quality spectra even for the faintest systems. In addition, advances in the modelling of stellar populations, stellar libraries, and full-spectral fitting codes are allowing the recovery of the stellar content shaping those spectra with unprecedented reliability. In this talk we report on the extensive tests we have carried out using  the inversion code STECKMAP. The similarities between the Star Formation Histories (SFH) recovered from STECKMAP (applied to high-quality spectra) and deep Colour-Magnitude diagrams fitting (resolved stars) in two Local Group dwarf galaxies (LMC and LeoA) are remarkable, showing the impressive performance of STECKMAP. We exploit the capabilities of STECKMAP and perform one of the most complete and reliable characterisations of the stellar component of UDGs to date using deep spectroscopic data. We measure recession and rotation velocities, SFHs and mean population parameters for a sample of UDGs in the Coma cluster. We prove the true UDG nature of three of the systems, not finding significant differences between the stellar populations of dwarf galaxies and UDGs. The SFHs of all the analysed galaxies are dominated by an old, metal-poor and alpha-enhanced population followed by a decline in the star formation which halts ~2Gyr ago (consistent with a bursty-declining SFH). As a consequence, we claim that UDG properties are independent of their SFHs. We also provide evidences favouring a dwarf-like rotation for UDGs. Accordingly, we suggest that UDGs are extended dwarfs whose properties are the outcome of internal processes (high-spin halo and/or bursty SFHs) as well as environmental effects for those located in groups or clusters.

The II Zw 40 Super Nebula

Leitherer, Claus

We discuss HST COS G140L spectroscopy of the enigmatic nearby blue compact dwarf galaxy II Zw 40. The galaxy hosts a nuclear super star cluster with a luminosity 10 times that of 30 Doradus, the most powerful giant HII region in the Local Group. The super star cluster has been suggested to be the ionizing source of a ”supernebula” detected via its free-free radiation in the radio. The physical conditions, however, are much more complex, as demonstrated by the detection of the nebular He II and the mid-infrared line of [O IV] 25.9. These lines are unlikely to be related to hot stars and require a different powering source. II Zw 40 shares many similarities with the related blue compact dwarfs NGC 5253 and Henize 2-10. However, II Zw 40’s UV spectrum is unique in terms of the exceptional strength of He II 1640, O III 1663 and CIII 1909. We determined reddening, age, and the stellar initial mass function and perform a comparison with the local benchmark 30 Doradus. Photoionization modeling is used to determine the origin of the nebular lines as due to stellar ionization, shocks, or powering by a black hole. Series deficiencies in the stellar evolution models are revealed by the presence of excessively strong stellar He II.

Neutral Hydrogen in Nearby Dwarf Galaxies

Koribalski, Baerbel

I will present the gas content, kinematics and star formation observed in nearby dwarf galaxies (D < 10 Mpc), based on the Local Volume HI Survey (LVHIS, Koribalski et al. 2018) and similar interferometric surveys. The LVHIS sample consists of nearly 100 galaxies, including new discoveries, spanning a large diversity in size, shape, mass and degree of peculiarity. The hydrogen properties of dwarf galaxies in two nearby groups, Sculptor and CenA / M83, are presented and compared with many rather isolated dwarf galaxies. Around 10% of LVHIS galaxies are transitional or mixed-type galaxies (dIrr/dSph), the formation of which is explored. I will also give a brief update on WALLABY Early Science, which has focussed on HI in galaxy groups and clusters, based on observations with wide-field (30 sq degr) ASKAP Phase Array Feeds.

Enrichment of heavy elements in chemo-dynamical simulations of dwarf galaxies

Hirai, Yutaka

Recent astronomical observations have shown that there are large star-to-star scatters in the abundances of r-process elements and increasing trend of Zn in extremely metal-poor stars. However, it is not yet clear how the early chemo-dynamical evolution of dwarf galaxies affects the abundances of heavy elements. Here we report that high-resolution N-body/smoothed particle hydrodynamics simulations of dwarf galaxies. We find that galaxies with star formation rates less than 0.001 solar masses per year reproduce the observed abundances of r-process elements assuming that neutron star mergers are the major astrophysical sites of r-process. On the other hand, r-process elements appear at a higher metallicity in galaxies with star formation rates greater than 0.01 solar masses per year. We also find that the ejecta from electron-capture supernovae contribute to stars with [Zn/Fe] > 0.5. The scatters of heavy elements mainly come from the inhomogeneity of the metals in the interstellar medium. We estimate that timescale of metal mixing is less than 40 Myr using heavy element abundances in metal-poor stars. This timescale is lower than that of typical dynamical times of dwarf galaxies. We also find that the r-process enhanced stars seen in the Milky Way halo are formed in halos with a size of ultra-faint dwarf galaxies by using our high-resolution cosmological zoom-in simulations. Our results demonstrate that the future observations of the abundances of heavy elements in extremely metal-poor stars using forthcoming facilities will be able to constrain the early chemo-dynamical evolution of the Local Group dwarf galaxies.

Solo Dwarf Galaxy Survey: Exploring Isolated Dwarfs in the Local Group

Higgs, Clare

The Solo (Solitary Local) Dwarf Galaxy Survey is a volume limited sample of all nearby (< 3 Mpc) and isolated ( > 300 kpc from the Milky Way or M31) dwarfs, with wide-field g and i imaging. This survey uses resolved stellar populations to parameterize these low mass systems. Comparison to the well studied satellite dwarfs characterizes the evolutionary impact of a large galaxy in close proximity. The deep, wide field nature of this survey also lends itself to searching for substructure around these dwarfs, both globular clusters and possible faint satellites. I present a subset of the closest Solo dwarfs, all within the virial radius (approximately 1 Mpc) of the Milky Way. This sample has been characterized using consistent methods, despite the diversity in mass and size between these dwarfs. The analysis focuses on extended stellar structure and morphology, using resolved stellar populations. We then examine trends with star formation history, separation from a large host galaxy, and HI structure . This first subset emphasizes the unique challenges and advantages of this survey. In addition, I present a first look at a complete census of globular cluster candidates within these dwarfs. The Solo Survey provides detailed look at the extended structure of nearby dwarfs and aids in characterizing the evolution of galaxies in the faint limit.

The Nature of Ultra-diffuse Galaxies in Massive Galaxy Clusters

Lee, Jeong Hwan

Ultra-diffuse galaxies (UDGs) are an intriguing galaxy population, because they are as large as the Milky Way but have surface brightness fainter than typical dwarf galaxies.The origin of the UDGs has been controversial: whether they are massive giant galaxies which failed forming stars or they are extended dwarf galaxies.The Hubble Frontier Fields (HFF) program is useful to study the UDGs in massive galaxy clusters.In this study, we present our search for UDGs in three massive clusters, Abell 2744 (z=0.308), Abell S1063 (z=0.348), and Abell 370 (z=0.374), using deep images of the HFF.We find a large amount of UDGs in each cluster.The color-magnitude relations show that the colors of most UDGs are consistent with the faint end of the red sequence of the cluster members.This suggests that UDGs are mainly composed of old stars.However, a few blue UDGs indicate the presence of young stars.This implies that not all cluster UDGs are quenched.The stacked radial number density profiles of UDGs show a flattening feature in the central region, in contrast with those of bright galaxies. This implies that tidal disruptions contribute to the lower number density of UDGs in the central region of the clusters.We indirectly estimate the virial masses (M_200) of the UDGs using the fundamental manifold.The virial masses of most UDGs range from 10^10 M_Sun to 10^11 M_Sun, suggesting that they are dwarf-origin UDGs.However, several UDGs have virial masses larger than 10^11 M_Sun, indicating that they are failed giant galaxies.In conclusion, UDGs in massive galaxy clusters are formed via both dwarf and giant origins.

Towards resolving the globular cluster problem in the Fornax dSph in LambdaCDM

Leung, Gigi

The presence of globular clusters (GCs) at large galactocentric distances in the Fornax dSph challenges our understanding of the dark matter distribution in dwarf galaxies.  Suggested solutions to this problem either invoke a very large initial galactocentric distance for these GCs, or only aim to produce an orbital decay timescale larger than the Hubble time but not the final locations of the GCs.  On the other hand, numerical simulations have shown a dynamical buoyancy effect in which GCs are pushed outwards in cored dark matter halos.  Although this effect partially alleviates the problem, these numerical simulations provide neither an understanding of the physical origin of the buoyancy effect nor a quantitative constraint on the core size.  Here, we present a semi-analytical treatment of dynamical friction that is able to reproduce the buoyancy effect found in N-body simulations.  The essential ingredient to include is the effect of background (dark matter) particles that move faster than the infalling GCs, a component that has been neglected in previous works but is important for cored profiles.  We constrain the initial locations of the GCs in the Fornax dSph based on pressure equilibrium between the GCs and a progenitor gas disk for this galaxy.  To reproduce the observed locations of all the GCs in this galaxy, a dark matter core with a size of at least 4 times that predicted by ?CDM simulations of dwarf galaxies with baryonic feedback is required.  A potential resolution to this disagreement may lie in a proper consideration of the past merger history of this galaxy.

An analysis of M31 and its satellites' populations through RR Lyrae.

Tanakul, Nahathai

RR Lyrae variable stars are powerful tools to study their host stellar populations. Information such as distance, metallicity, reddening, and age can be obtained from their pulsation properties.  Dwarf spheroidal (dSph) galaxies are the most common type galaxies in the Local Group. They are found around massive hosts such as the Milky Way (MW) and M31 and are suggested to be the present-day counterparts to systems from which spheroids and stellar halos of larger galaxies were assembled. By comparing RR Lyraes in these dSphs and their host galaxies, we might understand more about the formation of these galaxies. In this study, we aim to: 1) Investigate the Oosterhoff type of RR Lyrae stars in M31 and its satellites including eight dSphs and compare them with the MW to better understand the formation of these galaxies. 2) Investigate the early formation history of these galaxies through knowledge of their RR Lyrae stars. In order to achieve these goals, we have analyzed 6 fields in M31 using archival imaging from the Hubble Space Telescope. Published data for M31, M33, and several M31 dSphs are also included. The results are then compared with those in the MW to better constrain the early history of the Local Group and the galaxies therein.

A tale of tails

Brosch, Noah

We present new and archival observations of diffuse, very faint surface brightness features in the multiple galaxy systems NGC5022+NGC5018+MCG-03-34-013, and the Hickson’s Compact Group 098. These consist of optical, near-IR and space-UV imaging and of reprocessed VLA observations. We propose that in the first system we see remains of a disrupted gas-rich dwarf galaxy in the form of ~140 kpc long gas, dust and stars filament, whereas in HCG098 the features represent the remains of a gas-poor dwarf merging with the two brighter galaxies of the group while producing a 170 kpc halo and a 150 kpc long tail. These observations and their interpretation shed light on the issue of dwarf galaxy accretion to build up more massive galaxies.

Faint Dwarf galaxies in nearby WINGS clusters: photometric characterization

Bettoni, Daniela

In the cores of galaxy clusters there is a population of lows-mass stellar systems such as dwarf Early-type galaxies, ultra-compact dwarf galaxies (UCDs) and ultra diffuse dwarf galaxies. We present here the photometric and morphological characterization of this population of objects using deep CFHT images of a sample of clusters belonging to the WINGS survey (0.04<z<0.06).we study="" only="" galaxies="" that="" are="" spectroscopically="" confirmed="" members="" of="" the="" cluster.="" population="" dwarfs="" ranges="" from ="" ~30%="" for="" more="" rich="" clusters="" to ="" ~5-6%="" less="" ones.="" we="" found="" a="" red="" and="" blue="" discuss="" their="" properties="" in="" comparison="" with="" cluster="" characteristics.="" finally="" this="" sample="" compared="" data="" from="" nearby="" as="" virgo="" coma.="" implications="" mechanisms="" formation="" dwarf="" systems="" briefly="" discussed.<="" p="">

Orbital Resonances of the Galactic halo

Schuster, William

 Orbital resonances in the Galactic halo have been studied using a scaled Allen& Santillán (1991) Galactic mass model, which includes a Galactic bar. For the two moving groups of the Galactic halo, G18-39 and G21-22, originally detected by Silva et al. (2012), we find that with an angular rotation speed of the bar of 45-55 km/s/kpc the majority of stars in both groups appear trapped in two resonances over the Galactic plane, generated by the bar and which cross the solar vicinity.    So, in reality these two moving groups are part of stellar supergroups which populate these two resonances.  The position of these two groups in the (U,V) plane (the Bottlinger diagram) can be explained approximately by means of the mean (U,V) field generated by these two resonances crossing the solar vicinity, in contrast with the alternate explanation of Silva et al. (2012) based on the simulations of Meza et al. (2005) which consider that these two groups, seen as two peaks in the U Galactic velocity, have been created by the accretion of a dwarf galaxy by the Milky Way, such as that of Omega Centauri.

The Search for Intermediate Mass Black Holes in Dwarf Galaxy Mergers

Stierwalt, Sabrina

Massive black holes in today's dwarf galaxies offer a unique window into not only the typical masses of early black holes and the properties of the galaxies that host them, but also how these seeds may have formed. Mergers among massive galaxies are observed to fuel central AGN but whether or not this process happens at lower masses in dwarf-dwarf interactions is unknown. I will present the latest results from the TiNy Titans survey of interacting dwarf galaxies to determine whether interacting dwarfs can harbor and fuel their own active massive black holes.

The dynamical impact of satellite galaxies on the Milky Way disc

Just, Andreas

We investigated the interaction of dark matter (DM) subhaloes on the thin disc of Milky Way-like host galaxies by high-resolution re-simulations combining the statistical properties of DM halos from the Aquarius simulations with a live host galaxy in dynamical equilibirum. We have shown that the contribution of DM subhalos to the dynamical heating of the inner disc of the Milky Way is not dominant. However, the impact of DM haloes with a few billion solar masses on disc perturbations like the bar, vertical wiggles and warps is significant. These DM intruders are not able to force a bar to form, but they can trigger or delay bar formation by up to a Gyr, if the galaxy becomes bar unstable. Consequently, from the existence of a (even young) bar one cannot infer a recent interaction event with a satellite galaxy. In contrast, vertically oscillating ring-like wiggles as observed recently in the Milky Way, have a lifetime of roughly 1 Gyr and thus point to a recent pertubation event. Warps of the outer disc survive for a few Gyr or even longer and serve as a cumulative measure of past harassement or merger events of satellite galaxies. The dynamics of the impact of DM subhaloes with respect to the formation and evolution of bars, wiggles and warps will be discussed.

Multiple Absorption Systems in the Lines of Sight to Quadruply Lensed Quasar H1413+1143 As a Probe of the Circumgalactic medium around Dwarf Galaxy

Okoshi, Katsuya

We present the first measurement of differences in MgII absorption strength in three intervening absorbers at redshift z=1.66, 2.068, and 2.097, which are also identified as (sub-)Damped Lyman alpha (DLA) absorption systems, in the four spectra of the quadruply lensed and broad absorption-line quasar H1413+1143, often referred to the “Cloverleaf” from highly spatial resolution and high signal-to-noise (S/N) spectroscopy with an optical multi-mode spectrograph, the Kyoto tridimentional spectrograph II (Kyoto 3DII) on board the Subaru telescope. We find that significant metal absorptions are detected in one and/or more components in the spatially-resolved spectra toward H1413+1143. This suggests that chemical enrichment differs at least on scale of about 10 kpc within the separation of sightlines similarly to the variation of the other metal absorption and HI absorption strengths. Specifically, we find that all systems at z=1.66 and three ones at z=2.068 in the four sightlines are strong MgII systems while only one system at z=2.097 is identified as a strong MgII system. The rest equivalent widths of MgII absorption lines change by factors within 2 for the multiple absorption systems at z=1.66 and 2.068. We will discuss the observed variation of low-ionization absorption strengths in comparison to that of high-ionization ones. Furthermore, host galaxies giving rise to both damped Lyman alpha absorption and the multiple metal absorption lines in the spatially-resolved spectra toward H1413+1143 will be discussed on the basis of highly spatial resolution and high S/N spectroscopy with Kyoto 3DII observation.

Chemo-dynamic analysis of the stellar component of Local Group isolated dwarf galaxies

Taibi, Salvatore

The study of dwarf galaxies is of great importance to understand galaxy evolution at the low-mass end. In the Local Group (LG) the great majority of them are found to be satellites of the Milky Way or M31. The closest ones have been studied in great detail, however it is hard to constrain if their present-day observed properties are mainly caused by internal or environmental mechanisms.In order to minimize environmental effects and gain insights into the internal mechanisms that shape the properties of dwarf galaxies, we are studying some of the LG dwarf galaxies that are found in isolation, i.e. located far beyond the virial radius of the Milky Way and M31. Our sample includes two of the three LG isolated early-type, passively evolving dwarf galaxies (Cetus and Tucana), and a similarly luminous gas-rich, transition-type (Aquarius). We note that the isolated early-type galaxies are of particular interest since they break the morphology-density relation found for the LG, where the early-type dwarfs are generally found to be satellites of the main galaxies, while the late-types are all found in isolation.We present here results from a sizable spectroscopic sample of individual red giant branch stars taken with the VLT/FORS2 instrument for each individual galaxy. The spectra have a resolution of R~2600 and cover the region of the near-infrated CaII triplet, from which we obtain line-of-sight velocities and metallicities ([Fe/H]). The wide-area coverage of our data allows us to obtain information on the large-scale dynamical and chemical properties of the considered galaxies, such as the possible presence of rotation, metallicity gradients, and multiple chemo-kinematic components. Results on the Cetus and Tucana early-types place more stringent constraints on the formation mechanisms that led to their present-day morphology, while the study of Aquarius showed an unexpected kinematic correlation between the stellar and the gas component.

The spatial segregation impact on the star formation histories of nearby dwarf spheroidal galaxies

Makarova, Lidia

Nearby dwarf galaxies are an excellent laboratory to study the processes of star formation, since they are resolved into individual stars, and their structure is relatively simple. At the same time, the role of dwarf galaxies in the formation and evolution of visible structures in the Universe is very significant. In recent years, we have discovered and investigated a number of isolated dwarf spheroidals (dSphs). It is important to get detailed consideration to such the rare objects, since the common recent scenario of dSphs formation suggests that such galaxies are formed due to the interaction between a rotationally supported dwarf irregular galaxy and a MW-sized host galaxy. Then rather isolated dwarfs should be exceptionally irregular. However, we have found a number dwarf galaxies, which are classical spheroidal, and are located in isolation. Using our HST/ACS observations of these objects, we homogeneously measured their star formation histories (SFHs). We determined the star formation rate as a function of time, as well as the age and metallicity of the stellar populations. All objects demonstrate a complex SFH, with a significant portion of stars formed 10-13 Gyr ago. Nevertheless, the stars of middle ages (1-8 Gyr) are presented. In order to understand how the SF parameters influence the evolution of dSphs, we also studied a sample of nearest dSphs in a different environment: isolated (d<2 Mpc); beyond the Local Group (LG) virial radius (but within the LG zero velocity sphere); and the satellites of M31 located within the virial zone (300 kpc). Using archival HST/ACS and WFPC2 observations of the dSphs, we measured their SFHs. A comparative analysis of the parameters obtained give us a possibility to distinguish a possible effect of the spatial segregation on the dSphs evolution scenario.

Schwarzschild model of the Fornax dSph

Kowalczyk, Klaudia

The Fornax dwarf spheroidal galaxy is one of the best studied satellites of the Milky Way. Thanks to its proximity, a convenient position on the sky and high luminosity, large data samples for its resolved population of stars, both photometric and spectroscopic, are available. I will present the outcome of modelling Fornax with the spherically symmetric orbit superposition method, including the derived mass and velocity anisotropy profiles. I will compare our results with those given in the literature and obtained with both full data modelling (applying Jeans or Schwarzschild methods) and simple mass estimators. I will also discuss a possible bias caused by the non-spherical shape of the galaxy and its implications for the final interpretation of the results.

Structure of dark matter haloes of Milky Way satellite galaxies in SIDM universes

Okamoto, Takashi

CDM has some difficulties in explaining the small-scale structure of dark matter halos, such as central density distribution of the dark matter halos of the Milky Way satellites. These problems can be resolved by invoking galaxy formation processes because the central density of low-mass halos can be lowered by strong feedback. This fact alone, however, does not mean that CDM is consistent with observations because galaxy formation processes are tuned to reproduce observations. To observationally discriminate CDM from other dark matter models such as warm dark matter (WDM) and self-interacting dark matter (SIDM), we have to carry out galaxy formation simulations assuming these dark matter models and appropriately tuned galaxy formation processes to reproduce basic observational properties such as the satellite luminosity functions. We have implemented SIDM models by Loeb and Weiner  (2011), of which the interaction cross-section depends on the relative velocity between two SIDM particles. The SIDM subhalos have cored profiles and much less abundant than the CDM subhalos. We report the difference between the structure of the CDM and SIDM subhalos when we tune the baryonic physics to reproduce the observed luminosity function of the Milky Way satellites. 


Marchi, Sebastian

In this article we use structural properties of Milky Way’s outer halo (RG < 25kpc) satellites (dwarf spheroidal galaxies, ultra-faint dwarf galaxies and globular clusters) derived from deep, wide-field and homogeneous data, to present evidence of a correlation in the Sersic index - Effective radius plane for all outer halo satellites. We show that this correlation can be entirely reproduced by fitting empirical relations in the central surface brightness - absolute magnitude and Sersic index - absolute magnitude parameter spaces, and by assuming the existence of two types of outer halo GCs: one of high surface brightness (HSB group), with properties similar to inner halo clusters; and another of low surface brightness (LSB group), which share characteristics with dwarf spheroidal and ultra-faint dwarf galaxies. Given the similarities of LSB clusters with dwarf spheroidal and ultra-faint dwarf galaxies, we discuss the possibility that outer halo clusters also originated inside dark matter halos and that tidal forces from different galaxy host’s potentials are responsible for the different properties between HSB and LSB clusters.

HI Gas component in dwarf galaxies in the view of semi-analytic models

Fu, Jian

In this talk, we will show our recent progress on semi-analytic models of galaxy formation, which mainly focus the HI gas component in low mass galaxies. Our models based on the SAMs codes L-Galaxies and run on the Aquarius haloes and ELUCID halos to study the local dwarf galaxies, and we use the presciprtions related to interstellar surface densities, metallicities and UV back ground field to calculated the HI gas components in ISM. We show that:(1) Our models can fit the HI mass function from ALFALFA to very low mass end, and the low mass end of HIMF is very sensitive to the physical processes in low mass satellites, e.g SN feedback, ram pressure stripping.(2) Our models predict a lot of gas rich low mass dark galaxies, which may offer opportunities for future HI 21cm survey in neary by galaxies by FAST and SKA-1.(3) The tight correlation between HI disk size and HI mass can be extended to very low mass range (MHI~107Msun), we find that is mainly caused by the transition between atomic gas and molecular gas.(4) The minor mergers processes between HI rich satellites and central galaxies contribute a large fraction of HI source in gas accretion.

Stellar and dark halo properties of LAEs: the efficiency of star formation and the origin of diffuse Lya halos

Kusakabe, Haruka

Lya emitters are a representative dwarf galaxy population at high z characterized by strong Lya emission. However, the stellar mass (Ms), SFR, and dark halo mass (Mh) of LAEs have not been estimated with a high enough accuracy to place them in the framework of structure formation. Moreover, the origin of diffuse Lya halos (LAHs) has not been identified in spite of the fact that the Lya luminosity of LAHs is comparable to or even higher than that of the main body of LAEs. To address these issues, we study the stellar and dark halo properties of LAEs using a large sample of z~2 LAEs for which LAH luminosities are available by stacking analysis. We find that while these LAEs are consistent with SFMS galaxies, they have relatively high Ms/Mh and SFR/BAR ratios, implying that LAEs have been converting baryons into stars efficiently in spite of their low Mh. We also find a nearly constant LAH luminosity with Ms and Mh. This suggests that LAHs are caused by scattering of Lya photons in the CGM, not by in situ gas cooling or star formation in satellite galaxies, because the latter two origins predict a roughly linear scaling of LAH luminosity with these masses. When the LAH component is included, LAEs have very high Lya escape fractions reaching ~30-100%, being one dex higher than those of HAEs with the same Ms and E(B-V). Such high escape fractions may be partly due to relatively low gas masses implied from high Ms/Mh ratios, i.e., high efficiencies of star formation, although another Lya source may also be needed in the main body of LAEs.

Star formation and starbursts in dwarfs

Knapen, Johan

We use a representative sample of over 1500 galaxies that has been imaged in the optical and IR in the Spitzer Survey of Stellar Structure in Galaxies to collect information on their star formation rate (SFR), specific SFR, SFR density, gas content, gas depletion time, stellar mass, morphological type, and whether they are interacting. We calculate values for all these parameters normalised to individualised control samples. This allows us to study how star formation in dwarf galaxies behaves when compared to higher-mass galaxies. We also consider how common starburst definitions can mis-classify when confronted with dwarf galaxies.

Starburst Dwarfs: the Super Star Clusters Form at Filament Hubs

Beck, Sara

The ”starburst” in starburst dwarfs is usually in one or a few super star clusters. These young clusters include the most extreme star formation in the local Universe; they hold up to 106M? of stars younger than 5 Myr in a few pc3, and one such deeply embedded cluster can dominate the total luminosity of the galaxy. What triggers the starburst activity? In what environment do these clusters form? How do these intense concentrations of young OB stars interact with their embed- ding clouds? To answer these questions, we use ALMA, the SMA, the JVLAand TEXES (a high–resolution mid-infrared spectrometer) to observe molecules, ions and dust in nearby starburst dwarfs. Typical spatial and spectral resolution are ˜ 5 pc and ˜ 4 km/s . We find that the starforming clouds are hot and dusty, and appear as distinct filaments. In NGC 5253 the bright embedded cluster is accreting a massive filament, and in He 2-10 the young clusters have formed where several filaments meet in a ’hub’. In some galaxies we see ionized gas escaping from the embedded ionized nebulae in slow pressure-driven flows.

Internal properties of dwarf galaxies in the MATLAS survey and variation with environment

Poulain, Melina

The MATLAS project, aimed at studying the outer most regions and surroundings of a complete sample of nearby field Early Type Galaxies, has produced deep multi-band optical images with limiting surface brightness down to nearly 29 mag/arcsec2 in the g band. Such images obtained with MegaCam on the CFHT have optimal conditions (large scale of view, high sensitivity) for dwarf galaxies detection. We have made a systematic survey of the dwarf galaxy satellites located within 153 fields of one square degree each. Based on semi-automatic detection algorithms, we obtained a catalog of 3674 potential dwarf galaxies situated in low density environments. All candidates were visually inspected to exclude likely foreground/background objects or artifacts. Remaining projection effects are partly compensated by the high number statistics. Assuming for the satellites a distance corresponding to that of their host, we derived for all them their basic properties - color, mass, Sérsic index, effective radius, nucleation, morphology - and their variation with environment. We found a large number of dwarf ellipticals, with a significant fraction of nucleated ones, and ultra diffuse galaxies that was unexpected outside the cluster environment.

‘Intriguing’ scaling relations of dwarf irregular galaxies

Iorio, Giuliano

Scaling relations of galaxies represent an important benchmark for cosmological simulations and for theories of galaxy formation and evolutions.  The properties of scaling relations for dwarf galaxies are still not well known due to the large uncertain on the estimate of dwarf properties. In this context, the kinematics of HI discs of dwarf irregular galaxies (dIrrs) represents a fundamental piece of information to explore certain scaling relations. Using robust estimates of the HI disc kinematics for a sample of 17 dIrrs, we present an analysis of three ‘intriguing’ scaling relations. We analysed the Baryonic Tully-Fisher relation and the Radial Acceleration Relation at the very low mass scales traced by dIrrs. We found that the relations found for the galaxies in our sample are compatible with what is found for more massive galaxies in contraposition with what is predicted by cosmological simulations.  Finally, we found a clear correlation between the kinetic energy held in the HI turbulent  motions  and the star formation rate density of the dIrrs. Comparing this relation with the supernova explosions theories,  we found that the turbulence in the HI discs can be sustained by the star formation activity assuming an average efficiency of about 30% in transferring the supernova explosions energy into the ISM.The results of this work represent relevant tests for galaxy formation theories and for cosmological simulations, moreover, they reveal the fundamental role of the star formation feedback in feeding the turbulence in the ISM.

Using Inhomogeneous Chemical Evolution to Model Dwarf Galaxies

Jordan, Chris

We use an inhomogeneous chemical evolution (i-GEtool) code to model the dwarf spheroidal galaxy, Draco. Using i-GEtool as opposed to traditional chemical evolution models allows a natural dispersion to occur within the output data, thus mimicking observations. We tune our model to simulate the Draco system using the metallicity distribution function and star formation history. We investigate the alpha-element abundance distributions, comparing and contrasting different stellar yields to find a best fit to observational data. Lastly we examine methods used for calculating gas outflow in models.we confirm that the use of different stellar yields sets can change GCE results. For instance, the NuGrid yield set has problems reproducing the high [alpha/Fe] observations whereas the yields from do not reproduce the low [alpha/Fe] results. We use a new method in inhomogeneous codes to model outflows, allowing supernovae type-II to expand beyond the radius of Draco, making outflows self-consistent and more similar to current hydrodynamic models. Our outflow method was found to imply a high ratio of star formation rate to outflow rate, i.e. mass-loading, factor of ~15.

Exploring the Radio Continuum vs. Star Formation Rate Relation in Nearby Dwarf Galaxies

Hindson, Luke; Brinks, Elias

The source of the radio continuum (RC) emission from normal star forming galaxies is directly linked to massive stars and can be used as an indicator of the star formation rate (SFR). This is seen observationally in the RC-SFR relation. This relationship may provide a robust, unbiased, and perhaps most importantly an extinction free tool for characterising the SFR in both the Local Universe and at high redshift in upcoming radio surveys with instruments such as the VLA, LOFAR, and SKA. In an effort to calibrate the relationship and understand its physical origin we have undertaken a sensitive, multi wavelength, high-resolution study using the VLA of a sample of 40 nearby dwarf galaxies (a proxy for early type galaxies) taken from the LITTLE THINGS survey. By combining our VLA observations with ancillary data including H-alpha, 24um, and the FUV we separate the radio continuum emission into its thermal and non-thermal components and compare these to the SFR. We use these results to calibrate the RC-SFR relation on scales from 200 to 700 pc, explore the equipartition magnetic field properties of the galaxies, and the intrinsic scatter in the RC-SFR relation.

A numerical study on the distribution of the tidally stripped matter of the Milky Way satellites

Mazzarini, Matteo

I address the phase-space distribution of the matter stripped from the Milky Way (MW) satellites. From a first N-body test of MW-satellite interaction performed with Gadget 4 (a code from Springel et al., in prep.), I find that the baryonic matter stripped from a satellite has a narrow distribution around the density center of the satellite, while the dark matter (DM) component is more spread around it. Based on this result, I perform a statistical analysis of high-resolution, pure N-body simulations of MW-satellites interaction already run in Moetazedian & Just (2016) following the Aquarius DM-only cosmological simulations (Springel et al. 2008). Second, performing N-body simulations with Gadget 4, I substitute the Aquarius satellites with hybrid baryonic-and-DM satellites (Macciò et al. 2017, Frings et al. 2017) in order to address a similar analysis, also looking at the difference between the deposit of baryonic and dark debris in the MW environment. Preliminary results indicate more stripping happening for DM rather than for baryonic matter. Also, these results suggest on average similar radial density fractions of stripped DM in both simulation sets and a higher density fraction of stripped baryonic matter than DM in the innermost halo. I plan to look at the time required to destroy the nuclei of the satellites. Further simulations are planned, with hyrodynamics and feedback implemented in order to quantify their impact on the stripping process and on the distribution of the streams.

Nucleated dwarf galaxy population in the Fornax galaxy cluster

Ordenes, Yasna

We present the analysis of the nucleated dwarf galaxy population in the central regions (= 350 kpc) of the Fornax galaxy cluster. The galaxies and their nuclei are studied as part of the Next Generation Fornax Survey (NGFS) using optical imaging obtained with the DECam mounted at Blanco/CTIO and near-infrared data obtained with VIRCam at VISTA/ESO. We decompose the nucleated dwarfs in nucleus and spheroid, after subtracting the surface brightness profile of the spheroid component and studying the nucleus using PSF photometry. In general, nuclei are found in a narrow color range, consistent with colors of confirmed metal-poor globular clusters (GCs), and with significantly smaller dispersion than other confirmed compact stellar systems (CSSs) in Fornax. We find nucleus masses in the range 4.8=log(M/Msun)=7.3 and detect a bimodal distribution with peaks located at log(M/Msun)~5.4 and ~6.3. We show that the two nucleus-mass sub-populations have different stellar population properties, where the more massive nuclei are older than ~2Gyr and have metal-poor stellar populations (Z=0.02Zsun), while the less massive nuclei are younger than ~2Gyr with higher metallicities in the range 0.02<z zsun="1." we="" find="" that="" the="" nucleus="" mass="" (m_nuc)="" vs.="" galaxy="" (m_gal)="" relation="" becomes="" shallower="" for="" less="" massive="" galaxies="" starting="" around="" 108="" msun.="" consequently,="" ratio="" ?="" (m_nuc="" m_gal)="" shows="" a="" clear="" anti-correlation="" with="" m_gal.="" ?-m_gal="" correlation="" exhibits="" two="" different="" regimes;="" both="" regimes="" reach="" maximum="" ?~10%="" at="" lowest="" and="" highest="" masses.="" test="" current="" theoretical="" models="" of="" nuclear="" cluster="" formation="" they="" cannot="" reproduce="" these="" observed="" trends.="" however,="" likely="" mixture="" in-situ="" star="" star-cluster="" mergers="" seems="" to="" be="" acting="" during="" growth="" over="" cosmic="" time.<="" p="">

Stellar feedback powering star-forming complexes in the Magellanic Clouds

Hamann, Wolf-Rainer

Clustered populations of massive stars have a big impact on their environment. They can create large structures like supergiant shells (SGSs) and superbubbles of shocked, X-ray emitting gas.  The formation of such structures is the direct result of stellar feedback  from the massive stars via strong ionizing radiation, stellar winds, and supernovae.Only detailed spectroscopic studies of the massive-star population can reveal the mechanisms that power their environment.  We performed exemplary studies on star-forming regions  in the supergiant shell SMC-SGS1 in the Wing of the SMC and in the complex  N206 in the LMC, which encloses an X-ray  'superbubble'.We obtained many hundreds of spectra with VLT FLAMES  of the massive star populations associated with each of the two mentioned complexes. Quantitative spectroscopic analyses were performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code, yielding  the stellar and stellar-wind parameters. The PoWR models then provide the ionizing flux and the mechanical feedback from each massive star.  Based on the total stellar feedback, the energy budget of the complexes is quantified and discussed. The star formation history is reconstructed from the distribution of stellar ages.The talk is focusing on massive stellar populations at different metallicities, obviously undergoing different modes of current star formation. The talk will highlight the role of feedback for the evolution of these dwarf galaxies.

First X-ray look at Green Peas

Ehle, Matthias

Cosmic reionisation of the Universe played an important role in the galaxy formation and their observability. The source of the ionising radiation is, however, not yet clearly determined: it could be due to strong AGN activity or due to tremendous star formation. Whether ionising radiation from high star-forming galaxies can escape to the intergalactic medium is being discussed.Green Peas represent a class of compact high star-forming galaxies that have recently shown signatures of the escape of the ionising flux. We present first measurements of Green Peas in the X-ray domain to constrain their flux at high energies. We found that the X-ray flux is about an order of magnitude larger than expected from the standard relation between the X-ray flux and the star formation rate. Our results indicate that Green Peas galaxies produce more high-energetic flux than other starforming galaxies, and can therefore be considered as sources with potentially large and significant ionising radiation escape.

Tidal fields and mass estimate of dSphs: the case of Sculptor

Iorio, Giuliano

The study of the dynamics of dwarf galaxies is one of the essential keys to understand their formation and their evolution. The dwarf spheroidal satellites of the Milky Way are close enough to be explored in details. In particular,  it is possible to estimate the total matter content using the kinematics of the stars.  The interpretation and the modelling of these data rely on equilibrium models in which we assume that the stellar kinematics is a genuine tracer of the galactic potential.  However, these objects are orbiting in the tidal field of the Milky Way and it could be possible that the velocity dispersion is inflated by stripped stars along the line of sight. Therefore, the estimate of the dark matter content of these objects could be biased. In this talk, I will present detailed N-body simulations focused on the reproduction of the properties of the Sculptor dwarf spheroidal. Using the most recent and robust measurements of the proper motion of Sculptor and conservative assumptions on the Milky Way mass, we tuned the initial properties of the N-body realisation to reproduce the observed properties we see today.  Finally, we analysed the final snapshot of the simulations as is done for real data.We found that, even in the worst case (closest epicentral passages), the kinematics of the stars in Sculptor is not affected by the tidal field of the Milky Way. Therefore, we conclude that the method commonly used to retrieve the mass in dwarf spheroidals are capable to return robust estimates of the total matter content of Sculptor.

AGN and Star Formation Feedback in Active Galaxies

Clavijo bohórquez, William Eduardo

Large scale, weakly collimated out?ows are very common in some active galaxies. In complex systems, where (SF) coexists with an active galactic nucleus (AGN), like in Seyferts, and probably dwarf galaxies and ULIRGs, it is unclear yet the relative role that the AGN and the SF play in the driving of the out?ows, which frequently exhibit persistent high-speed cold structures.In this work we present high-resolution 3D hydrodynamical and magnetohydrodynamical (MHD) numerical simulations of the formation of these out?ows considering both the feedback from the AGN outflow (with opening angles between 0 and 10 degrees), and the supernovae (SNe)-driven wind (including the contributions of type I and II).The results indicate that the presence of an AGN wind with large opening angles and of magnetic fields substantially a?ect the evolution of these systems. While magnetic ?elds help to preserve dense structures of the ISM which are swept by the SN and AGN outflows, the large-opening angle AGN wind may temporarily exhaust the gas near the nuclear region (thus extinguishing star formation) and account for the highest speed features in the wind at kpc scales, although these are not as cold as required by the observations. The SN-driven wind is the main responsible for the mass-loading of the outflows, while the AGN wind accounts for the highest speed component which reaches velocities up to a few 10,000 km/s. Finally, the implications of these findings in the framework of dwarf galaxies evolution will be also discussed.

Unusual LSB dwarf companion of the interacting galaxy NGC4656

Saburova, Anna

We studied the dwarf low surface brightness galaxy with the enhanced UV brightness, NGC4656UV, belonging to the interacting system NGC4631/56. Regular photometric structure and relatively big size of NGC4656UV allows us to consider this dwarf galaxy as a separate group member rather than a tidal dwarf. Spectral long-slit observations were used to obtain the kinematical parameters and gas-phase metallicity of NGC4656UV and its companion - interacting galaxy NGC4656. Our rough estimate of the total dynamical mass of NGC4656UV allowed us to conclude that this galaxy is the dark-matter dominated LSB dwarf or ultra-diffuse galaxy. Young stellar population of NGC4656UV, as well as strong local non-circular gas motions in NGC4656 and the low oxygen gas abundance in the region of this galaxy adjacent to its dwarf companion, give evidence in favour of the accretion of metal-poor gas on to the discs of both galaxies.

The Next Generation Fornax Survey (NGFS): The Central Dwarf Galaxy Population

Eigenthaler, Paul

We present a photometric study of the rich dwarf galaxy population in the core region (? rvir/4) of the Fornax galaxy cluster based on deep u'g'i' photometry from the Next Generation Fornax Cluster Survey (NGFS). All imaging data were obtained with the Dark Energy Camera mounted on the 4-meter Blanco telescope at the CTIO. We identify 258 dwarf galaxy candidates with luminosities -17 ? Mg' ? -8 mag, corresponding to typical stellar masses of 9.5 ? log M? /M? ? 5.5, reaching ~3 mag deeper in point-source luminosity and ~4 mag deeper in surface-brightness sensitivity compared to the classic Fornax Cluster Catalog. Based on the present NGFS data and the comparison with other stellar systems from the literature, we discuss the implications of our findings for galaxy stellar mass assembly over a stellar mass range of  5?log(M?/M?)?12. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be clearly identified: i) dwarf galaxies assemble mass inside the half-mass radius up to log M? ˜ 8.0, ii) a regime of isometric mass assembly in the range 8.0 ? log M?/M? ? 10.5, and iii) massive galaxies assemble stellar mass predominantly in their halos at log M? ˜ 10.5 and above.

Catalog & Atlas of the LV Galaxies

Kaisina, Elena

We present a database of galaxies in the Local Volume ( having individual distance estimates within 11 Mpc or corrected radial velocities VLG < 600 km s–1. It collects data on the following galaxy observables: angular diameters, apparent magnitudes in far-UV, B, and Ksbands, Ha and HI fluxes, morphological types, HI-line widths, radial velocities, and distance estimates. Also contains a consolidated set of optical images of all the galaxies from the SDSS and DSS surveys and Ha images of galaxies that were observed with the 6-m BTA telescope. The latest version of the Updated Nearby Galaxy Catalog (UNGC) (Karachentsev et al. 2013) contains 869 objects, now in the database more 1150 objects. We present the some main dependencies describing the updated sample LV galaxies: Hubble flow, distribution galaxies according to their distance estimates and on the sky, relation between the absolute magnitude, Holmberg diameter, and rotation velocity et al.

A Newly Discovered Reservoir of Dwarf Galaxies in the Centaurus A Group

Taylor, Matthew

Recent years have seen an acceleration in the discovery rate of dwarf galaxies in the Local Universe. The subsequent unveiling of coherent satellite phase-space structures like groups and planes has led to a renaissance in the study of low-surface brightness dwarf galaxies, including their utility in near-field cosmological studies. In an effort to push this field further, optical u’g’r’i’z’ imaging of 22 deg^2 centered on the nearby giant elliptical galaxy NGC5128, as part of the “Survey of Centaurus A’s Baryonic Structures” (SCABS) campaign, has been searched for new dwarf galaxies in the Centaurus A group. We will present first results of the stellar mass and stellar population properties for several dozens of promising new candidates, including several dwarf pairs appearing within a few pc in projection that may indicate physical associations. These new dwarf galaxies extend the size-luminosity relation toward fainter total luminosities and smaller sizes for known dwarf galaxies outside the Local Group, and are broadly consistent with the properties of nearby dwarf spheroidal galaxies. Altogether, these new results show NGC5128 to be the host of a large reservoir of low-mass dwarf galaxies that is at least as rich as that of the Local Group and is ripe for detailed follow-up observations.

The Dwarf Galaxy–Environment Connection as seen by the Next Generation Fornax Survey

Puzia, Thomas H.

The Next Generation Fornax Survey (NGFS) is a panchromatic imaging campaign that covers the virial sphere of the Fornax galaxy cluster in optical (u’g’i’, using DECam@CTIO) and near-infrared filters (JKs, using VIRCam@VISTA). The survey targets all baryonic structures down to point-source luminosities typical of globular clusters and reaches surface brightness limits deep enough to detect ultra-diffuse and LSB dwarf galaxies. Here we present the first map of the spatial distribution of a rich system of more than 600 dwarf galaxies inside half of Fornax' virial radius that demonstrates, for the first time, the transition from the dense central dwarf galaxy population to the less dense outer environment. We present strong evidence for spatial substructure in the dwarf galaxy distribution and show that dwarf galaxies are significantly clustered on spatial scales less than ~100 kpc. In the context of overall dwarf galaxy properties, we discuss our findings in relation to other ongoing surveys of the local universe led by our team.

Atlas of Ha-images for five hundred nearest dwarf galaxies

Kaisin, Serafim

Results of mass imaging nearby dwarf galaxies in emission Ha-line and red continuum with the 6-m BTA telescope are available via the address: The sample of dwarfs limited by a distance of 11 Mpc contains about 500 objects. Their Ha-fluxes are used to derive integrated and specific star formation rates of the galaxies. We evaluate the consistency between star formation rates obtained from our Ha-survey and GALEX far-ultraviolet survey. We fix a systematic rise of the ratioSFR(FUV)/SFR(Ha) with the decreasing stellar mass of dwarf galaxies.

MAPPINGS photoionization models of H II regions in dwarf irregular galaxies

Bensch, Katarzyna

Star-formation has a direct influence on chemical abundances of galaxies. Gas-rich dwarf irregular galaxies (DIGs) are less chemically evolved and therefore are great laboratories for detailed studies of chemical evolution. Their star-formation histories are simpler than those of massive galaxies. Especially isolated DIGs are important sources for understanding star-formation. They have been formed and evolve far from dense cluster centres and the gravitational influences of massive companions. The isolation allows us to study star-formation that originates purely from evolutionary processes of the pristine IGM in galaxy environments. We use Integral Field data to study 7 metal-poor DIGs with VLT/VIMOS and 13 isolated gas-rich DIGs from the SIGRID sample obtained with WiFeS. The H II emission suggests ongoing star-formation for the past 5 Myr. Metallicity estimates for HII regions of DIGs are one of the most important tools  towards an understanding of galaxy evolution since those studies require a precise metallicity calibration. We derive theoretical models using the MAPPINGS photoionization modelling code to predict theoretical emission line ratios at different values of metallicity and ionization parameters. The detection of multiple emission lines of H, O, N, Ne, He, S, and Fe allows us to use and compare different line-ratio grids to study the metallicity of the different HII regions. We investigate their resolved chemical composition, paying special attention to the metallicity-age connection. We discuss the problems arising from the limitations of simple geometric models and depletion of elements onto dust. The spatially resolved star formation history is consistent with the predictions from the models over the several hundred million years.

The effect of ram pressure on Dwarf Galaxies

Steyrleithner, Patrick

Ram-pressure stripping (RPS) is a well observed phenomenon of massive spiral galaxies passing through the hot inter-galactic medium of galaxy clusters. Since the dominant morphological type of dwarf galaxies (DGs) in clusters is provided by the gas-free early-type DGs these must have suffered gas evacuation already long ago. This process can, however, not be observed at DGs in the denser cluster region, because for low-mass DGs it must happen already in the outskirts of clusters. While this was difficult for a long time, since the last decade such DGs in ram-pressure transformation are in fact observed by a few objects in close-by galaxy clusters.Although for DGs this RPS process sounds analytically simple, a wide range of various structures is observed from the total gas evacuation to partial gas stripping, respectively. In contrast to the RPS in massive spiral galaxies star formation (SF) occurs in stripped gas clouds of DGs. In addition, SF seems to be partially enhanced by the ram pressure exerted on DGs. Moreover, some early-type DGs within clusters contain blue cores, witnessing recent SF, or could even retain dense gas in their centers.From all these facts several questions must be addressed, as e.g., when, where, and how the gas is stripped-off from DGs, how the interstellar medium (ISM) in DGs is affected by the ram pressure, how gas-rich DGs are already influenced when they move through low-density inter-galactic gas, and further more.By numerical simulations of the RPS acting on DGs, applying the massively parallel AMR code FLASH, we aim at answering the above-mentioned questions and at investigating the gas loss by ram pressure, its effect on the gas within DGs, e.g. by compression, and on the SF in the retained ISM and in the stripped gas clouds.For this, we not only compare the evolution of RPS-affected DGs with models of isolated DGs, but also discuss the physical causes that either trigger or prevent SF in the stripped-off clouds.

HST Proper Motions of Dwarf Galaxies in the Local Group

Sohn, Tony

The universe evolves hierarchically with small structures merging and falling in to form bigger structures. Due to its proximity, the Local Group (LG) is the best place to study these hierarchical processes in action. Stellar systems in the LG have therefore become the benchmark for testing several aspects of cosmological theories. Despite the advancements in both observational and theoretical grounds in the past decade or so, many fundamental properties (e.g., total mass and mass profiles) of the LG galaxies and their satellites remain poorly constrained primarily due to the limited information on their transverse motions. Our HST studies are making significant progress in this field by measuring proper motions with unprecedented accuracies. I will present our past and ongoing HST projects for measuring absolute proper motions of dwarf galaxies in the Local Group. I will also discuss the synergy between HST and Gaia as astrometric instruments in the coming years.

The Lifecycle of Dust and Metals in Low-Abundance Galaxies

Hirschauer, Alec

I will discuss the recent discovery of the extremely metal-poor star-forming galaxy Leoncino (~2% solar), among our most promising early-Universe analogues to date, and whose discovery heralds a boom in finding additional similar low-metallicity specimens.  Studies of such nearby low-abundance galaxies reveal the importance of the effect of chemical composition on star formation and the lifecycle of dust and metals during the peak epoch of star formation in the Universe.  I discuss plans to study the lifecycle of dust and metals with JWST GTO observations of the low-abundance star-forming galaxy NGC 6822 and the extremely metal-deficient blue compact dwarf galaxy I Zw 18.  In preparation for these observations, I am investigating the dusty stellar populations in NGC 6822 including the dust-producing stars (e.g., asymptotic giant branch stars) and young stellar objects.

Serendipitous discovery of a pair of faint dwarf galaxies

Makarov, Dmitry

In framework of the study of the distribution and peculiar motion of galaxies in the Local Volume with Hubble Space Telescope we discovered a physical pair of dwarf galaxies with the absolute magnitudes of MV=-13.3 and -9.4 mag. We determined the distance to this pair of 9.2 Mpc using the tip of the red giant branch. The projected separation between the galaxies in pair is only 3.9 kpc. The existence of such systems of dwarfs is not unusual.  On a scale of 3 Mpc most dwarfs are associated with either a luminous group or associations of dwarf galaxies. The groups of dwarfs where both components have the luminosity lower than  the Small Magellanic Cloud form a significant population of all groups on the scale of 40 Mpc. The newly discovered system of dwarfs is one of the faintest known groups of galaxies.

Abundance determinations in two H II regions in the dIrr galaxy Leo A

Pena, Miriam

In this work, we present  chemical abundance determinations of two H II regions in the dIrr galaxy Leo  A, from GTC OSIRIS long-slit spectra. Both regions, which are the brightest HII in this galaxy,  seem to be ionized by stars later than O9 spectral type. In the first H II region, we were able to use the direct method, by measuring the electron temperature  with the  [O III] ??4363/5007 line ratio. For the low-ionized species, an electron temperature derived from the formula by Campbell et al. (1986, MNRAS, 223, 811) was used. Ionic abundances of O+2, O+, N+, and S+ were determined. O, N and S total abundances were calculated using literature ICFs for each element. Abundances by using strong-line methods were also determined, with similar results. For the second H II region, O and N abundances were calculated using strong-line methods. It is confirmed that Leo A in a very low metallicity galaxy, with 12+log O/H = 7.4, log N/O = –1.6, log S/O = –1.1.

Envidence for discrete star formation events in the Small Magellanic Cloud based on 6.5m Magellan Telescope observations

Strantzalis, Achilles

The Small Magellanic Cloud (SMC) is a nearby gas rich dwarf irregular galaxy and interacts both with its neighboring Large Magellanic Cloud and with the Milky Way. Due to its relatively small mass (~ 10-2 MMW ) and inter-galaxy interactions, it has an interesting star and cluster formation history as well as a complex geometry. The SMC presents us with a unique opportunity to study in detail quenching as seen from stellar populations and galactic archeology, as well as the effect of environmental processes (interaction with the LMC and the Milky Way) on star formation processes. With the 6.5m Magellan Telescope at the Las Campanas Observatory in Chile we have acquired multi-filter observations (B, R, I) in four 0.44o fields covering the entire area of the main body of the SMC, yielding accurate photometry for 1,068,893 stars down to ~24th magnitude, with a spatial resolution of 0.201 arcsec/pixel. Colour-magnitude diagrams and luminosity functions (corrected for completeness) have been constructed, yielding significant new results that indicate at least three discrete star formation events over a period from 0.1 to 4 Gyr ago.Additionally, exploiting the high spatial resolution and large extent of this survey we have applied an automated statistical technique in order to identify star clusters (thus allowing verification of the cluster nature of previously published clusters and the discovery of new ones) and study their characteristics (structural parameters and ages).

The massive stars population of IC 10

Corral, Luis

Metal-poor massive stars are key to understand star formation and feedback process in the past Universe, extreme events like SLSN and GRBs, and possibly the properties of the First Generation of stars. The dwarf irregular galaxies of the Local Group make a large reservoir of these objects, with the advantage that their physical properties in various environments can be studied in detail.We present a catalog of massive stars and OB associations in IC10. We have identified 529 candidate massive stars meeting the photometric criteria that we have proven successful in IC1613 and Sextans-A. Our friends-of-friends clustering algorithm has detected 26 associations with 3 or more members, whose age spans from log(age)=6.19-7.05 dex. This census is particularly interesting as IC10 is currently undergoing a starburst phase, and it makes way to study metal-poor massive stars in the first such environment beyond the Magellanic Clouds.

Constraints on the warm dark matter mass using the Milky Way satellite galaxies

Kang, Xi

Studying the very inner structure of faint satellite galaxy requires very high-resolution hydro-dynamical simulations with realistic model for star formation, which is beginning to emerge very recently. In this work we study the  kinematics of satellite galaxies in the Milky Way using an analytical description. Our aim is to investigate their constraints on the nature of dark matter,namely cold dark matter and warm dark matter. We use a Monte-Carlo method to produce merger trees of Milky Way mass halos and a semi-analytical model to produce visible stars in the satellite galaxies. We consider a few important processes which can significantly affect the satellite kinematics. The first is the reduction of dark matter halo concentration in the warm dark matter model. The second is the baryonic feedback which can induce a flat inner profile with a dependence on the star formation efficiency in the satellite galaxy. The third is the tidal stirring which can further reduce the satellite velocity dispersion. Compared to previous studies, our model is firstly tuned to fit the stellar mass of satellites, thus they have correct star formation efficiency and associated inner density profile. We show that in the CDM model the baryonic feedback effect alone can reduce the satellite velocity dispersion to agree with the observation, and a maximum of 30\% reduce in satellite velocity dispersion by tidal heating is allowed. Without tidal stirring, the WDM model with dark matter mass m_s < 3.5 keV is excluded and a strong tidal stirring can even rule out model with m_s < 10 keV. Our results indicate that current favored WDM model with m_s ~  a few keV is bad for the too-big-to-fail problem, and conversely, it leads to a too-diffuse-to-sustain problem.

Formation History of Binary Clusters in the Large Magellanic Cloud

Priyatikanto, Rhorom

Among tens of dwarf galaxies in the local vicinity, Large Magellanic Cloud (LMC) is known as the prototype of Magellanic Irregulars which is rich in gas and star formation. Global history of star or cluster formation in the LMC has beed the center of interest in several studies as it is thought to be influenced by tidal interaction with the Small Magellanic Cloud (SMC) and even the Milky Way. The last episode of close encounter between LMC and the Milky Way is believed to increase the velocity dispersion and probability of collision among molecular clouds which in turn induce formation of new stellar systems. With the right input of kinetic energy, formation of substructure within the system is possible and primordial binary cluster with appealing dynamical behaviour might be formed.In this study, we focus on the formation history of the LMC deduced from age distribution of its star clusters. In relation with the study of binary star clusters in this dwarf galaxy, the apparent binary fraction (e.g. percentage of cluster pairs) in different epoch are calculated and analyzed.From the established distributions, it can be deduced that the binary clusters tend to be young (~100 Myr) while their locations coincide with the locations of star forming complexes. There is an indication that the binary fraction increases as the rise of star formation rate in the last millions years. In the LMC, the increase of binary fraction at t = -100 Myr can be associated to the last episode of close encounter with the Small Magellanic Cloud at t = -150 Myr. This observational evidence supports the theory of binary cluster formation through the fission of molecular cloud where the encounter between galaxies enhanced the clouds velocity dispersion which in turn increased the probability of cloud-cloud collisions that produce binary clusters.

Dark Memories of the Past: Discovery of Ultra-Diffuse Objects around NGC 1068

Tanaka, Ichi

NGC 1068 is one of the most famous Type-2 Seyfert galaxies. Due to its close vicinity to us, the galaxy has played an important role for a unified model of AGNs. We have searched for a sign of the past dynamical disturbance event on the galaxy using deep and wide optical imaging data by the Subaru Telescope. The data taken by Hyper Suprime-Cam as well as the archived data by Suprime-Cam reveal several interesting faint outer structures of the galaxy, most of which were never reported before. We discover three large (re=3~5.5kpc), extremely diffuse objects (UDOs) within 45kpc from the center of NGC 1068. We suggest that two of these UDOs are actually a part of a large loop-like structure surrounding NGC 1068. Such an extremely faint loop or stream is the direct evidence for a past minor merger event. The other UDO has a distorted morphology, suggesting that it is under the influence of strong tidal interaction. Furthermore, we have identified two smaller and very diffuse (µ0,r >25 mag arcsec-2) dwarf candidates within ~140 kpc from NGC 1068. We speculate that these ultra-diffuse dwarfs could be the Tidal Dwarf Galaxies related to the mass assembly of NGC 1068 long time ago. We also detect an asymmetric outer one-arm structure emanated from the western edge of the outermost disk of NGC1068 together with a ripple-like structure at the opposite side. These structures are also expected to arise in a late phase (up to several billion years ago) of a minor merger, according to numerical simulations. We discuss about the possible link between our discovery and the current AGN activity.

Testing cosmology with the phase-space distribution of satellite galaxy systems

Pawlowski, Marcel

Both the Milky Way and the Andromeda galaxy are known to host highly flattened planes of satellite galaxies. These display coherent kinematics, which is consistent with many of their satellite galaxies co-orbiting along the structures. Comparisons to cosmological simulations revealed that these planes of satellite galaxies are in severe tension with expectations based on the ?CDM model. Other phase-space correlations that have been found to be (at the very least) puzzling include the accretion of satellite dwarf galaxies in pairs or groups, the apparent overabundance of backsplash galaxies around the Milky Way, and the lopsidedness of the Andromeda satellite galaxy system. Due to the intrinsic difficulty of observing faint satellite galaxies around more distant hosts, determining their 3D positions and measuring their kinematics, these correlations have thus far been predominantly studied in the Local Group. This lead some to dismiss the planes of satellite galaxies problem by arguing that the Local Group happens to be a statistical outlier in a ?CDM universe. I will discuss successes in expanding such studies to more distant host galaxies. This includes recent results on the kinematics of the satellite galaxy plane around Centaurus A, and the first comparison to ?CDM of the pronounced signal of lopsidedness that has been found in stacked satellite galaxy systems around host galaxy pairs in the SDSS survey. I will discuss how these satellite phase-space correlations compare to expectations based on ?CDM simulations, and whether there is evidence that the inclusion of baryonic processes in cosmological simulations can alleviate the existing tension.

Evolution of dwarf galaxies in a semi-analytic galaxy formation model

Nagashima, Masahiro

Dwarf galaxies are sensitive to some physical processes such as supernova feedback in galaxy formation owing to their shallow gravitational potential wells, therefore, they provide constraints on galaxy formation.  We analyze formation and evolution of dwarf galaxies by using our own semi-analytic galaxy formation model, New Numerical Galaxy Catalog (?2GC), in which we model galaxy formation with many physical processes such as gas cooling and heating, star formation, supernova and AGN feedback, formation of supermassive black holes, galaxy mergers, starbursts, and stellar population synthesis within dark matter halos based on the cold dark matter model of the Universe.  The model is combined with very high-resolution N-body simulations that can resolve the Jeans scale after cosmic reionization, therefore we can be almost free from resolution-dependent rsults.  We have found that our model succeeds in reproducing many observations such as luminosity functions.  In this poster, we extend our analysis towards dwarf galaxies.

Environmental dependence of surface brightness profile types of dwarf galaxies

Lee, Youngdae

We investigate surface brightness profiles (SBPs) of dwarf galaxies in field, group, and cluster environments. Using images from the Korea Microlensing Telescope Network (KMTNet) Supernova Program (KSP) for the NGC 2784 group and SDSS for the Virgo cluster, SBP types are classified into profiles with single exponential (Type I), double exponential (Type II and Type III). Type II and Type III have smaller and larger outer sizes than inner sizes, respectively. SBP types of field dwarfs are compiled from a previous study. The distributions of SBP types are different in three environments. Common SBP types of the field, the NGC 2784 group, and the Virgo cluster are Type II, Type I and II, and Type I and III profiles, respectively. After comparing sizes of dwarfs in different environments, we suggest that since sizes of some dwarfs are changed due to the environmental effects, SBP types are able to be transformed. It makes that the distributions of SBP types in three environments are different. We discuss possible environmental mechanisms on the transformation of SBP types.

Morphology of stellar populations in the Magellanic Clouds from the VMC Survey

El Youssoufi, Dalal

Located at approximately 50 and 60 kpc, the Magellanic Clouds represent the nearest interacting pair of galaxies to the Milky Way. Due to their proximity to our own galaxy, resolved stellar populations and ongoing star formation, the Magellanic Clouds have been targets of intensive research for many years, making them a rather useful laboratory for studying galaxy interactions in a near-field cosmological context. Their morphology, dynamics, and evolution are highly complex and must have been heavily influenced by their interaction with each other as well as with the Milky Way. Tidal forces caused structural changes in the galaxies and so the study of their morphology and structure is important to understand the effect of these interactions. Traced by different stellar populations, the morphologies of the Magellanic Clouds show different properties, different tracers and methods also yield centres that are not mutually consistent.The VISTA near-infrared survey of the Magellanic System (VMC) offers the deepest YJKs band photometry across the Magellanic Clouds up to date, going all the way down to Ks=20.3 (Vega) at S/N=10 with a sensitivity corresponding to the bottom of the red giant branch population. We are using the VMC to investigate the spatial distribution of stellar populations of different ages across the Magellanic Clouds. We also determine the centroids of each stellar population. In this contribution, I will present the result of these studies that allow us to trace substructures possibly related to the interactive history of the Magellanic Clouds.

Subaru Hyper Suprime-Cam Survey for the Local Group Dwarf Galaxies: Ursa Minor

Komiyama, Yutaka

We have carried out a wide and deep imaging survey for Local Group dwarf galaxies using Hyper Suprime-Cam (HSC) which is a 1 Giga pixel CCD camera with 1.5degrees field of view attached to the prime focus of the 8.2-m Subaru Telescope. The high spatial resolution (0.4 arcsec for the best condition, 0.67 arcsec for median) and high sensitivity provided by the Subaru Telescope on Maunakea, Hawaii makes HSC the most powerful instrument for exploring the Local Group galaxies with large apparent sizes. The survey data are used for the target selection of the future Prime Focus Spectrograph survey which is planned to start in 2021.In this presentation, we show the result for the dwarf spheroidal galaxy Ursa Minor (UMi) for which HSC covers out beyond the nominal tidal radius down to ~25 mag in i-band, which is ~2 mag below the main sequence turn-off point. The structure of UMi is investigated for individual stellar component such as red-giant branch stars, blue horizontal branch stars, etc. The structural parameters are estimated and the tidal radius is suggested to be larger than those estimated by the previous studies. The fraction of binary stars of UMi is investigated from the morphology of the main sequence following the method described in Sollima et al. (2007) and Milone et al. (2010). The CMDs of binary systems can be calculated by making use of the isochrone of the representative stellar population (i.e., age and metallicity), the initial mass function, and the binary mass distribution of the system. By comparing the simulated CMDs of different binary fractions with the observed CMD, the fraction of binary systems in UMi is estimated to be ~0.4. The value is consistent with those estimated for the other Local Group dwarf spheroidal galaxies based on the radial velocity measurements, but slightly higher than those derived for the most Galactic globular clusters by the same method.

Dwarf Galaxies of the NGC 2784 Galaxy Group Newly Discovered in KMTNet Supernova Program

Park, Hong Soo

We present the first study on the faint dwarf galaxies in nearby galaxy groups detected in the KMTNet Supernova Program. Our presentation shows the result of BVI surface photometry of 38 dwarf galaxy candidates discovered in deep stack images of ~30 square degrees centered on the NGC 2784 galaxy group. The detection limit in the surface brightness is about µV=28.5 mag/arcsec2 and the faintest central surface brightness is µ0,V= 26 mag/arcsec2. The dwarf candidates have absolute magnitudes brighter than MV = -9.5 mag and effective radii larger than 200 pc assuming they are at the distance of NGC 2784 (d~10 Mpc). Their radial number density decreases exponentially (or with power index, a=-1.3) with distance from the center of NGC 2784. Beyond radius of 0.5 Mpc, the density profile flattens and we estimate the background contamination is about 15%. The mean color, <(B-V)0>=0.7, and Sérsic structural parameters of the candidates are consistent with those parameters for the dwarf galaxies of other groups. We find that the central dwarf galaxies in the group are redder and brighter than the outer dwarfs. The faint-end slope, a=-1.33, of the luminosity function of the NGC 2784 group is consistent with results for other groups, but steeper than that of the Local Group. The KMTNet survey will provide homogeneous catalogs of dwarf galaxies in 15–20 groups.

Star Clusters and Young Populations in the Leo A Galaxy

Stonkute, Rima

We have studied young stellar populations and star clusters in the dwarf irregular galaxy Leo A using multicolour photometry data obtained with the Subaru Telescope and HST ACS. Analysis of the main sequence and “blue loop” stars allowed us to determine the star formation history in the Leo A galaxy during the last 500 Myr. Also, we have discovered numerous star clusters in the main body of the Leo A galaxy. The colour-magnitude diagrams and integrated photometry data of the newly discovered star clusters were used to study cluster population in the Leo A galaxy.

Gas Temperature Demography in the Magellanic Clouds

Liu, Boyang

A galaxy's star formation rate is partially determined by how quickly gas converts from diffuse atomic (HI) state to molecular (H2). This HI-H2 conversion is affected by the amount of metal in the gas and the strength of interstellar radiation fields. We have conducted an Australia Telescope Compact Array (ATCA) observation project that uses HI absorption to probe the HI-H2 conversion within disparate environments in two local laboratories: the nearby Large and Small Magellanic Clouds. This project will complement the ASKAP survey, GASKAP and help us understand the gas processes that lead to star formation and how these impact galaxy evolution throughout the Universe. Our project observed 48 sightlines in LMC and 31 in SMC with 6km configuration of ATCA telescope, which doubled the total number of sampling. By Jan 2018 we have completed all the ~850 hours observation and derived the preliminary results for the temperature distribution of atomic gas in the Magellanic Clouds. We'll show the results and its implications for our knowledge of ISM evolution and galaxy formation.

MoRIA dwarf galaxies in the Fornax cluster environment

Mastropietro, Michele

We investigate the evolution of dwarf galaxies falling into the Fornax cluster starting from a selection of the MoRIA (Models of Realistic dwarfs In Action, Verbeke et al. 2015, 2017) suite of simulations.We first simulate the dwarfs outside the cluster up to 8 Gyr in order to obtain realistic late-type dwarf galaxies to inject into the cluster. Our simulations include detailed subgrid physics processes (radiative cooling, supernova feedback, UV background effects, and ionization-aware internal energy and equation of state of the gas) coded in a heavily modified GADGET-2 version developed in our group.We model the Fornax cluster gravitational potential as an NFW density profile and the intracluster gas density distribution as a beta model following Paolillo et al. (2002). We have carried out a set of simulations starting from a range of different trajectories and we study first separately and then together the effects of tidal stirring and ram-pressure stripping trying to isolate their effects. We show the results of the simulations following the dwarfs' journey into the Fornax cluster environment by tracking their star formation rates, gas distribution, stellar dynamics, and metallicity distribution.

Refueled and shielded - the early evolution of Tidal Dwarf Galaxies

Baumschlager, Bernhard

We present, for the first time, numerical high-resolution simulations of young tidal dwarf galaxies (TDGs), including a self-consistent treatment of the tidal arm in which they are embedded. Thereby, we do not rely on idealised initial conditions, as the initial data of the presented simulation stem from a galaxy interaction simulation. We compare these embedded models with those ones ususally applied but isolated from the tidal arm. Here we demonstrate the importance of the tidal-arm gas reservoir on the evolution of TDGs as gas can be accreted and is available for subsequent conversion into stars. During the initial collapse of the initially Jeans unstable proto-TDG, with a duration of a few 100 Myr, the evolutions of the embedded and isolated TDGs are indistinguishable. Significant differences appear however after the collapse has halted and the further evolution is dominated by the ongoing accretion of material from the surroundings of the TDGs. The inclusion of the tidal arm in the simulation of TDGs results in roughly a doubling of the gas mass and gas fraction, an increase in stellar mass by a factor of 1.5 and a ~5 times higher star formation rate (SFR) compared to the isolated case.Such high SFR leads to compact young blue star-dominated dwarf galaxies (DGs) which will survive supernova feedback and lateron either dissolve from the mature galaxy as ilolated dwarf ellipticals or when keep bound probably develop to the type of faint compact DGs found as satellites around massive cluster galaxies.

Dynamical models of dwarf spheroidals in the Gaia era

Posti, Lorenzo

The Gaia mission is revolutionizing our knowledge of the Local Group by allowingthe 3D motions of individual stars to be measured even in the brightest dwarfSpheroidals (dSphs). These measurements are of vital importance for dynamical studiesof dSphs since they completely break the mass-velocity anisotropy degeneracy andthus they allow for a uniquely robust inference on how dark matter is distributed.As data quality is making a huge leap forward, dynamical models must keep up thispace to stand up for the challenge of finally pinning down the dark matterdistribution in the systems that currently pose the biggest threat to standardcosmological models.I will show how our pioneering measurement of the proper motion of stars in theSculptor dSph (obtained combining Hubble+Gaia, Massari et al. 2018) can be usedto constrain how dark matter is distributed in the galaxy. Novel multi-componentdynamical models generated with analytic distribution functions (that we introducedin Pascale et al. 2018) are crucial to this end: we demonstrate how the inferenceon the galaxy's physical properties changes when using our new Bayesian approach,maximizing the natural likelihood that is the distribution function, as opposed toa more classical approach, of merely fitting to the radially binned starcount/line-of-sight velocity profiles. The likelihood of the model strongly dependson the proper motions for stars that have them measured, while it is marginalizedover the tangential velocity for those that do not have proper motions.The distribution function models that we use not only account for the multiplestellar populations revealed in Sculptor, but they also well characterize theirdifferent kinematics, hence offering important constraints on dwarf galaxy formationmodels.

Red Supergiants as Chemical abundance Probes: The Local Group dwarf NGC6822

Patrick, Lee

Red Supergiant Stars (RSGs) are important probes of stellar and chemical evolution in star-forming environments. They represent the brightest near-IR stellar components of external galaxies and probe the most recent stellar population to provide robust, independent abundance estimates. The Local Group dwarf irregular galaxy, NGC6822, is a reasonably isolated galaxy with an interesting structure and turbulent history. Using RSGs as chemical abundance probes, we estimate metallicities in the central region of NGC6822, finding a suggestion of a metallicity gradient (in broad agreement with nebular tracers), however, this requires further study for confirmation. With intermediate resolution Multi-object spectroscopy (from e.g. KMOS, EMIR, MOSFIRE) combined with state-of-the-art stellar model atmospheres, we demonstrate how RSGs can be used to estimate stellar abundances in external galaxies and present an overview of recent efforts to estimate the Mass-Metallicity relation of galaxies, a key diagnostic of the chemical evolution of galaxies, using stellar tracers alone. In this context, we compare stellar and nebular abundance tracers and highlight the potential of this technique with the upcoming/current generation of ground- and space-based telescopes.

A Top-Light IMF in Low Surface Brightness Environments

Meurer, Gerhardt

We use direct imaging with the Hubble Space Telescope to construct the main-sequence luminosity function of five nearby dwarf galaxies and spiral galaxy outskirts. The luminosity functions are consistent with the paucity of O stars relative to B stars inferred from Halpha and ultraviolet imaging observations.  Hence, the observations disfavour the interpretation of low Halpha/FUV ratios as being due to escaping ionizing photons and instead favour an Initial Mass Function deficient in high mass stars compared to the canonical Salpeter IMF.

The local properties of supernovae explosion and their host galaxies

Liang, Yanchun

To understand the local properties of supernova explosion, and to compare those with the global properties of the host galaxies, we analyze the integral field spectragraph (IFS) of Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) for a sample of 11 SNe host galaxies selected from MaNGA-MPL4 and Asiago supernova catalogue. We obtained the 2D maps and gradients of the Ha velocity field , oxygen abundace , surface stellar mass density, specific star formation rate and star formation rate density, mean stellar population age etc. for the sample galaxies. These properties are analyzed for the individual object.  We also try to obtain a general idea for the sample. For example, the differences between local and global gas-phase oxygen abundance of SNe Ia hosts cover a wider range than that of SNe II hosts. An extended sample up to 50 from MPL6 is under analyzed to get more statistical properties.

OGLE-ing the Magellanic System: Three-Dimensional Structure

Jacyszyn-Dobrzeniecka, Anna

I will present a three-dimensional structure of the Magellanic System using over 9000 Classical Cepheids (CCs) and almost 23000 RR Lyrae (RRL) stars from the OGLE Collection of Variable Stars. Given the vast coverage of the OGLE-IV data and very high completeness of the sample we were able to study the Magellanic System in great details.Lately, we have very carefully studied once again the distribution of both types of pulsators in the Magellanic Bridge area. We showed that there is no evidence of an actual physical connection between the Clouds in RRL stars distribution. We only see the two halos overlapping. There are few CCs in the Magellanic Bridge area that seem to form a genuine connection between the Clouds. Their on-sky locations are very well correlated with young stars and neutral hydrogen distribution.CCs in the LMC are situated mainly in the bar that shows no offset from the galaxy plane. The norther arm is also very prominent. Moreover, it is located closer to us than the entire sample. The CCs in the SMC have a non-planar distribution that can be described as an ellipsoid extended almost along the line of sight. RRL stars revealed a very regular distribution in both Magellanic Clouds. We fitted triaxial ellipsoids to our LMC and SMC RRL samples.

??Mean field dynamo in dwarf galaxies

Bera, Prasanta

Dwarf galaxies are generally faint but these are highly abundant in number count. Some of these galaxies (e.g. NGC 1569, IC 10, NGC 4449) show a strong large-scale magnetic field of strength about 10µG or more. The presence of an ordered strong magnetic field with similar strength in spiral galaxies is considered to be generated from the seed magnetic field by the dynamo action due to the differential rotation in the disk plane. On the other way, the strength of the differential rotation is small in a dwarf galaxy hence does not usually prefer large-scale dynamo. From the study of mean field dynamo in a thick disk, we find that the resistive dissipation is effectively less due to thicker vertical height. It can generally explain the strong ordered magnetic field in the dwarf galaxies.

What are the implications of stellar chemical abundances in dwarf galaxies?

Suda, Takuma

Chemical abundances of stars provide us with rich information on the star formation history and the chemical evolution of the universe. Thanks to the many efforts to derive the abundances of individual stars in dwarf galaxies, it is possible not only to compare them with those in the Milky Way but to compare among dwarf galaxies in the local group. We have constructed a database of stellar abundances in the local group dwarf galaxies by extending the existing database for Milky Way stars (The Stellar Abundances for Galactic Archaeology database,, see Suda et al. 2008, PASJ, 60, 1159). We analyzed the data in the new database, which contain more than 6000 stars in 24 dwarf galaxies together with more than 4500 stars in the Milky Way. The large dataset of stellar abundances enables us to explore the characteristics of dwarf galaxies with various approaches. In this presentation, we elaborate our analyses on the chemical abundances of stars in the local group dwarf galaxies and discuss the constraints on their origins. Our statistical approach provides a hint to inspect the star formation history of individual galaxies, using cumulative metallicity distribution functions. In addition, the compilation of all the available data on the abundances of carbon and neutron-capture elements has revealed the variations of the population of carbon-enhanced metal-poor stars, which gives an important insight into our understandings of the chemical enrichment history of galaxies. The inspection of the relationship between Eu and Ba abundances confirms an anomalously Ba-rich population in Fornax, which indicates a pre-enrichment of interstellar gas with r-process elements. We also checked the anti-correlations in O–Na and Mg–Al abundances to see a similarity with the Galactic globular clusters, which results in no evidence of the abundance anti-correlations in any dwarf galaxies. (Reference: Suda et al. 2017, PASJ, 69, 76)

Study of galaxies in the Eridanus void.

Egorova, Evgeniya

We present a sample of 66 galaxies belonging to the equatorial part (Dec.= –7?, +7?) of the large so called Eridanus void. Our main goal was to study systematically the evolutionary parameters of the void sample (metallicity and gas content) and to compare the void galaxy properties with their counterparts residing in denser environments. Besides the general galaxy parameters, compiled mainly from the literature, we present the results of the dedicated observations to measure the oxygen abundance O/H in HII-regions of void galaxies with the 11-m SALT telescope (SAAO) and the 6-m telescope BTA (SAO), as well as the O/H estimates derived from the analysis of the SDSS DR7 spectra. We use this O/H data to build for our sample the relation log(O/H) versus MB, which we compare  with that of the ‘reference’ sample of similar type galaxies from the Local Volume. We find a clear evidence for the substantially lower average metallicity of the Eridanus void galaxies. This result well matches the conclusions of our recent similar study for galaxies in the Lynx-Cancer void.

The major merger origin of the Andromeda II kinematics

Ebrova, Ivana

Prolate rotation (i.e. rotation around the long axis) has been reported for two Local-Group dwarf galaxies: Andromeda II, a dwarf spheroidal satellite of M31, and Phoenix, a transition type dwarf galaxy. The prolate rotation may be an exceptional indicator of a past major merger between dwarf galaxies. We showed that this type of rotation cannot be obtained in the tidal stirring scenario, in which the satellite is transformed from disky to spheroidal by tidal forces of the host galaxy. However, we successfully reproduced the observed Andromeda II in controlled, self-consistent simulations of mergers between equal-mass disky dwarf galaxies on radial or close-to-radial orbit. In simulations including gas dynamics, star formation and ram pressure stripping, we are able to reproduce more of the observed properties of Andromeda II: the unusual rotation, the bimodal star formation history and the spatial distribution of the two stellar populations, as well as the lack of gas. We support this scenario by demonstrating the merger origin of prolate rotation in the cosmological context for sufficiently resolved galaxies in the Illustris large-scale cosmological hydrodynamical simulation.

Census of Lya, [OIII]5007, Ha, and [CII]158um Line Emission with ~1000 Low-mass Lyman Alpha Emitters at z=4.9-7.0 Revealed with Subaru/Hyper-Suprime Cam Survey

Harikane, Yuichi

We investigate Lya, [OIII]5007, Ha, and [CII]158um emission from 1,125 low-mass galaxies (typically M*~10^8 Mo) at z=4.9-7.0, composed of 1,098 Lya emitters (LAEs) at z=4.9-7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys and 29 galaxies at z=5.148-7.508 with deep ALMA [CII]158um data in the literature. Fluxes of strong rest-frame optical emission lines ([OIII] and Ha) are constrained by significant excesses found in the Spitzer 3.6 and 4.5um photometry. At z=4.9, we find that the rest-frame Ha equivalent width and the Lya escape fraction positively correlate with the rest-frame Lya equivalent width, EW^0_Lya. The typical ionizing photon production efficiency of LAEs is logxi_ion/[Hz erg^-1]~25.5, significantly (60-100%) higher than those of LBGs at a given UV magnitude, indicating the significant role of these low-mass galaxies in the cosmic reionization. At z=5.7-7.0, there exists an interesting turn-over trend that the [OIII]/Ha flux ratio increases in EW^0_Lya~0-30 A, and then decreases out to EW^0_Lya~130 A. We also identify a ~3sigma negative correlation between a [CII] luminosity to star-formation rate ratio (L_[CII]/SFR) and EW^0_Lya. We carefully investigate physical origins of these relations with stellar-synthesis and photoionization models, and find that a simple anti-correlation between EW^0_Lya and metallicity explains self-consistently all of the relations of Lya, Ha, [OIII]/Ha, and [CII] identified in our study, indicative of the detections of the very metal-poor (~0.04 Zo) low-mass galaxies with EW^0_Lya~200 A.

Dwarf galaxies and their globular cluster systems: data analysis and non-stationary formation model

Nuritdinov, Salakhutdin

Because of the deficiency problem of dwarf galaxies (DG) in the Universe relatively to quantity of usual Hubble galaxies the research of those which contain the globular cluster systems (GCS) is of interest.    We have collected the data of observations for 76 DG containing the GCS. About 95% of them are elliptical DG. We have received that the absolute magnitude of DG depends linearly on values of both the metallicity and logarithm of quantity of globular clusters around them. A dependence of the ellipticity degree of DG on average quantity of globular clusters is studied. An empirical dependence of masses of DG on quantity of globular clusters around them is also found. We have offered a non-stationary model of the collapsing protogalaxy against a background of which both the poor GCS and the dwarf galaxy can be formed.

The dynamics of the ionized gas associated with the SMC Cluster NGC 346

Smith, Linda

The young resolved cluster NGC 346 in the SMC provides us with the opportunity to study the details of cluster formation and the efficiency of feedback mechanisms at low metallicity. We present high resolution (7 km/s) spectroscopy of the ionized gas, and find that the gas is largely quiescent over the extent of the ionized region N66. We find that some of the young sub-clusters are associated with broad emission-line components and discuss their origin. Overall, we find that the winds of the cluster O stars are not sufficient to clear N66 of gas and that stellar radiation is the dominant process shaping the interstellar environment of NGC 346. 

Understanding the evolution of dwarf galaxies in the Fornax cluster using the Fornax Deep Survey data

Venhola, Aku

A variety of environmental and internal processes affect the evolution of dwarf galaxies. To understand the importance of these processes, we need to statistically analyze compete galaxy samples with homogeneous data and measurements. The Fornax Deep Survey (FDS) is a new survey providing ultradeep u'g'r'i'-data covering 26 deg2 area in the Fornax cluster and the Fornax A group. The data allows high resolution analysis of dwarf galaxies down to absolute r-band magnitude Mr ~ -10 mag. Using the FDS-data, we have generated the most extensive magnitude and size limited catalog of dwarf galaxies in the Fornax cluster including more than 600 cluster dwarfs. We fit the light distributions of these dwarf galaxies with Sersic-profiles using GALFIT to obtain their structural parameters, and measure aperture colors. We also classify the dwarf galaxies into late- and early-types according to their morphology and study them separately. We then analyze the projected distribution, luminosity function, structure and colors of the dwarf galaxies in the cluster, and study how these properties change in different cluster-centric bins. Finally, we discuss how our results can be interpreted with the current understanding of environmental processes taking place in galaxy clusters.?

The Too-Big-To-Fail problem in the field - Insights from realistic dwarf simulations

Verbeke, Robbert

We test whether advanced galaxy models and analysis techniques of simulations can alleviate the Too-Big-To-Fail problem(TBTF) for late-type galaxies(Papstergis et al. 2015), which states that isolated dwarf galaxy kinematics imply that dwarfs live in lower-mass halos than is expected in a ?CDM universe. Furthermore, we want to explain this apparent tension between theory and observations.Previously, we have used the MoRIA (Models of Realistic dwarfs In Action) suite of dwarf galaxy simulations (Verbeke et al. 2015) to investigate whether observational effects are involved in TBTF for late-type field dwarf galaxies. To this end, we created synthetic radio data cubes of the simulated MoRIA galaxies and analyse their HI kinematics as if they were real, observed galaxies.We found that for low-mass galaxies, the circular velocity profile inferred from the HI kinematics often under-estimates the true circular velocity profile, as derived directly from the enclosed mass. Fitting the HI kinematics of MoRIA dwarfs with a theoretical halo profile results in a systematic underestimation of the total mass of their host halos. We attribute this effect to the fact that the interstellar medium of a low-mass late-type dwarf is continuously stirred by supernova explosions into a vertically puffed-up, turbulent state to the extent that the rotation velocity of the gas is simply no longer a good tracer of the underlying gravitational force field. If this holds true for real dwarf galaxies as well, it implies that they inhabit more massive dark matter halos than would be inferred from their kinematics, solving TBTF for late-type field dwarf galaxies (Verbeke et al. 2017)In this talk, I will present results from a suite of new, even more realistic dwarf galaxy simulations and discuss the Too-Big-Too-Fail problem in the field and potentially other cosmological questions.

The prevalence and properties of ultra-diffuse galaxies in local clusters

Skelton, Rosalind

Ultra-diffuse galaxies (UDGs) are an unusual class of low surface brightness galaxies that have recently come into the spotlight for their low stellar masses (similar to those of dwarf galaxies) but large sizes and total masses much closer to those expected in a more massive galaxy, such as the Milky Way. How they form and remain intact within the strong tidal fields of the clusters they are typically found in remains unknown, but their locations and properties in relation to their larger-scale halos may provide clues. We present our results on the distribution of UDGs found in clusters in the relatively deep Stripe 82 region of the Sloan Digital Sky Survey. The clusters are selected from the redMaPPer catalogue out to z~0.2. A comparison of these diffuse low-mass galaxies with more typical dwarf galaxies in clusters may shed light on the processes affecting their evolution.

Dwarf Galaxies in the core of Coma Cluster

Hasan, Syed

 Dwarf galaxies constitute 24% of the galaxies in the core of the Coma Cluster. In this talk,  I present the correlation between structural properties and morphology of galaxies in the central region of Coma Cluster for 221 objects within the apparent magnitude range m < 19.5. The data is taken from the HST/ACS Coma Cluster Treasury Survey and Source Extractor Catalogue compiled by Hammer et. al. 2010. For cluster membership we have used photometric redshifts of Michard et. al. 2008 & Edwards et. al.,2002 and spectroscopic redshifts of SDSS DR9 catalog. From the investigation of correlations of effective radius, Sersic index, absolute magnitude and bulge to total light ratio, we find that giants constitute 73%, Dwarf galaxies constitute 24% and the remaining 3% are Spirals+Irr+Ring. We found that multiple component fits are best for giants and the single Sersic fit is best for Dwarfs & Spiral galaxies. We shall try to explain why the single Sersic fit is best for Dwarfs and what kind of stellar orbits do they correspond to. 

A spatially resolved view of molecular clouds at reduced metallicity in the Magellanic Clouds

Zahorecz, Sarolta

The Magellanic Clouds offer the opportunity to obtain a spatially resolved view of external galaxies at reduced metallicity with no distance ambiguity. Especially, the SMC represents a unique astrophysical laboratory because of its proximity, lower ISM metallicity, and tidally disrupted interaction status. The SMC offers a rare glimpse into the physical processes in an environment with a metallicity that is below the threshold of 1/4–1/3 Zo, where the properties of the ISM in galaxies change significantly. We have performed ALMA observations in various molecular lines toward the active star-forming region N83C in the SMC. The observations first revealed subparsec-scale molecular structures in 12CO and 13CO (2-1) emissions (Muraoka et al. 2017). We found strong CO peaks associated with YSOs and derived a typical gas density of ~104 cm-3 and gas temperature of 40-60 K from the excitation analysis. The high gas density and temperature are presumably due to the effect of the HII region under the low-metallicity environment in the SMC; far-UV radiation can easily penetrate and photodissociate the outer layer of 12CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in 12CO emission. This molecular gas distribution is compared with that in the LMC and the Galaxy, where the filamentary structure is dominated, with the same actual spatial resolution; ALMA for the LMC, and large/small single dish telescopes for the Galaxy. We have recently carried out ALMA observations toward N83C in [CI] (1-0) to investigate the photodissociation of CO in the low metallicity environment. The column density ratios N(CI)/N(CO) are generally high throughout the cloud compared with the Galaxy, ranging from 0.2 to 2.0. A peak of the ratio is observed toward a CO peak associated with a massive protostar; the enhancement of the ratio toward the dense gas is rarely seen in molecular clouds in the Galaxy. 

An Upper Mass Limit for a Black Hole in the Large Magellanic Cloud

Luetzgendorf, Nora

As one of our closest galactic neighbours, the center of the Large Magellanic Cloud (LMC) is an enticing place to look for a central black hole (BH). Due to the large size of the LMC on the sky and the complexity of its dynamics, the center of this dwarf galaxy is still only known to ~ 30 arcmin. Here we present a new study of the stellar kinematics near the center of the LMC, and use this to provide the first constraints on the possible presence of a central black hole. With the impressive field of view of the Multi Unit Spectroscopic Explorer (MUSE) for the Very Large Telescope this is the largest region of the LMC mapped with integrated light. We identify and subtract the galactic foreground population and use the Calcium Triplet (~ 850nm) spectral lines to create a 2D radial velocity map with an unprecedented spatial resolution of 1 arcmin2. Comparison of this map with kinematic models yields 3s upper-mass-limit of 107.1 M? for any black hole within the center of the LMC. Considering the poorly constrained scaling relations between BH masses and their host galaxies on the lower-mass end, the study of such a nearby dwarf galaxy and its potential black hole can shed light on many theories of BH formation, growth, and host system interaction. It is also still unknown what fraction of low-mass galaxies contain black holes, and the measurements remain difficult to achieve. This study is a promising step in searching for the kinematic signature of black holes in the elusive intermediate mass range and contributes to the growing understanding of the complex dynamics of the LMC’s central bar region.

The star formation relation in atomic hydrogen dominated dwarf galaxies

Roychowdhury, Sambit

Star forming dwarf irregular (dIrr) galaxies are the most numerous galaxies in the nearby Universe, closely resembling the first galaxies that formed. They represent a goldmine in our own backyard for studying the baryon cycle in the smallest galaxies. Recent large multi-wavelength surveys of the Local Volume has made it possible to study these galaxies in considerable detail.Atomic hydrogen (HI) remains the primary tracer of gas in these systems as CO, the tracer of molecular gas, become harder to detect due to a decrease in the CO-to-H2 ratio with decreasing metallicity. The atomic gas traces the total gas reservoir in dwarf irregulars - and consequently the whole ecosystem within which stars form.I will start with recent results from my studies using the Faint Irregular Galaxy GMRT Survey (FIGGS). I show that when one measures the star formation rates (SFRs) correctly after accounting for the stochasticity, one finds the same 'Kennicutt-Schmidt relation' between surface densities of gas and SFR within resolved sub-kpc sized regions - in both dIrrs and outskirts of spirals, and a more efficient one than previously believed. More importantly, the relation is consistent with models of star formation which take the effects of stellar and supernova feedback into account.The importance of feedback from earlier generations of stars is reiterated in my study where I extend the range of validity of the 'extended Schmidt law' to the lowest metallicity galaxies, by showing that dIrrs also follow the law.Finally I will present my recent efforts to model the full baryon cycle in the lowest (<20% solar) metallciity star forming dwarfs from the well-defined DustPedia sample, which has multi-wavelength coverage in 42 bands ranging from the ultraviolet to submillimeter. Adding resolved HI maps, and using SFR and dust properties derived from SED fits using a hierarchical Bayesian approach, I create a model of the gas-stars-dust cycle using the latest chemical evolution models.

Outlying H-alpha blobs in SDSS IV MaNGA

Bait, Omkar

We have discovered a population of 28 outlying H-alpha emitters which appear as unresolved blobs in the SDSS IV MaNGA integral field unit (IFU) survey. These could be candidate dwarf galaxies with high specific star formation rates (sSFRs). We have used the recently released stellar population and ionized gas emission maps, derived using the Pipe3D pipeline, to visually identify H alpha emitting regions with no underlying optical continuum emission in deep imaging from the DECam Legacy Survey or Beijing-Arizona Sky Survey. Moreover, these H-alpha blobs have velocities which are different from the velocity map of the host galaxies. Starting from a sample of $\sim 2700$ MaNGA galaxies in the  Data Release 14, we identify 28 outlying H-alpha emitting blobs. We make apertures around these blobs and calculate the total fluxes around various emission lines to study their location on the Baldwin Philip and Terlevich (BPT) diagram, which shows that all of them are photoionised due to star formation. We also estimate their total star formation rates (SFR) and metallicities using the integrated emission lines.  We use the non-detections in the optical continuum as an upper limit on the absolute magnitude in the B band ($M_B$) of these candidate dwarf galaxies and compare them with the well known $M_B$-SFR and $M_B$-metallicity relations. We found that these galaxies have very high sSFRs compared to the local volume dwarfs. Some of the dwarf galaxies could belong to the faint end of the blue compact dwarfs (BCDs), blue diffuse dwarfs (BDDs), or tidal dwarf galaxy (TDGs) populations. However, the metallicites of these dwarfs galaxies shows that they are either consistent with or have lower metallicities than the standard $M_B-metallicity$ relation. Hence, we can at least rule out the possibility of them being TDGs.

The role of environment on the star formation history of disc galaxies

Chang, Ruixiang

NGC 2403, NGC 300 and M33 are three nearby pure-disc galaxies with similar stellar mass in different environments; they are benchmarks for understanding late-type spiral galaxies in different environments. The chemical evolution and growth of their discs are investigated by using the simple chemical evolution model, in which their discs are assumed to originate and grow through the accretion of the primordial gas, and the gas outflow process is also taken into account. Through a comparative study of the best-fitting model-predicted star formation histories for them, we hope to derive a picture of the local environment on the evolution and star formation histories of galaxies and whether or not the isolated galaxies follow similar evolution history. Our results show that these three galaxies accumulated more than 50 per cent of their stellar mass at z < 1. It can also be found that the metallicity gradients in isolated spiral galaxies NGC 2403 and NGC 300 are similar and obviously steeper than that in M33, when the metallicity gradients are expressed in dex R_25^{-1}. The similar metallicity gradients in NGC 2403 and NGC 300 indicate that they may experience similar chemical evolutionary histories. The principal epoch of star formation on the discs of NGC 2403 and NGC 300 is earlier than that on the disc of M33, and the mean age of stellar populations along the discs of both NGC 2403 and NGC 300 is larger than that of M33. Our results indicate that the evolution and star formation history of a galaxy indeed depend on its local environment, at least for galaxies with stellar mass of 10^{9.2}-10^{9.7} M_{?}.

Chemical evolution model to derive metallicity distributions for each stellar population

Homma, Hidetomo

I have constructed a new chemical evolution model for dwarf galaxies and compares its results with the observed chemical properties of red giant branch stars (RGBs) and RR Lyrae (RRL) stars of Sculptor and Fornax dwarf spheroidal galaxies (dSphs). The detailed chemical abundances of RGBs of nearby dwarf galaxies have been measured by spectroscopic observations. Moreover, the metallicity distributions of RRL stars are estimated from the theoretical Period-Luminosity relations in literature and it is found that the mean metallicity of RRL stars are lower than that of RGBs. In order to investigate the metallicity distributions of RGBs and RRL stars, the chemical evolution model of this study adopts the Padova stellar evolution tracks and derives the metallicity distributions of RGBs and RRL stars, respectively. Moreover, in order to derive the consistent chemical evolution with the observed color magnitude diagrams, the model adopts the star formation histories estimated from the color magnitude diagrams. The resultant chemical evolution models represent the observed metallicity distributions of RGBs in Sculptor and Fornax dSphs, respectively. However, the mean metallicity of RRL stars of the model of Sculptor dSph is lower than that of the previous work. Since the metallicity of RRL stars estimated from the theoretical Period-Luminosity relations depends on the distance modulus, it is found that the distance modulus of Sculptor dSph are larger than that of the previous work in order to represent the metallicity distributions of RGBs and RRL stars, simultaneously. The distance modulus of Sculptor and Fornax dSph derived from the chemical evolution models are $19.67 ¥pm 0.08$ and $20.81 ¥pm 0.13$, respectively. These values are consistent with the other previous works.

Science with the Fornax Deep Survey - a new complete census of 600 dwarf galaxies

Peletier, Reynier

28 years after Ferguson’s FCC, we have produced a new galaxy survey of the Fornax Cluster, covering a region of 26 square degrees. The survey in u’g’r’i’ is based on OmegaCAM images at the VST, at a depth comparable to the NGVS survey. Authors of this survey, the Fornax Deep Survey, based on GTO observations, are a an NL-led team (PI Peletier) and an Italian-led team (PI Iodice), of in total about 40 scientists. Our survey is being suppplemented by a variety of anciliary observations, including a K-band imaging survey,  IFU observations of 50 dwarf galaxies and CO-observations taken with ALMA. HI observations are planned using the MeerKAT telescope.The scientific goals of the FDS project are diverse. We aim to study in detail the baryonic substructures, ranging from massive galaxies to small spheroidal galaxies and star clusters. The data have considerable legacy value, and will serve as a local reference for high redshift studies. The survey is ideal to study the influence of the galaxy environment on stellar populations. In particular, this allows us to study dwarf galaxies in unprecedented detail.In this presentation I will discuss the most important science results obtained up to now in the regime of dwarf galaxies, including:- A comprehensive magnitude and size-limited catalog of ~600 dwarf galaxies has been produced, of which colors and structural parameters have been obtained, leading to new insights in the formation and evolution of dwarf galaxies. These are discussed in the presentation of Aku Venhola.- A survey of Ultra Diffuse and other LSB galaxies in Fornax, clearly indicating a deficit of UDG/LSB galaxies in the center of the cluster (Venhola et al. 2017)- High spectral resolution SAMI IFU data for 50 galaxies, in an effort to obtain detailed spatially resolved kinematics and stellar populations for a complete sample of dwarfs, going fainter than anything currently available in the literature.

Unravelling M31's accretion history

DSouza, Richard

M31, our nearest large galactic neighbour, offers a unique opportunity to test how mergers of dwarf galaxies affect galaxy properties. M31's stellar halo caused by the tidal disruption of dwarf satellite galaxies is the best tracer of the galaxy's accretion history. Here we use cosmological models of galaxy formation to show that M31’s massive and metal-rich stellar halo containing intermediate age stars implies that it merged with a large (M* ~ 2.5 x 10^10 M_sun) galaxy ~2 Gyr ago. The simulated properties of the merger debris help to interpret a broader set of observations of M31’s stellar halo and satellites than previously considered: its compact and metal-rich satellite M32 is the tidally-stripped core of the disrupted galaxy, M31’s rotating and flattened inner stellar halo contains most of the merger debris, and the giant stellar stream is likely to have been thrown out during the merger. This merger may explain the global burst of star formation ~2 Gyr ago in the disk of M31 in which ~1/5 of its stars were formed. Moreover, M31’s disk and bulge were already in place before its most important merger, suggesting that mergers of this magnitude do not dramatically affect galaxy structure. This merger may also hypothetically explain the corotating plane of satellites of M31.

Superbubbles and triggering of star formation in nearby dwarf irregular galaxies

Egorov, Oleg

Dwarf irregular (dIrr) galaxies provide the best environment for studying the influence of supernovae and stellar winds onto the ISM leading to creation of the superbubbles and large HI supershells. Thanks to thick solid-body rotating discs, such structures grow to a large sizes (up to several kpc) and live longer than in spiral galaxies. The interaction of the HI supershells might trigger a new burst of star formation in a galaxy, while the influence of ongoing star formation in their rims might lead to dissolution of the HI structures. Here we present the results of long-term observations of several nearby dIrr galaxies made with a scanning Fabry-Perot interferometer and narrow-band filters performed at the 6-m telescope of SAO RAS. An analysis of the ionized gas morphology and kinematics in star forming regions of these galaxies allowed us to identify a number of expanding superbubbles, as well as a lot of filament-like ionized structures. We show that star formation in the observed galaxies mainly take place in the unified complexes with sizes of several hundreds pc inside the rims of giant HI supershells. A certain signs of star formation propagation within these complexes, as well as its triggering at the scales of the whole complexes, are detected.

Boosting the Lya line in Pop III Galaxies from Stochastic IMF Sampling

Forero-Romero, Jaime

The sensitivity of the Lya flux to the high-energy end of the galaxy spectrum makes it subject to stochastic sampling of the IMF. Stochasticity introduces a dispersion in the predicted nebular line fluxes around the deterministic value by as much as a factor of ~4.  Stochastic sampling also affects the expected Equivalent Width making it possible to have an EW as high as ~3 times the deterministic value. Stochastic models seem to be required for a proper interpretation of future distant galaxy detections to be made with facilities such as JWST and other large, groundbased telescopes.

Investigating Multiple Stellar Populations and Rotation in intermediate-age LMC star clusters

Asad, Randa

The extended main sequance turn off (eMSTO) has been observed in many intermediate-age star clusters. It's origin is still debatable, it could be due to multiple stellar popuations (MSP) or stelar rotation or other factors.  We use a new approach to investigate the MSP scenario, as well as rotation in star clustes by means of integrated spectra. Our results are consistent with the results obtained from CMD studies. Our presentation will give details on each of the clusters studies and compare it with the CMD literature result. 

The nature of the Triangulum-Andromeda stellar structures

Sales Silva, João

The Milky Way was formed in a complex chain of physical processes involving dissipative gravitational collapse, gas flows, and galactic mergers. The outer stellar halo is home to a number of substructures that are remnants of former interactions of the Galaxy with its dwarf satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as a debris cloud by Rocha-Pinto, et al. (2004, ApJ, 615, 732) using 2MASS M giants. Recently, using SDSS data, Perottoni et al. (2018, MNRAS, 473, 1461) have uncovered several scattered dense excesses of main sequence stars situated in the TriAnd region. At least two of these excesses may represent new, not previously known, stellar structures, and one of them resembles a stellar stream. A similar discovery was made by Martin, et al. (2014, ApJ, 787, 19) in a smaller area around M 31. The better photometry in Martin, et al. (2014, ApJ, 787, 19) data points to a likely mix of stellar populations in these debris. I will present a study abundance patterns using high resolution spectroscopy of giant candidate stars that are situated in the overdensity regions of the stellar maps by Martin et al. (2014, ApJ, 787, 19) and Perottoni et al. (2018, MNRAS, 473, 1461), which may gives us clues on whether these stars may have been tidally stripped from a former dwarf satellite.

A Population of Gas-Poor Field Dwarfs in the Local Volume?

Karunakaran, Ananthan

We have searched for atomic gas along the lines-of-sight to low surface brightness (LSB) features that project near Local Volume galaxies in order to explore the possibility that they are dwarf satellites of the latter. The properties of the satellite populations of galaxies are vital for understanding galaxy formation and evolution. Wide-field optical imaging campaigns are effective at detecting LSB features, however, typical optical follow-up methods are expensive; the distances to these putative dwarf galaxies, and therefore their association with their putative parents, are unknown. We exploit well-known atomic gas (HI) properties of low-mass systems to constrain this association. Dwarf galaxies in the field are almost ubiquitously gas-rich while low mass satellites within the virial radius of a massive host are gas-poor; an HI non-detection along the line of sight to an LSB feature supports the hypothesis that it is a dwarf satellite of its putative parent. We have performed GBT observations to search for HI reservoirs in 48 LSB features detected in deep images near known Local Volume galaxies. While we do find some gas-rich dwarfs around nearby massive hosts and in the field, the vast majority (~80%) of our observations yield stringent non-detections. Surprisingly, a number of them correspond to LSB features that are not resolved into stars by HST, placing a firm lower limit on their distances and rule out the possibility that they are satellites of their nearest Local Volume host. Combining GBT and HST results, we find that these systems are plausibly gas-poor, M* ~10^7 Mo field dwarfs. We will report on our efforts to distinguish real satellite galaxies from background interlopers around nearby galaxies, compare their measured properties to established dwarf galaxy scaling relations, and explain how the predictions of these relations can be reconciled with our observations by invoking a population of gas-poor, field dwarfs in the Local Volume.

Chemical evolution models for Leo A and IC1613.

Hernández-Martínez, Liliana

We have developed one-zone chemical evolution models (CEM) for two dIrr galaxies, analysing their chemical evolution in a cosmological context. One of our main constraints in our chemical evolution models is the star formation rate obtained from very deep observations.  As part of our results, we are able to reproduce the metallic evolution estimated by observations. We have two main results: 1) from our CEM we can infer the mass assembly history (MAH) of each dIrr galaxy, and 2) we propose to include an outflow mainly driven by star formation, in order to reproduce the metallic evolution for Leo A while for IC 1613 the required outflow model must be more complex and ir would be explain in detail.

Uncovering how Lyman alpha photons escape by studying dwarf galaxies in the near-by universe.

Melinder, Jens

The Lyman alpha reference sample (LARS) is a major multiwavelength imaging andspectroscopic campaign of star-forming dwarf galaxies, as well slightly moremassive systems, using the Hubble Space Telescope and ground-based telescopes.The aim of this survey is to probe what physical conditions and processesregulate the emission of Ly alpha radiation on local and global galacticscales. The fact that Ly alpha is a resonant line makes it optically thick evenat relatively low neutral hydrogen column densities, this means that theradiative transport of Ly alpha photons through galaxies is a complex problemwhere the structure, kinematics and dust content, and neutral hydrogen contentof the interstellar medium all contribute to the process. In this talk I willpresent unique HST Lyman alpha maps and FUV spectroscopy of 44 galaxies within theLARS sample.  Roughly half of the sample are dwarf galaxies (with stellar masses lower than one billion solar masses) and they are all highly star-forming. These galaxies show, on average, a higher Lyman alphaescape fraction than the rest of the sample.  By comparing global observables(e.g., SFR, extinction, Lyman alpha line profile, Lyman alpha morphology, HI mass)to the Lyman alpha escape fraction I will try to explain why the physicalconditions in these dwarf galaxies makes it easier for Lyman alpha photons to escape. Detectingdwarf galaxies at high redshift is often only possible by Lyman alpha emission,which makes understanding how the emission escapes critical for interpretingthe observations in a broader context (e.g., galaxy evolution, re-ionization).

Quantifying the interplay of massive stars and the interstellar medium

Sander, Andreas

A significant part of our view on dwarf galaxies depends on understanding the young, bright, and massive stars in them. Their impact ranges from global quantities, such as the inferred star formation rate from the combined UV or H-alpha emission of a dwarf galaxy, over the chemical evolution due the enrichment with processed elements, down to the shaping of individual structures due to their ionizing and mechanical feedback.To substantially improve our picture of galaxy formation and evolution, the influence of massive stars has to be carefully studied and simulated. As stellar winds are inherent to all massive stars, this task requires a detailed, unified modelling of their outer layers and their winds. For hot stars, this requires complex radiative transfer calculations in an intricate non-LTE situation being performed in parallel with the explicit solution of the statistical equations for hundreds of atomic levels. Consequently, less than a handful of codes exist worldwide that are capable of performing this task for an expanding atmosphere with a line-driven wind. One of the most advanced among them is the Potsdam Wolf-Rayet (PoWR) code, nowadays applicable to hot stars of all kinds. The immense detail of the models allows applications drawing theoretical conclusions from models as well as the measurement of stellar parameters and feedback.Using PoWR as an example, this talk will give a brief summary about quantifying the impact of hot, massive stars with the help of modern atmosphere models. Apart from outlining the underlying physics that need to be taken into account, also challenges and powerful applications will be discussed, such as pinpointing the most important influencers in a cluster or predicting the spectral apperance of an unresolved stellar population. The talk will close by giving a brief overview of recent and oncoming applications that will allow to connect loose ends between the fields of massive stars and dwarf galaxies.

Baryonic feedback in scalar-field dark matter halos: dwarf galaxies as cosmological probes to constrain the nature of dark matter

Rindler-Daller, Tanja

The standard cold dark matter (CDM) paradigm has been challenged over the years, where discrepancies have been found between the predictions of CDM simulations and observations of galaxies, particularly dwarf galaxies: the cusp/core problem of dark matter density profiles, the predicted overabundance of Local Group satellite galaxies, and the too-big-too-fail problem.  Scenarios have been invoked to resolve these problems through the additional effectsof baryonic physics, but they generally require strong feedback processes which may not be sufficient in all cases. Meanwhile, attempts to detect the standard CDM particle candidate WIMPs have so far failed. As a result, interest in alternative dark matter has increased, to resolve the small-scale structure issues of standard CDM while retaining its successes on large scales. Dwarf galaxies constitute a powerful probe to study such alternative models.We consider a class of models - scalar-field dark matter (SFDM), where all of the dark matter is comprised of ultralight bosons (m>~10^(-22)eV). SFDM dynamics differs from standard CDM on small scales, suppressing structure formation below a characteristic scale, thereby providing a possible cure to the above problems. This introduces novel effects with observable consequences, including the flattening of central halo density profiles. However, baryonic physics affects the observational constraints on dark matter particle parameters, and that impact depends upon galaxy formation history and halo mass. In this work, we thus consider the consequences of coupling SFDM to thebaryonic component, including baryonic dissipation and feedback. These effects will be addressed by a hierarchy of methods, from analytical models, to 1D numerical hydrodynamics, to simulationswhich incorporate a 2-phase interstellar medium and evolving chemical abundances and stellar populations. The implications of these results for SFDM as an alternative to standard CDM will be assessed.

High sSFR galaxies: Main Sequence outliers or the new "normal" at high-z?

Gonzalez, Valentino

The main sequence of star forming galaxies has become one of our maintools to study galaxy evolution. This Mstar vs. SFR correlation holdsfor most star forming galaxies throughout the history of the Universe,so much so, that we often call galaxies belonging to the MS, "normal".This is especially true at high-z when most galaxies were actively starforming. While Mstar estimates are fairly robust, the SFR is moresensitive to the many assumptions that go into SED modeling. At z~2, SEDmodeling with standard assumptions yields a small fraction (<25%) ofgalaxies that are better fit with extreme models having very high sSFR,low extinction, and young ages (<30 Myr). The fraction of outliers isespecially high among dwarf galaxies (log(m/msun)<8) and at high-z.Depending on the assumptions the majority of sources at z~6 could beoutliers, bringing into question our use of the term "normal galaxy". Itis possible that the extreme models are just an artifact of SED modelingdue to unsuitable modeling assumptions. For example, the typical SFH ofthese galaxies could be very different to the ones assumed in standardmodels. Other more interesting alternatives include a higher fraction ofbinarity in their stellar populations and/or a top heavy IMF. All ofthese alternatives point to producing more high-energy photons per unitstar formation which has important consequences for the study of cosmicreionization. Unfortunately, broad band photometric data is not adequateto constrain these alternatives but some faint spectroscopic signatures in thefar UV spectrum of galaxies could be key. A few studies have shown thepresence of high ionization emission lines (HILs) in the UV spectrum ofthese MS outliers.  In this presentation we will show preliminaryresults in our systematic search for HILs in MS outliers and theconsequences it has for SED modeling and galaxy evolution, cosmicreionization, and future observability with JWST and thirty meter classtelescopes

Constraining the allowed mass Warm Dark Matter using estimates of the total satellite population of the Milky Way

Newton, Oliver

Surveys of the Milky Way's close environs remain incomplete both in depth and sky coverage, producing only a partial census of its complement of dwarf satellite galaxies. Estimates of this population can be used to place tighter constraints on the allowed masses of candidate Warm Dark Matter (WDM) particles. We present estimates of the total satellite population of the Milky Way (MW) made using observations from both the Sloan Digital Sky Survey (SDSS) Data Release 9 and the Dark Energy Survey (DES) surveys, which together cover nearly half of the sky. These estimates are made by the application of a Bayesian inference method to a set of 5 highly-resolved DM-only MW analogues from the Aquarius simulation suite, and predict fewer satellites than previous studies that only used earlier SDSS data releases. We find only a weak dependence on MW halo mass at fainter absolute magnitudes and predict that half of this total population is potentially observable by the forthcoming Large Synoptic Survey Telescope (LSST). We compare this prediction of the total satellite population in the standard cosmological model to predictions from different WDM cosmologies in order to tighten constraints on the allowed masses of candidate WDM particles.

The star-formation and ionisation properties of low-mass galaxies out to z=1 from ultra-deep MUSE spectroscopy

Paalvast, Mieke

The MUSE instrument on the VLT provides an entirely new way to study the population of, especially dwarf, emission-line galaxies. Here we present results from ~310 hours of GTO observations, spread over ~52 arcmin^2 of the low-mass galaxy population (6<log m*="" msun&lt;9)="" out="" to="" z="1." we="" use="" these="" data="" study="" the="" low-mass="" end="" of="" sfr-m*="" relation="" down="" log="" sfr="" ~="" -3,="" and="" its="" evolution="" with="" redshift,="" sfrs="" determined="" from="" balmer="" lines,="" highlight="" importance="" selection="" function="" on="" inferred="" relation.="" our="" slope="" is="" shallower="" than="" most="" simulations="" semi-analytical="" models="" predict,="" which="" implies="" that="" feedback="" processes="" in="" systems="" affect="" star="" formation="" or="" accretion="" gas="" onto="" galaxies="" are="" more="" important="" expected.furthermore="" ionisation="" properties="" plane.="" particular="" explore="" [o="" iii]="" ii]="" (o32)="" ratio="" has="" been="" argued="" be="" elevated="" non-zero="" escape="" ionising="" radiation.="" discuss="" relationship="" between="" o32="" galaxy="" show="" not="" correlated="" sfr.="" find="" fraction="" extreme="" oxygen="" ratios="" (o32="" &gt;4)="" constant="" implying="" amount="" photon="" over="" cosmic="" time.the="" content="" this="" presentation="" described="" paalvast,="" m.="" (4th="" year="" phd="" student="" at="" leiden="" observatory),&nbsp;="" verhamme,="" a.,="" straka,="" l.a.,="" brinchmann,="" j.="" et="" al="" (submitted="" a&amp;a)&nbsp;and="" boogaard,="" j.,="" bouche,="" n.,="" (in="" prep).&nbsp;&lt;="" log&gt;<="" p=""> </log></log></log></log></log>

A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation

Zhu, Ling

The difficulty of core and cusp problem, comes from the limited number of data points, as well as the degeneracies between the mass profiles and the internal dynamical properties of the tracer stars, velocity anisotropies and internal rotations. We present a new discrete chemo-dynamical axisymmetric modeling technique, which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement over previous Jeans models is that realistic chemical distributions are included directly in the dynamical modelling of the discrete data. This avoids loss of information due to spatial binning and eliminates the need for hard cuts to remove contaminants and to separate stars based on their chemical properties. Using a combined likelihood in position, metallicity and kinematics, we find that our models naturally separate Sculptor stars into a metal-rich and a metal-poor population. The spherical assumption of this galaxy resulted in strong constraint of a cored halo in the literatures. Allowing for non-spherical symmetry, our approach provides a central slope of the dark matter density of gamma = 0.5 +- 0.3. The metal-rich population is nearly isotropic (with beta_r^red = 0.0+-0.1) while the metal-poor population is tangentially anisotropic (with beta_r^blue = -0.2+-0.1) around the half light radius of 0.26 kpc. A weak internal rotation of the metal-rich population is revealed with v_max/sigma_0 = 0.15 +- 0.15.We run tests using mock data to show that a discrete dataset with ~ 6000 stars is required to distinguish between a core (gamma = 0) and cusp (gamma = 1), and to constrain the possible internal rotation to better than 1 sigma confidence with our method.

Using proper motions to constrain the origin of galaxies

Fritz, Tobias

Due to their proximity,  the globular clusters and dwarf galaxiessatellites of the Milky Way can be observed in great detail from theirresolved stars. Proper motions can provide crucial information on theorigin of several of these systems. In this talk we present results usingground based images and Gaia DR2 data to measure the proper motion ofglobular clusters and dwarf galaxies in the halo of the Milky Way. Due toits orbit and metallicity, we find that the Pyxis globular cluster did notform in-situ, but it was likely accreted from an unknown, likely destroyeddwarf galaxy more luminous than M_V=-10. Furthermore, we find that theultra faint Segue 1 was not a satellite of known dwarf galaxies moreluminous than M_V=-8.8 and therefore likely formed on its own without being"a satellite of a satellite". In case of Gaia DR2 data, we concentrate onthe recent discovered ultra-faint galaxies to explore their possibleassociated to the Magellanic clouds and use them to make inferences ontotal mass of the Magellanic clouds.

Metallicity calibrations of low star-forming dwarf galaxies: the influence of a stochastic IMF

Paalvast, Mieke

We present a study of the consequences of an initial mass function (IMF) that is stochastically sampled on the main emission lines used for gas-phase metallicity estimates in low star-forming dwarf galaxies. We use the stochastic stellar population code SLUG and the photoionisation code Cloudy to show that the stochastic sampling of the massive end of the mass function can lead to clear variations in the relative production of energetic emission lines such as [OIII] relative to that of Balmer lines.  We use this to study the impact on gas-phase metallicity calibrators such as the electron temperature method and the N2O2, R23 and O3N2 strong-line methods. We find that the stochastic sampling of the IMF leads to a systematic over-estimate of O/H in galaxies with low star formation rate ($\le 10^{-3}$ \Msun /yr$^{-1}$)  when using all different methods. We point out that while the  SFR(Ha)-to-SFR(UV) ratio can be used to identify systems where the initial mass function might be insufficiently sampled, it does not provide enough information to fully correct the metallicity calibrations at low star formation rates. Care must therefore be given in the choice of metallicity indicators in such systems, with the N2O2 indicator proving most robust of those tested by us.The content of this presentation is described in Paalvast, M. & Brinchnmann, J., 2017, MNRAS, 470, 1612

Resolving the Origin of GAMA’s Enigmatic Dwarf Galaxies

Moffett, Amanda

The GAMA survey’s dwarf “Little Blue Spheroid” (LBS) galaxy class has a complex identity, combining star formation typical of spiral galaxies with elliptical-like morphology. Using deep, high-resolution imaging from VST KiDS and the Bayesian, two-dimensional galaxy profile modeling code ProFit, we examine the detailed structure of LBSs and find structural properties similar to low-mass elliptical galaxies. In contrast to this apparent spheroid-like structure, SAMI survey integral field spectroscopy data indicate that LBS dynamics are rotation dominated, or disk like. We also find that LBSs typically occupy low group halo mass environments similar to those of low-mass spiral galaxies. Finally, we consider potential origin scenarios for a population with this unexpected combination of properties, which include star-forming, field-environment precursors to dwarf ellipticals, products of dwarf-dwarf mergers, and transitional dwarf starbursts akin to blue compact dwarf galaxies.

Chemodynamical simulations of dwarf galaxies

Kobayashi, Chiaki

Using our chemodynamical simulations that include star formation, supernova feedback, and detailed chemical enrichment, we show our zoom-in simulations of satellite galaxies in the Milky Way-size halo. Our simulations are in good agreement with the observed metallicity distribution of stars as well as the evolution of elemental abundance ratios. This story is coupled with the detailed modelling of Type Ia Supernovae (SNe Ia), and we also show the impact of the subclasses of SNe Ia, namely, sub-Chandrasekhar mass SNe Ia and so-called Type Iax SNe.

A 3.5-million Solar Masses Black Hole in the Centre of the Ultracompact Dwarf Galaxy Fornax UCD3

Afanasiev, Anton

The origin of ultracompact dwarfs (UCDs), a class of compact stellar systems discovered two decades ago, still remains a matter of debate. Recent discoveries of central supermassive black holes in UCDs likely inherited from their massive progenitor galaxies provide support for the tidal stripping hypothesis. At the same time, on statistical grounds, some massive UCDs might be representatives of the high luminosity tail of the globular cluster luminosity function. Here we present a detection of a 3.5±1.4 × 106 MSun black hole (1s uncertainty) in the centre of the UCD3 galaxy in the Fornax cluster, that corresponds to 4% of its stellar mass. From Jeans dynamical modelling of the UCD3 internal kinematics obtained with the SINFONI spectrograph at the ESO Very Large Telescope using adaptive optics, we rule out the zero black hole mass at the 3s confidence level. This is the fourth supermassive black hole found in a UCD and the first one in the Fornax cluster. Similarly to other known UCDs that harbour black holes, UCD3 hosts metal rich stars enhanced in a-elements that supports the tidal stripping of a massive progenitor galaxy as its likely formation scenario. We estimate that up to 80% of luminous UCDs in galaxy clusters host central black holes. This fraction should be lower for UCDs in groups, because their progenitors are more likely to be dwarf galaxies, which do not tend to host very massive black holes upon formation.

Dense star formation in metal-poor galaxies: an ALMA perspective

Goncalves, Thiago

In this talk, I will present the result of an observational project using ALMA to investigate the properties of the molecular gas in low-redshift (z~0.2) ultraviolet-luminous galaxies. These objects are extremely dense, highly star-forming and very metal-poor compared to other galaxies of similar stellar mass at the same redshifts, justifying their use as analogues to distant main-sequence galaxies in an attempt to understand the interplay between gas and star formation under similar conditions in the early universe. We have observed the most metal-poor objects in our sample, in order to determine whether metallicity plays a role in CO emissivity of the molecular regions in galaxies down to 10^9 solar masses. Our four non-detections, with stringent upper limits, show that CO is severely depleted, even under turbulent conditions. We discuss the implication for observations of sub-L* galaxies at high redshift, which are considerably more metal-poor than objects with similar stellar masses in the local universe.

Star formation across the metallicity ladder in the local group dwarf Magellanic system

Kalari, Venu

We present resolved multi-wavelength observations of molecular clouds, young stellar objects, and pre-main sequence stars (the latter two limited to stars more massive than a solar mass) in the local group dwarf galaxies the Large (1/5 Zsun), Small (1/10 Zsun), and the Magellanic Bridge (1/10 Zsun). From these, we compare our results with those in the Galaxy to demonstrate how there are noticeable differences in key star formation indicators, and also the effect of feedback from massive stars across the metallicity ladder- which may provide vital clues as to how star formation proceeded in the early Universe.

Evolved stars of Local Group galaxies IC10 And IC1613

Di Criscienzo, MArcella

Evolved stars are drivers of galactic chemical enrichment and evolution. In particular, asymptotic giant branch (AGB) stars play a crucial role in the determination of the recent  star formation history. Being main dust manufacturers, they are also essential to understand the stellar contribute to the dust budget of the environment where they form. A multi-wavelenght approach, that includes near and mid-IR infrared observations to detect the dust-enshrouded AGB stars, is fundamental to achive these goals. Currently, resolved mid-infrared stellar population studies of galaxies are limited to nearby galaxies (d<1.5Mpc). James Webb Space Telescope (JWST) will revolutionize this field by vastly expanding the volume over which this kind of studies can be conducted. Waiting for the launch of JWST, our group has started a project on the interpretation of evolved stars in the DUSTiNGs targets (Boyer et al., 2015) starting with the dwarf galaxies IC10 and IC1613. In this talk I will show how our models of thermally-pulsing AGB stars, that also describe the dust-formation process in the wind, are able not only to characterize in term of mass and metallicities their AGB population but also to retrive important information about their star formation histories and dust production rate.

A Massive Stellar Feedback Driven Outflow from the Small Magellanic Cloud?

McClure-Griffiths, Naomi

Feedback from massive stars plays a critical role in the evolution of the Universe by driving powerful winds out of galaxies which can enrich the intergalactic medium and regulate star formation within galaxies. As the most numerous galaxies in the Universe, dwarf galaxies may be important candidates for populating the intergalactic medium with enriched gas. Although star formation rates in dwarf galaxies can be lower than their more massive, starburst counterparts, these low mass systems have small gravitational potential wells and thereby find it difficult to maintain their star-forming material in the presence of intense stellar feedback.  Here we use new data from the Australian SKA Pathfinder to show that the nearest low metallicity, gas rich dwarf galaxy, the Small Magellanic Cloud, shows evidence of stellar feedback driven outflows.  The outflow is made up cold filamentary material extending up ~1 kpc, with temperatures of T< 500 K and widths as small as 50 pc.  We estimate a significant atomic gas mass flux in the range 0.2 - 1 solar mass per year, which may be feeding the Magellanic Stream.

Neutral Gas Phase Metallicities in Gas Associated with Dwarf Galaxies

Rao, Sandhya

Since small columns of metals are easily detected in absorption, observations of quasar absorption-line systems are powerful probes of metal abundances in foreground gas associated with galaxies. For predominantly neutral gas, with N(HI) > 1019 atoms cm-2, metallicities as low as [X/H] > -3 can be measured. At redshifts z < 1, the observed range of metallicities in neutral-gas systems mostly spans -1.5 < [X/H] < 0.5. These same systems have also been imaged with the aim of finding the associated galaxies. Although luminous galaxies are sometimes found to be along the quasar sightline, usually the best candidate for an absorbing galaxy must be a dwarf with luminosity < 0.1L*. Even in cases where luminous galaxies are found within an impact parameter of 100 kpc of the quasar sightline, it is virtually impossible to rule out the possibility that the sightline passes through gas in an unseen dwarf.In this contribution we discuss metallicity measurements in predominantly neutral-gas quasar absorption-line systems, which we conclude are strongly associated with dwarf galaxies. We also discuss a selection bias which indicates that the current estimate of the mean neutral-gas-phase metallicity may be over-estimated by up to a factor of 4. 

Studying gas-rich dwarf galaxies with the minihalo model

Faerman, Yakov

Over the last decade, sensitive surveys in the 21-cm have revealed a population of isolated Ultra-Compact High-Velocity HI Clouds (UCHVCs). Some of these objects were suggested as potential dwarf galaxy candidates. Deep optical observations have been carried out to search for associated stellar populations, and have lead to the discovery of several ultra-faint dwarfs (Leo P, Pisces A & B, SECCO 1), allowing mass and distance measurements. Together with other dwarf galaxies in the Local Volume, they allow us to address various problems, such as star formation in different regimes, physical processes important for structure formation and evolution, and maybe provide hints for the nature of dark matter (DM). However, many HI-selected galaxy candidates may harbor only small numbers of stars or none at all.In our work we develop methods to study the properties of dwarf galaxies and galaxy candidates using 21-cm observations. We model their gas distributions using the minihalo model (Sternberg, McKee and Wolfire 2002), as gas clouds in hydrostatic equilibrium in DM halos, heated and ionized by the metagalactic radiation field. In Faerman, Sternberg and Mckee 2013 we show that high-resolution 21-cm observations (such as those carried out by Adams et al. 2016) can be used to estimate (presently unknown) distances to the UCHVCs. Alternatively, if the distances to them are measured by some other method, HI column density profiles can be used to constrain the DM halo properties. We use 21-cm observations of Leo T as a test case for our methods. In a follow-up work (Faerman, Goettlib and Sternberg, in prep.) we model new, deep HI observations of Leo T (Adams and Oosterloo, in press) to estimate the pressure of the intergalactic medium in the Local Group. Application of our methods to future 21-cm observations from instruments such as EVLA, APERTIF, ASKAP and SKA will allow us to realize the potential of gas-rich, ultra-faint galaxies as astrophysical laboratories.

Exploring the Role of Dwarf Galaxies at High Redshift through JWST NIRSpec+NIRCam Instrument Team GTO Observations

Bunker, Andrew

I will discuss the prospects for studying dwarf galaxies at high redshift with the James Webb Space Telescope (JWST). Since the initial discovery in 2003 of galaxies at z>6 (within the first billion years) using the Hubble Space Telescope and the Lyman break technique, it has become clear that the rest-frame UV luminosity function (LF) has a much steeper faint-end slope at high redshift than in the more recent past, and hence the fainter but more numerous galaxies dominate the UV photon production of the Universe. Faint galaxies below our current detection limits with Hubble may be responsible for reionzing the universe - although this calculation depends critically on the escape fraction of ionizing photons (which is currently unconstrained). JWST will revolutionise our understanding, by probing significantly fainter to better determine the LF faint end slope, and observing out to 5microns with NIRCam & NIRSpec to sample the rest-frame optical out to z~10. This will enable the stellar mass function to be determined as well as the rest-UV LF. Our JWST Advanced Deep Extragalactic Survey (JADES) is a joint program of the JWST/NIRCam and NIRSpec Guaranteed Time Observations (GTO) teams involving 950 hours of observation targetting the CANDELS GOODS-North and South fields (including the Ultra Deep Field).  The deepest NIRCam images are 50ksec in 9 filters (from 0.9-4.5microns) and will cover ~46square arcmin down to AB~31mag (5sigma), with multi-object NIRSpec spectroscopic follow-up of 100ksec in the low-dispersion R=100 mode (1-5 microns) and observations at higher spectral resolution (R=1000 and 2700). Emission line ratios will determine extinction, metallicity, ionization parameter and the escape fraction of ionizing photons (by comparing the Balmer recombination lines with the rest-frame UV). Understanding the contribution of line emission will enable stellar population fits to the multi-wavelength photometry of dwarf galaxies at z>6 for the first time.

Testing one-zone chemical evolution models against hydrodynamics simulations of Local Group dwarf galaxies

Escala, Ivanna

We can potentially distinguish between different star formation and mass growth histories by applying galactic chemical evolution models to detailed observations of chemical abundances in dwarf galaxies. However, typical shortcomings of one-zone chemical evolution models, such spatial chemical homogeneity, may limit the predictive power of such models. We test the ability of one-zone chemical evolution models to match predictions from cosmological, hydrodynamics simulations of dwarf galaxies from the Feedback in Realistic Environments (FIRE) project in the mass range M$_{\star}$($z$ = 0) $\sim$ 7 $\times$ 10$^{5}$ - 2 $\times$ 10$^{8}$ M$_{\odot}$. Building off ofthe Kirby et al. chemical evolution model, which incorporates gas accretion, supernovae-driven mass loss, and tracked abundances from Types Ia and II supernovae, we introduce additional physics (e.g., alterations to the Ia delay time distributions, enriched gas accretion events) to improve agreement with the FIRE simulations.  We determine the best-fit model parameters for the simulated dwarf galaxies using Markov chain Monte Carlo methods, and derive their star formation and mass growth histories from their simulated $\alpha$-element abundance patterns. Additionally, we apply the chemical evolution model to observed chemical abundances in Milky Way and M31 satellite galaxies to compare model predictions against observations. By contrasting results from chemical evolution models with the known evolutionary history of the simulated dwarf galaxies, we quantify the degree to which one-zone models can reliably be applied to Local Group dwarf galaxies.

Dense molecular gas in dwarf galaxies: views from the outer disks and M33

Gao, Yu

The dense molecular gas mass, traced by HCN J = 1-0, linearly correlates with the far-infrared (FIR) luminosity (~ star formation rate, SFR) for essential all star-forming systems near and far. The spatially resolved FIR-HCN correlation in the spiral disks of galaxies, a local star formation law in terms of dense molecular gas across the disks, is also established, to be essentially same as that established from the Galactic cloud cores and that of global galaxies. Such tight linear SFR - dense molecular gas correlations suggest that the SFR depends linearly uponthe mass of dense molecular gas. This is drastically different from the traditionally established Kennicutt-Schmidt (K-S) laws that relate the total gas and SFR in galaxies as there are no unique correlations in these K-S laws. Will this FIR-HCN correlation be still valid and applicable in dwarf galaxies? The difficulty in detecting CO in dwarf galaxies with  ALMA already implies that it is almost impractical in detecting the HCN emission in more a few dwarf galaxies. Nevertheless, HCN observations in M33 and the outer disks of star-forming galaxies, e.g., M51, indeed show that the dwarf galaxies should follow the same linear FIR-HCN correlation over 10 order-of-magnitude. Finally, we also report the progress of our efforts in ALMA observations of dense gas in a nearby dwarf galaxy.

Internal dynamics of dwarfs around the Milky Way

del Pino, Andres

Dwarf galaxies in the Local Group have been consistently studied over almost a century now. Numerous data have been collected about their stellar content, line-of-sight velocities, and many of their internal structural parameters. However, it has not been until the last decade when the tangential velocities of their stars (proper motions) have been also within reach. For the moment, only the unparalleled astrometric precision of the Hubble Space Telescope has allowed to derive the bulk proper motions of some dwarf galaxies, providing the appropriate rest frame for analyzing their internal dynamics. With the advent of GAIA, new data is becoming available, opening the door to state-of-the-art dynamical studies. In this talk we will present new internal dynamics results for dwarfs making use of these recent observations and novel analysis techniques.

Stellar feedback in the Blue Compact Dwarfs ESO338-IG04 and Haro 11

Bik, Arjan

Luminous blue Compact galaxies are local strongly star-forming dwarf galaxies. They host dozens of super star clusters and are considered to be analogues of high redshift dwarf galaxies. These galaxies give us the unique laboratories to study the effect of feedback from super star clusters on the interstellar medium, determine the conditions under which they become Lyman continuum leakers and help probing the role that high-redshift dwarf galaxies play in the re-ionization of the universe.We present deep optical  integral field spectroscopy with VLT MUSE of two local blue compact dwarf galaxies ESO 338-IG04 and Haro 11. The MUSE datasets reveal that the galaxies are embedded in extended halos of ionized gas. Analyses of the ionized gas, using optical forbidden emission lines, reveal that Wolf-Rayet dominated super star clusters are responsible for creating ionization channels extending all the way to the edges of the halo, possibly facilitating the escape of Lyman Continuum photons. We also find evidence for chemical enrichment by the Wolf-Rayet stars.In particular we find evidence for supernovae induced feedback in the shape of a superbubble and a galactic scale outflow in ESO 338. Analysis of the spatially resolved BPT diagram reveals the presence of shocks around the central starburst as well as the location where the outflow meets the more quiesence gas in the galaxy halo.Finally, using the high quality MUSE observation of local dwarf galaxies, we present simulated observations for ELT/MOSAIC of dwarf galaxies at redshift 1-2 in order to determine what physical parameters of the halo we can derive at those redshifts with the next generation of telescopes. 

Dwarf galaxies as hosts of massive explosions - a view in 3D

Thöne, Christina

Massive stars are connected to highly star-forming environments and galaxies, and hence are their explosive deaths. Gamma-ray bursts (GRBs) and superluminous supernovae (SLSNe) are the most luminous of those stellar explosions. Both classes of objects are hosted in starburst galaxies with low metallicities and young stellar populations, which, at redshifts below 1-2 are mostly dwarf galaxies. Integral field data now allow us to study the most nearby and brightest of them with resolved spectroscopy. Here, we present a sample of z<0.5 GRB hosts observed with FLAMES and MUSE to study their spatially resolved abundances, star-formation (SF) and kinematics. GRBs are usually found in regions with low metallicity and high star-formation rate, but not at the site with the most extreme properties. In fact, most are located at the edge of the most extreme region in their host. The kinematics of these galaxies mostly do not show evidence for SF triggers due to major interactions or merger. However, we do find evidences for outflows from these galaxies, underlining the extreme SF activity. Last, we also present the curious case of a seemingly solar metallicity SLSN host and SLSN environment, where star-formation history modeling reveals the contribution of a young low-metallicity population, the likely origin of the SLSN progenitor.  This shows that detailed 3D studies are crucial, not only for the hosts of massive stellar explosions but for understanding the star-formation history and triggers of dwarf galaxies in general.

Studying dwarf galaxies up to very high redshift using gamma-ray bursts

de Ugarte Postigo, Antonio

Long duration gamma-ray burst are produced by the explosive death of short lived, very massive stars. Thanks to their extreme luminosities, they can be detected at basically any redshift (being the spectroscopic record z=8.2). Consequently, they are good tracers of the star formation throughout the Universe’s history. They can be detected and their redshifts measured independent of their host luminosity. In fact, many of the hosts of GRBs have been found to be dwarf galaxies that would have been missed in regular galaxy surveys. In this sense, GRBs are one of the few and most efficient methods of studying dwarf galaxies at very high redshift.Here I will present a study of the properties of the galaxies in which gamma-ray bursts are produced. I will do so from different perspectives: From their inside, through absorption spectroscopy, which allows us to measure the composition, dynamics and structure of cold gas within the galaxy. From their emission spectra, when the galaxies are bright enough (typically up to z=3.5), which allows us to use strong line diagnostics. From spectral energy distribution studies, which allows us to determine host galaxy properties up to higher redshifts (up to z~5).The datasets used for this work include the SHOALS sample of GRB host galaxies (the most extensive sample to date) and the GRB spectra stored in the GRBSpec database that we manage, including data from FORS and X-shooter at the 4x8.2m VLT (Chile) and OSIRIS at the 10.4m GTC (Spain). 

Kinematics of Quenched Dwarf Galaxies: Differentiating Quenching Mechanisms Across Environments

Dickey, Claire

While it has long been understood that both environmental and internal processes play important roles in quenching galaxies, the relative importance of the two categories remain poorly understood, particularly for low-mass galaxies. In this work, we look for signatures of external vs internal quenching of low-mass quenched dwarf galaxies in isolation and cluster environments by examining stellar kinematics derived from high-resolution optical spectroscopy. In particular, we investigate the lowest-mass quenched galaxies which exist in isolation (M* = 10^(9-9.5) M_sun; Geha et al., 2012). These galaxies may represent the lowest stellar mass population in which internal feedback effects are still able to quench galaxies. We compare this sample to corresponding quenched galaxies in the Virgo Cluster within our mass range of interest, as well as a sample of low-mass star forming galaxies in isolation. All 40 galaxies in our study were observed with the Keck/ESI spectrograph, making this a uniquely self-consistent dataset across a range of environments and star formation rates. We find that isolated quenched and star forming galaxies show kinematics consistent with being rotationally-supported, while cluster galaxies are primarily dominated by random motions. Based on the existence of distinct kinematic signatures of isolated vs cluster dwarf galaxies, we constrain the nature and efficacy of feedback processes for quenching galaxies at low stellar masses.

Very gas-rich extremely metal-poor blue void dwarfs

Pustilnik, Simon

Half-dozen of extreme representatives of void dwarf galaxy population werefound in our study of evolutionary status of a hundred galaxies in the nearbyLynx-Cancer void. They are very gas-rich, extremely low-metallicity[7.0 < 12+log(O/H)<~7.3] objects, with blue colours of outer parts. Thecolours indicate the ages of the oldest visible stellar population of one toa few Gyr. They all are intrinsically faint, mostly LSB, with M_B range of-9.5 to -14 mag. Thus, their finding is a subject of the severe observationalselection. The recent advancement in search for such objects in other nearbyvoids resulted in doubled their total number. We summarize all available dataon this group of unusual void dwarf galaxies and discuss them in the generalcontext of very low metallicity galaxies and their possible formation andevolutionary scenarios.

The detection of abundant cold methanol gas in the Small Magellanic Cloud

Shimonishi, Takashi

Observations of organic molecules in metal-poor systems will provide crucial information for understanding chemical processes in high-redshift galaxies where the metallicity was significantly lower than the present solar neighborhood. The Small Magellanic Cloud (SMC) is a nearby star-forming dwarf galaxy, whose metallicity is lower than typical Galactic values by a factor of five. We here report the first detection of a complex organic molecule, methanol (CH3OH), in the SMC based on submillimeter observations towards a high-mass young stellar object with ALMA. Besides CH3OH, we also detect the dust continuum as well as emission lines of CS, C33S, H2CS, SO, SO2, H13CO+, H13CN, SiO, and tentatively HDS from the observed region. The target infrared point source is spatially resolved into two dense compact sources; one is associated with an embedded high-mass young stellar object, another is not associated with an infrared source but shows rich molecular lines. The first detection of CH3OH in the SMC has a strong impact on the formation of complex organic molecules in metal-poor environments. The fractional abundance of CH3OH gas in the observed dense cloud is estimated to be (0.5--2) x 10^-8, which is comparable with those of similar Galactic cold sources despite a factor of five lower metallicity in the SMC. This would indicate an enhanced production or a suppressed destruction of gas-phase CH3OH in the observed SMC source compared to Galactic counterparts. The gas temperature is estimated to be about 10 K based on the rotation analysis of CH3OH lines, suggesting that non-thermal desorption would contribute to the production of the observed CH3OH gas. This work provides observational evidence that an organic molecule like CH3OH, which are largely formed on grain surfaces, can be produced even in a significantly lower metallicity environment compared to our Galaxy. 

Henize 2-10: A Dwarf Irregular with a Massive Black Hole or a Supernova Remnant?

Rohr, Eric

Based on radio and X-ray observations, it has been suggested (Reines et al 2011) that a massive black hole resides in the low mass dwarf irregular galaxy Henize 2-10. This unusual finding has important implications for the formation of massive black holes in the early Universe since Henize 2-10 can be viewed as a low redshift analog to the first high-z galaxies. We present long-slit HST STIS spectra that pass over the suggested position of the massive black hole, marked by a compact (<3x1pc) 1 mJy radio source observed at 1.4 GHz by the LBA (Reines and Deller 2012). While recent MUSE-IFU spectroscopic observations showed no change in ionization near the radio source, calling into question the existence of an accreting massive black hole (Cresci et al 2017), our higher spatial resolution observations reveal a compact region of significantly lower ionization, with no velocity gradient across 0.1 arcseconds. Preliminary analysis suggests this emission, and the radio emission, are both consistent with a luminous supernova remnant. These observations weaken the case for a massive black hole in Henize 2-10.

Star formation in dwarf galaxies in the ELAIS N1 field

Kovács, Tímea Orsolya

The European Large Area ISO Survey (ELAIS), which was one of the biggest open-time projects of the Infrared Space Observatory (ISO), has covered a total of 12 square degrees on the sky, and measurements were taken in four different bands (in a wavelength range of 6.7-175 µ m). The survey consisted of multiple smaller regions, and one of these regions was the ELAIS N1 field. ELAIS N1 became one of the most known regions on the sky thanks to multiple follow up surveys which were carried out in different wavelength ranges, from the optical to the radio.We have chosen dwarf galaxies in the ELAIS N1 field, and fitted their Spectral Energy Distributions (SED) with the SED fitting code CIGALE (which was developed by the Laboratoire d'Astrophysique de Marseille).We used data from the new Herschel SPIRE and PACS Point Source catalogues, to add data points in the far infrared, so we can constrain the emission of the dust surrounding young stars, and give a better estimation on the star formation rate. Data available in VIZIER from multiple surveys (WISE, SDSS and surveys specific to this region) have also been used.CIGALE can be used in a broad wavelength range, and it is very modular, different modules can be chosen for the different processes and mediums in galaxies. With the SED fittings we determined several parameters of the galaxies, including their star formation rate and dust mass.

The evolution of the luminosity function faint end of cluster galaxies in the Cluster-EAGLE simulation

Negri, Andrea

The galaxy luminosity function (LF) is a fundamental tool for exploring galaxy evolution over cosmic time. In the last decade observations have been able to probe the evolution of the galaxy LF with redshift, in particular showing a variation of its low-mass end with redshift. On the numerical side, there is currently no extended study of the evolution of the LF of galaxies in clusters. We employ the data of the Cluster-EAGLE project, a set of cosmological, hydrodynamical zoom simulations of 30 galaxy clusters, to study the evolution of the galaxy LF in clusters as function of redshift. We compile a catalogue of simulated galaxies’ luminosities in the SDSS bands using the E-MILESspectra database, and taking into account dust attenuation. Stacked luminosity functions show a good agreement with observations, presenting little evolution with redshift of the faint-end slope. The environment effects are strong for intermediate-luminosity galaxies. At radius larger than 3 virial radii, star-forming galaxies dominate in number the knee of the LF, whereas, inside the clusters (r < r200), the fraction of passive galaxies is larger. The relative fraction of passive and star-forming galaxies within r200 evolves with redshift, with the star-forming fraction being larger above z~0.5. Remarkably, the fraction of low-luminosity, red dwarfs dominates the faint end up to z=2.

Modeling Low Mass Stellar Populations

Bruzual, Gustavo

Modeling low mass stellar populations, like clusters and dwarf galaxies, with population synthesis models requires that we evaluate the role played by stochastic fluctuations in the sampling of the IMF on the spectro-photometric properties of these sparse populations. Interacting binaries may also modify the integrated spectra of these systems depending on the final product of the binary interaction and on the frequency of binary stars. In this work we compare the relative importance of stochastic fluctuations and binary evolution on low mass galaxy properties as a function of the stellar IMF, population age, metallicity, and binary fraction. In most cases the effects of stochastic fluctuations dominate those produced by binary interactions. We explore and quantify the relative importance of these effects through cosmic times.

Diffuse post-starburst galaxies: a smoking gun of UDG formation via ram pressure stripping

Chilingarian, Igor

Ultra-diffuse galaxies (UDGs) is a recently identified galaxy type: they have sizes comparable to the Milky Way and stellar masses of about 1/1000 of it. Ultra-diffuse galaxies (UDGs) attracted a lot of attention as possible "dark galaxies" heavily dominated by dark matter, however, no dynamical mass estimates were done because of their extremely low surface brightness. We have recently found 13 gas free diffuse blue post-starburst (300-500Myr) galaxies without ongoing star formation in Coma and Abell2197, which, should they continue to evolve passively, will become UDGs in 5Gyr. Four of them exhibit tails of ram pressure stripped material visible in deep direct images. We followed up three galaxies spectroscopically with GMOS at the 8-m GEMINI-North telescope and Binospec at the 6.5-m MMT and recovered their major axis kinematics and stellar population properties out to 2 effective radii. All three galaxies show a nearly solid body rotation at moderate amplitudes (30-50 km/s). We performed Jeans axisymmetric modelling and showed that observed M/L ratios are consistent with only 30-50% of dark matter in addition to stars and, therefore, these objects are not "dark galaxies" but are normal intermediate to large-sized discs where the star formation was quenched by the ram pressure stripping.

Dwarf galaxies at high redshifts probed by absorption lines

Christensen, Lise

Absorption lines in background objects such as luminous quasars or gamma-ray bursts reveal clouds of intervening gas with relatively low metal enrichments out to high redshifts (z>5). During the past few years we have finally reached the consensus that the strongest Hydrogen absorption lines arise in disks or in the circum galactic medium of galaxies that randomly lie along the line of sight to background sources.Akin to the relation between stellar mass and metallicity seen in emission selected galaxies, we find a similar relation for absorption lines, i.e. the most metal-rich absorbers arise in relatively massive galaxies. Conversely, it means that the majority of absorbers that have around 10% solar metallicities arise in low-mass galaxies. Absorption line spectroscopy therefore harbours information on the physical nature of galaxies from low to high redshifts.I will present the connection between luminosity-selected and absorption-selected galaxies, and demonstrate how absorption lines give complementary information on the evolution of low-mass galaxies, and their circum galactic environment. Finally, I will describe how we can use absorption lines to probe the structure of the dark matter halos of dwarfs at intermediate to high redshifts.

Quenching in the Virgo cluster down to logL = 6 Lsun

Sanchez-Janssen, Ruben

The Next Generation Virgo Cluster Survey (NGVS) has imaged the iconic nearest cluster out to its virial radius in visible and near-infrared wavelengths with unprecedented sensitivity and resolution. This has enabled detailed studies of the galaxy populations down to mass scales only previously probed in the Local Group, but with significantly larger statistical power. In this contribution I will summarise the main findings of the NGVS regarding the properties of cluster dwarf galaxies down to logL = 6 Lsun, with a specific emphasis on the fractions of quiescent and star-forming dwarfs as a function of stellar mass and clustercentric distance. I will discuss the results in the context of environmental quenching efficiencies and timescales in clusters compared to groups at these unprecedented mass scales.

Early chemical enrichment of the Milky Way dwarf satellites from high-resolution and NLTE analysis of VMP stars

Sitnova, Tatyana

Current knowledge of the first stages of star formation in galaxies is still poor. The stellar abundance trends and dispersions of very metal-poor (VMP) stars reveal the nature of the first generations of stars, their masses, numbers, and spatial distribution, the energetics of the explosion of supernovae, and the level of homogeneity of the interstellar medium. The proximity of the Local Group dwarf spheroidal galaxies (dSphs) allows the derivation of chemical abundances with comparable quality as in the Milky Way (MW). The comparison of these galaxies with very different masses, star formation histories, and level of chemical enrichment can provide crucial information regarding the universality of the physical processes at play. We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of about 60 VMP (-4 < [Fe/H] < -2) stars in the seven dSphs and in the MW halo. Our results are based on high-resolution spectroscopic datasets and homogeneous atmospheric parameters. Once the NLTE effects are taken into account, the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax reveal a similar plateau at [alpha/Fe] = 0.3 for each of the alpha-process elements: Mg, Ca, and Ti, similarly to the MW halo. We put on a firm ground the evidence for a decline in alpha/Fe with increasing [Fe/H] in the Bootes I ultra-faint dwarf galaxy (UFD), that is probably due to the ejecta of SNeIa. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. Our three UFDs - Bootes I, UMa II, and Leo IV are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg] = -1.3 and [Ba/Mg] = -1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate a common r-process origin of their n-capture elements.

A New Method to Derive Star Formation Histories in Dwarf Galaxies

Ceponis, Marius

A new method to determine star formation histories of stellar systems, like dwarf galaxies, is presented. The method uses multicolour stellar photometry data of resolved stellar populations. Star formation histories are determined by comparing observed populations with artificially generated ones based on star counts in binned colour-magnitude diagrams. Parameters of synthetic populations are adjusted iteratively to match observations. 2D star formation distributions are acquired by summing-up Bayesian probabilities of stars to belong to various populations. The method has been extensively tested with synthetic galaxies and applied to recover 1D and 2D star formation history of young (t < 500 Myr) stellar populations in the dwarf irregular galaxy Leo A.

A 3D hydrodynamical simulation of a black hole outflow in a dwarf spheroidal galaxy

Lanfranchi, Gustavo A.

It is a known fact that large galaxies harbour central black holes with masses larger than $\> 10^6 \msun $ and that their feedback causes an impact in the evolution of the galaxy and the media. Recently, observations suggested that also smaller galaxies host black holes in their center, but with lower masses (intermediate massive black holes - IMBH). The effects of these objects in the evolution of the dSphs have been so far not analysed. In this work, we present results of a study of the effects of a outflow from an IMBH in the gas dynamics of dSph galaxies by means of a non-cosmological, 3D-hydrodynamical simulation. Assuming an initial baryonic-to-dark-matter ratio derived from the cosmic microwave background radiation and a cored, static dark matter gravitational potential, we evolved the galactic gas distribution over 3 Gyr, taking into account the outflow of a IMBH. The outflow is simulated by the injection of density and velocity in both directions of one of the axis. We explored the density and velocity space-parameter in order to determine in which physical conditions the outflow can propagate through the interstellar medium of the galaxy. We adopted a scenario with an homogeneous medium and another one with the feedback of supernovae to infer the differences in the propagation of the outflow. Our results indicate that in a homogeneous medium the outflow propagates freely in both directions with the same velocity and its capable of removing a fraction of the gas from the galaxy. When the SNe are taken into account, the effect of the outflow is reduced. It is necessary a velocity around 1000 $km.s^{-1}$ and a density larger than 0.003 $cm^{-3}$ for the outflow to propagate. In this conditions, the removal of gas from the galaxy is almost negligible at the end of the simulation.

Nature or Nurture: The formation of compact elliptical galaxies

Kim, Suk

We aim at finding cE galaxies in various environments using SDSS DR12, and studying stellar population of cEs as a function of environments. Based on the typical properties of cE galaxies, we selected cE candidates by restricting that low-luminosity Mg > 19.5 mag, small sizes Re < 700 pc, and high-velocity dispersions σ > 60 km s-1. Since effective radii of cE candidates are mostly smaller than the seeing size of SDSS photometry, we calculated the effective radius by fitting a Sersic profile using GALFIT. In addition, an environmental parameter is computed as distances between cE galaxies and host galaxies (Mr < -21 mag). Mgb values of cEs increase as the distances from the host galaxies decrease. Especially, for cEs close to the host galaxies(\cEW; Dhost < virial radius), the Mgb values are similar to those of massive elliptical galaxies, which is consistent with the previous studies. On the other hand, cEs distant from the host galaxies (cEWO; Dhost > virial radius) lower Mgb values than the conventional cEs. Moreover, the Mgb values of cEWO follow the σ-Mgb relation of elliptical galaxies. This can be explained as a result of different merger histories for differing environments. For example, cEW galaxies are formed by tidal stripping by massive galaxies as suggested by previous studies (stripped origin or nurture), but cEWO galaxies could be linked with high-redshift spheroids (e.g. faint end of red nuggets) which have not evolved into present-day elliptical galaxies. (intrinsic origin or nature).

The hydrodynamic evolution of the gas content in the dSph galaxy Ursa Minor induced by the feedback from types Ia and II supernovae

Caproni, Anderson

Dwarf spheroidal galaxies (dSph) of the Local Group share a similar characteristic nowadays: a very low amount of gas in their interiors. How these galaxies lost their gas contents during their evolution remains a matter of debate in the literature. In this work, we present results from a three-dimensional hydrodynamical simulation of the gas inside an object with similar characteristics of the classical dSph galaxy Ursa Minor. We evolved the initial galactic gas distribution over 3 Gyr, considering the effects of the types Ia and II supernovae, as well as a cored, static dark-matter gravitational potential. The instantaneous supernovae rates were derived from a chemical evolution model applied to spectroscopic data of the Ursa Minor galaxy. Our numerical simulation shows that the amount of gas that is lost due to supernovae feedback varies with time and galactocentric radius. The highest gas-loss rates occurred during the first 600 Myr of evolution. Our results also indicate that types Ia and II supernovae must be essential drivers of the gas loss in Ursa Minor galaxy (and probably in other similar dwarf galaxies), removing a fraction of at least 60 percent of the initial gas mass inside its tidal radius.

Robust profile decomposition for extragalactic spectral line surveys

Oh, Se-Heon

We present a novel algorithm which is based on a Bayesian Markov Chain Monte Carlo (MCMC) technique for performing robust and reliable profile analysis of a data cube from either single dish or interferometric radio telescopes. It fits a set of models comprised of a number of Gaussian components given by the user to individual line-of-sight velocity profiles, then compares them and finds an optimal model based on the Bayesian Inference Criteria computed for each model. The decomposed Gaussian components are then classified into bulk or non-circular motions as well as kinematically cold or warm components. The fitting based on the Bayesian MCMC technique is insensitive to initial estimates of the parameters, and suffers less from finding the global minimum in models given enough sampling points and a wide range of priors for the parameters. It is found to provide reliable profile decomposition and classification of the decomposed components in a fully automated way, together with robust error estimation of the parameters as shown by performance tests using an artificial data cube. This is an essential feature for profile analysis of the large number of data cubes expected in Square Kilometre Array (SKA) pathfinder surveys. We then apply the newly developed algorithm to a combined HI data cube of the Large Magellanic Cloud (LMC) from the Australia Telescope Compact Array (ATCA) and Parkes radio telescope. The results show highly complex HI structure and kinematics in the galaxy.

Sporadic r-process events found in the Draco dwarf spheroidal galaxy

Tsujimoto, Takuji

One of the last frontiers in nuclear astrophysics is identifying the origin of elements produced through the rapid neutron-capture process (r-process). Although modelling of core-collapse supernovae  and compact object mergers has been intensively conducted as plausible candidates of the r-process site, no evidence for these events has been thus far obtained by direct observations. On the other hand, recent studies support that stellar record on elemental abundances in faint satellite galaxies is crucial to assess its nature because such small stellar systems could be significantly affected by a single r-process event, as found in the ultra-faint dwarf galaxy Reticulum II. The smallness of the systems, however, prevents us from collecting a sufficient number of stars from individual satellites. Hence, it remains unclear whether the discovery of a remarkable-r-process-enrichment event in the Ret II catches the nature of r-process or an exception. Here we report on r-process abundances obtained by high-resolution spectroscopy for twelve metal-poor stars in the Draco dwarf spheroidal galaxy in a narrow metallicity range of -2.5<[Fe/H]<-2. We find that these stars are clearly separated into two groups by r-process abundances with a difference by one order of magnitude. Our finding suggests that the high r-process group is formed by a sporadic r-process event, indicating that a sporadic event discovered for the Ret II is not unique but is also found for the Draco. In addition, the r-process feature at less metallicity, i.e., for earlier epochs of the Draco, implies the presence of at least one separate event lifting a primordial r-process abundance to that close to the low r-process group. Including the object with no detection of r-process elements by previous study, we identify three populations with different r-process abundances, built by two r-process events enriching gases with more than one-order different levels, one of which is not found in the Ret II.

Dwarf Irregular Galaxies and Massive stars: the beginning of a beautiful friendship

Garcia, Miriam

The comunity of massive stars is thrilled about Local Group dwarf irregular galaxies (dIrr). They are a wealthy reservoir of metal-poor massive stars that provide us with unique insight on their medium-to-high redshift relatives, allowing us to assess feedback through cosmic history and to interpret the farthest, most energetic SNe and GRBs. Along the way, we are becoming interested in the recent star-formation history and initial mass-function of the host dIrr's, their chemical evolution, their gas and dust content, and the interplay with hot massive stars. This poster is a showcase of some results on the galaxies that are attracting most of our attention, to stimulate interaction and future collaborations/sinergies between both communities.

Metallicity gradients in local strong line emitters

Shim, Hyunjin

We investigate the spatially resolved chemical abundance distribution of ionized gas emission in local "Halpha emitters" of which Halpha equivalent width as large as that of strong star-forming galaxies at z>4. Most of the galaxies have flat metallicity gradient which is expected to be the result of the metallicity mixing. Based on the emission line ratios, most Halpha emitters lie in the region of a low-metallicity HII galaxies, yet are also explained by the low metallicity AGN with high ionization parameter.

Where did different characteristics of dwarf galaxies come from?

Chun, Kyungwon

We investigate cosmological evolution of isolated dwarf galaxies in the Lambda-Cold Dark Matter model. For this, we modified a cosmological hydrodynamic code, GADGET-3, in a way that includes gas cooling down to T~10 K, gas heating by universal reionization, UV shielding for high-density regions of nshield > 0.014 cm-3, star formation in the dense regions (nH > 100 cm-3), as well as mass, energy, and metal feedback by supernova explosion. We perform four different zoom simulations targeting dwarf galaxies whose total mass is ~1010 Msun. Although four galaxies have similar total mass at z=0, their morphologies, star formation activities, and baryonic properties are very different to each other. In this study, we aim to trace where the differences originate.

Bright-Red Stars in the Dwarf Irregular Galaxy Leo A

Lescinskaite, Alina

We have studied bright-red stars (i.e., stars that are brighter and redder than the tip of the red giant branch (TRGB) in the colour-magnitude diagram I vs. V – I) in the dwarf irregular galaxy Leo A using multicolour photometry data obtained with the Subaru, HST ACS, and Spitzer telescopes. We developed a reliable method to significantly reduce a number of contaminating foreground Milky Way stars, which allowed us to study a spatial distribution of the bright-red stars within the Leo A galaxy and compare it with the distribution of RGB stars. We demonstrated a possibility to distinguish between different types of bright-red stars solely by using multicolour photometry data.

Non-parametric SED fitting of galaxies and measuring of their star formation histories

Shao, Zhengyi

A new approach is built to modeling the SED of galaxies including their photometric passband observations and Lick index from spectroscopic data. This method is based on a construction of the non-parametric star formation history (SFH) which is divided into discrete time intervals and fitting   the average rate of star formation in each interval. Based on the Bayesian framework, the full probability density functions of the fitting star formation rates are obtained and it is flexible to reconstruct these rates to some new parameters, such as the total stellar mass, time scale of the SFH, recent SFR, etc. The method is validated by applying it to monometallic synthetic photometric catalogues created with different input SFHs, assessing how the accuracy of the recovered stellar masses and SFHs depend on the photometric passband set, signal-to-noise ratio and redshift. The results show that it is possible to distinguish an early burst of star formation from a late one, provided an appropriate passband and Lick index set is used. Moreover, the Bayesian Evidence is used to assess the synthetic spectral libraries and the initial mass functions.  Fitting results of Local group dwarfs are discussed. 

KK69: a dwarf galaxy in transition?

Saponara, Juliana

Here we present new HI data of the dwarf galaxy KK 69, obtained with the Giant Metrewave Radio Telescope (GMRT). While optical images of KK 69 suggest it is a faint dwarf spheroidal galaxy, our high-resolution GMRT maps reveal the presence of a considerable amount of HI offset from the stellar body, indicating it may be a transitional dwarf galaxy. Tidal interactions between KK 69 and the nearby spiral galaxy NGC 2683 may be responsible and are being investigated. Furthermore, we are able, for the first time in this galaxy, to separate the cold and the warm neutral phases of the interstellar medium using a Gaussian decomposition method and a stacking routine. We will discuss our results taking into account the relation between the interstellar medium and the star formation activity in the galaxy, the role played by the environment and the influence of these phenomena in the galaxy's evolution.

Spatial distributions of different metallicity groups in red giant branch of dwarf spheroidal galaxies

Han, Sang-Il

The Ca-by photometry of Galactic three dwarf spheroidal galaxies (Draco, Sextans, and Canes Venatici I) obtained from Subaru/Suprime-Cam is presented to study spatial distributions of the red giant branch (RGB) stars according to the metallicity. Due to the sensitivity of the Ca filter to the metallicity, metal abundance of the redder RGB stars in the hk index [=(Ca-b)-(b-y)] are larger than that of the bluer RGB stars and the width of the RGB in the hk index is broader than other colors. We show that the metallicity is correlated with the hk index from the comparison with theoretical isochrones as well as the spectroscopic data in the literature. This suggests that this index can serve as an alternative metallicity indicator and allow us to study the structural feature of different metallicity groups of stars for the relatively larger sample compared to spectroscopy. We present the spatial structure of metal-rich and metal-poor RGB groups defined from the hk index and discuss chemo-structural complexities in the context of dwarf galaxy formation theories.

Tentative Discovery of a Star Cluster Remnant in the Sextans Dwarf Galaxy

Kim, Hak-Sub

We report a discovery of a possible relic of a star cluster in the Sextans dwarf spheroidal galaxy. Using the hk index (=(Ca-b)-(b-y)) as a photometric metallicity indicator, we have successfully discriminated the metal-poor and metal-rich stars in the galaxy and found an unexpected number density peak of metal-poor stars near the galaxy center. The stars around the peak form a narrow sequence in optical color-magnitude diagrams and exhibit redder colors than the bulk of field stars in the galaxy. Our population models suggest that they appear to be originated from an old, metal-poor globular cluster. This supports the presence of the star cluster remnants in the galaxy which have been suggested by previous studies, and provides a piece of evidence of a cored dark-matter halo profile for the Sextans dwarf galaxy. We will discuss the implications of our results for the dwarf galaxy formation theories. 

Origin of Hot Bubble in NGC 6822 Hubble V Star-Forming Regions

Lee, Hye-In

NGC6822 is an irregular galaxy whose star-forming environment is free of dynamical driving effects. At a distance of ~500 kpc, we can spatially resolve molecular clouds or star-forming regions clearly down to parsec scales. Some of the bright HII regions of NGC6822 have bubbles produced by supernova. We observed the bright HII complex in NGC6822 Hubble V, using an infrared spectrometer, IGRINS, attached on the 2.7 m telescope at the McDonald Observatory. We performed a slit scan mapping of 15" × 7" region (35 × 17 pc) in H and K bands with a spectral resolving power of 45,000. Emission lines of Br? ?2.1661 µm and He? ?2.0587 µm from ionized regions were detected. Additional obtained lines are molecular hydrogen lines of 1-0 S(1) ?2.1218 µm, 2-1 S(1) ?2.2477 µm, and 1-0 S(0) ?2.2227 µm from photo-dissociation regions (PDRs). We show three-dimensional maps of the emission lines and discuss a hot bubble scenario with an expanding ionized shell structure around the central stellar cluster.

Dynamical resonance and the core-cusp problem in dark matter halos

Mori, Masao

We have studied the dynamical response of dark matter (DM) halos in darf galaxies to recurring changes in the gravitational potential of the interstellar gas near the centers of the DM halos. A resonance model between the DM particles and density waves excited by the oscillating external potential is proposed to understand the physical  mechanism of the cusp–core transition of DM halos. We determine that the collisionless system effectively gains kinetic energy from the energy transfer driven by the resonance between the DM particles and the density waves induced by the oscillation of the gravitational potential of the interstellar gas. The condition for the cusp–core transition is such that the oscillation period of the baryon potential is the same as the local dynamical time. The core radius of the DM halo after the cusp–core transition driven by the resonance is shown using the conventional mass density profile of DM halos, which is predicted by the cosmological structure formation models. Moreover, we verify our analytical model by using numerical simulations, whose results validate our resonance model. Therefore, we conclude that the energy interchange between the DM particles and the oscillation of the baryon potential driven by the resonance mechanism plays a key role in solving the core–cusp problem of DM halos.

Galaxy Transformation from Flyby Encounters

Davis, Christina

Galaxy flybys are transient encounters where two halos interpenetrate and later detach. Although these encounters are surprisingly common, their dynamical effects have been largely ignored. Here, we study demographics of flybys within the Illustris Simulation to find out how common these interactions are at various halo mass ranges, and examine their dynamical properties. To characterize changes made by the flybys on the halo or the inner galaxy, we measure changes in structural properties after the encounter. Using a machine learning approach, we find which dynamical properties are important for predicting the changes in the observables.  

Population gradients in dwarf spheroidal galaxies KKs 3 and ESO 269-66

Sharina, Margarita

We compare the properties of stellar populations for globular clusters and field stars in two dwarf spheroidal galaxies (dSphs): ESO 269-66, a close neighbor of the giant S0 NGC 5128, and KKs 3, one of the few truly isolated dSphs within 10~Mpc. The star formation histories of the galaxies are known from the results of the deep stellar photometry of Hubble Space Telescope (HST) images performed in previous studies. The age and metallicity for nuclear star clusters in KKs~3 and ESO~269-66 are known from literature spectroscopic studies: T=12.6~Gyr, [FeH]=-1.5 and -1.55 dex. We analyze the surface density profiles of low and high metallicity (blue and red) stars in KKs3 and ESO 269-66 using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favor of the metallicity and age gradients in the galaxies; 2) globular clusters in KKs 3 and ESO 269-66 contain approximately 4 and 40 percent of all stars with  [FeH]~-1.5- -1.6 dex and the age of 12-14 Gyr, correspondingly. Therefore, globular clusters are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO 269-66, probably thanks to its isolation.

Galactic forces rule dynamics of Milky Way dwarf galaxies

Hammer, Francois

Dwarf galaxies populating the Galactic halo are assumed to host the largest fractions of dark matter,as calculated from their velocity dispersions. Their major axes are preferentially aligned with the VastPolar Structure (VPOS) that is perpendicular to the Galactic disk, and we find their velocity gradientsaligned as well. It suggests that tidal forces exerted by the Milky Way are distorting dwarf galaxies.Here we demonstrate on the basis of the impulse approximation that the Galactic gravitational accelerationinduces the dwarf line-of-sight velocity dispersion, which is also evidenced by strong dependencesbetween both quantities. Since this result is valid for any dwarf mass value, it implies that dark matterestimate in Milky Way dwarfs cannot be deduced from the product of their radius by the square oftheir line-of-sight velocity dispersion. This questions the high dark-matter fractions reported for theseevanescent systems, and the universally adopted total-to-stellar mass relationship in the dwarf regime.It suggests that many dwarfs are at their first passage and are dissolving into the Galactic halo. Itopens a promising way to estimate the Milky Way total mass profile at large distances.

Building the detailed rotation maps of the LMC featured in Gaia Data Release 2

Vitorino da Silva, André Filipe

While the rotation in proper motion of the Large Magellanic Cloud (LMC) has been observationally established for two decades, studies have been based in up to a few tens of stars, only allowing to envisage the global direction and speed of rotation.Gaia Data Release 2 (DR2) has delivered parallaxes and proper motions for more than 1.3 billion sources.  The roughly 24 million of these sources in the direction of the LMC have allowed to create maps showing with great detail the rotation field of the LMC. These maps have been highlighted in the European Space Agency (ESA) web pages and DR2 press releases. Their fingerprint appearance has captured popular interest, having featured in many traditional and web media.In this poster, we discuss the data selection criteria and present the data treatment and visualisation techniques used for creating the rotation maps of the LMC.

The SAGA Survey for Satellites around Analogs of the Milky Way Galaxy: Satellite Properties

Weiner, Benjamin

Dwarf satellite populations are key to understanding the early stages of galaxy formation and the assembly of the stellar halo.  However, models based on N-body simulations often predict more Milky Way satellites than observed, and predictions for satellite velocity dispersions (hence masses) also disagree with the data.  Critically, most satellite studies are based on the Milky Way and M31 systems, and we do not know if these are representative or how satellite systems depend on formation history. The SAGA project aims to measure the distribution of satellite galaxies around a large number of systems analogous to the Milky Way, down to the luminosity of the Leo I dwarf galaxy (M_r< -12), to determine whether the MW and M31 are typical, and to measure the variance in satellite systems between different host galaxies.  We have published complete, spectroscopically confirmed satellite galaxy luminosity functions for the satellite systems around eight Milky Way-like host galaxies, after taking spectra of thousands of candidate objects (Geha et al 2017).  Surprisingly, the majority (26/27) of our satellites are star-forming, as compared to 2 of 5 star-forming Milky Way satellites in the same luminosity range. I will update the progress of the SAGA survey, including spectroscopy of satellite systems around more hosts, and discuss the properties of the satellites we find, in particular their star formation rates and metallicities. The SFRs and mass-metallicity relations may offer probes of the processes affecting satellites after accretion into the host halo.

The HI Neighborhoods Around STARBIRDS

Johnson, Megan

Starbursts are finite periods of intense star formation (SF) thatcan dramatically impact the evolutionary state of a galaxy.Recently, published results have redefined both the duration and spatialextent of starbursts in dwarf galaxies to be longer and more distributedthan previously thought, with star formation efficiencies (SFEs) comparableto spiral galaxies.  The contrast between these SFEs and those typical ofnon-bursting dwarfs highlights the inconsistencies between two SF modes thatcan operate in low-mass galaxies.  These inconsistencies might beexplainable if the starburst mode of SF is externally triggered bygravitational interactions with other nearby systems.  We present new,sensitive neutral hydrogen observations of 18 starburst dwarf galaxies,which are part of the STARburst IRregular Dwarf Survey (STARBIRDS) and eachwere mapped with the Green Bank Telescope (GBT) and/or Parkes Telescope inorder to study the low surface brightness gas distributions, a common tracer for tidal interactions.

RR Lyrae Stars in the Ultra-Faint Dwarf Galaxies in the Southern Sky

Sung, Eon-Chang

We report the first detection of RR Lyrae variable stars in the Crater II dwarf galaxy, a recently discovered ultra-faint satellite of the Milky Way. Based on B, V time series photometry obtained with the Korea Microlensing Telescope Network (KMTNet) at CTIO, Chile, covering about a 3×3 degree field around Crater II, we have identified ~83 fundamental-mode (ab-type) and ~11 first-overtone (c-type) RR Lyrae stars by adopting template light-curve fitting method. Our preliminary analysis suggests an Oosterhoff-intermediate classification of this galaxy from the mean period of the RRab stars, <pab> ≃0.631 days, and the location of them on the period-amplitude diagram. We also estimated the mean metallicity, ⟨[Fe/H]⟩RRab = −1.65 ± 0.15, reddening, ⟨E(B − V )⟩RRab = 0.05 ± 0.02, and distance of Crater II, (m − M)0 = 20.25 ± 0.10 and d⊙ = 112 ± 5 kpc, from the pulsation properties and the mean apparent magnitude, ⟨VRR⟩ = 20.95±0.01, of the RR Lyrae stars. The stellar population model we have constructed indicates that Crater II is dominated by an old population of ∼10.5 Gyr, but is relatively younger than the oldest globular clusters in the MW in good agreement with its red HB morphology compared to the low metallicity. We will discuss the properties of the RR Lyare stars in other southern ultra-faint dwarf galaxies.</pab>

Enabling HST UV Exploration of Dwarf Galaxies and the Low Surface Brightness Universe

Lee, Janice

We present a HST pilot program to broadly enable high-resolution UV exploration of star formation at low densities in nearby galaxies using a strategy to increase observing efficiency by up to a factor of two.  The increased efficiency makes more tractable programs which require several tens to hundreds of orbits to aggregate sufficient numbers of resolved massive stars, young star clusters, and clumps to build statistical samples.  We aim to enable basic characterization of the ensemble properties of star formation in the low density regime in its primary units.  We will discuss first results based on the nearby dwarf galaxy Holmberg I.

XXX IAU General Assembly | ACV - Austria Center Vienna  | Bruno-Kreisky-Platz 1  | 1220 Vienna