Focus Meeting 7 - Abstracts
Galactic archaeology: understanding the metallicity gradients with chemo-dynamical models
Minchev, Ivan
Metallicity gradients seen today in the interstellar medium (ISM) and stellar component of disk galaxies are the result of the entire chemo-dynamical evolution since the beginning of disk formation. In a pioneering paper, Matteucci & Francois (1989) have established that the observed negative Milky Way disk metallicity gradient results from an inside-out disk formation. That the Milky Way has formed inside-out is now evident from the more centrally concentrated older stellar populations, also seen in external galaxies. Knowledge of the ISM metallicity gradient evolution with cosmic time is very important, as it can be related to the SFR and gas properties throughout the galaxy lifetime. I will discuss the abundance gradient evolution of groups of stars with similar age (or mono-age populations) in galaxy formation simulations. It will be shown that gradient inversion with distance from the disk midplane seen in both Milky Way data and simulations results from the mixture of stars with different ages, disk flaring, and inside-out disk formation. Finally, I will present a novel technique for constraining the evolution of the Galactic ISM metallicity with radius and time directly from the observations, while at the same time recovering the birth radii of any stellar sample with good metallicity and age measurements.
Metallicity gradients and evolution based on the LAMOST spectroscopic surveys
Xiang, Maosheng
Stellar metallicity gradients, especially their temporal evolution, set important constrains on the galactic chemical and dynamical evolution history. The LAMOST Galactic spectroscopic surveys have collected 10 million stellar spectra, from which accurate and precise stellar atmospheric parameters, chemical abundance, radial velocity, luminosity (distance) and especially age have been delivered for millions of stars with simple selection function. This unprecedented dataset allows us to characterize the stellar metallicity distributions at different positions and for different ages in great detail, thus to obtain deep insights on the chemical (and dynamical) evolution history of our Milky Way galaxy. In this talk, I will present efforts on characterizing Galactic stellar metallicity gradients and distributions for mono-age populations with LAMOST data, and discuss their constrains on Galactic assemblage and evolution history.
CHemical Abundances Of Spirals: Understanding Gas Content and ISM Conditions through CHAOS
Berg, Danielle
Accurate and robust measurements of extragalactic metallicities are essential to constrain models of chemical enrichment, chemical evolution, and the cycle of baryons in the cosmos. Despite this strong dependence on chemical abundances, an absolute calibration of gas-phase abundances from nebular emission lines has not been definitively established. The CHemical Abundances of Spirals (CHAOS) project leverages the combined power of the Large Binocular Telescope (LBT) with the broad spectral range and sensitivity of the Multi-Object Double Spectrographs (MODS) to uniformly measure ``direct" abundances in large samples of HII regions in spiral galaxies. Thus far, CHAOS has increased, by more than an order-of-magnitude, the number of H II regions with high-quality spectrophotometry to facilitate the first detailed measurements of the chemical abundances of a statistically significant sample of nearby disk galaxies. These observations, which include a large number of low excitation H II regions, have led to several unexpected results, challenging our current understanding of the trends in gas conditions, ionization correction factors, relative abundances, and more. Fortunately, the unprecendented number of sensitive diagnostics in the rich CHAOS dataset allows for new approaches to investigate these issues. In addition to helping us understand nearby galaxies, calibrating the nebular abundances of massive galaxies has important implications for deciphering the ISM in more distant galaxies and properly calibrating the spatially resolved abundances from IFU surveys.
An overview on radial metallicity gradients with Galactic nebular tracers
García-Rojas, Jorge
I will present a review on the last determinations of radial abundance gradients obtained from the analysis of HII regions and planetary nebulae deep spectrophotometric data in our Galaxy. Comparison between planetary nebulae and HII regions gradients have been usually done as a check of the time evolution of the metallicity gradient. However, I will put the eye on some problems that should be carefully addressed. Additionally, I will not focus only on metallicity indicators (as Oxygen) but also in other interesting elements as Nitrogen, Carbon, and alpha-elements trying to emphasize the importance of precise determinations of the gradients of these elements on the understanding of the nucleosynthetic origin of the elements and on the chemical evolution of our Galaxy.
Metallicity gradients in the nearby Universe: shedding new light on the role of gas flows in galaxies with MaNGA
Belfiore, Francesco
Theoretical models demonstrate that galaxy evolution is largely shaped by the interplay between inflows, star formation and feedback processes. Since chemical abundances are sensitive to the integrated effect of gas flows and star formation, they constitute the ideal tool to improve our understanding of these phenomena. I will present a new study of metallicity gradients in the low-redshift Universe from SDSS-IV MaNGA, the largest integral field spectroscopy survey of nearby galaxies to date. The observed dependence of the metallicity gradient on stellar mass will be discussed in the context of an updated 'bath-tub' model, which we have developed to extend the previous model formalism to resolved scales in galaxies. In particular, I will focus on the importance of including inside-out growth in the models, and on the relation between metallicity profiles and other observables (e.g. SFR, stellar mass). Intriguingly, our results confirm the presence of a statistically significant flattening of the metallicity gradient at large radii. I will conclude discussing the possible implications of this result for our understanding of gas flows and recycling in galaxies.
Dust gradients and solid-phase metallicity
Bianchi, Simone
The recent Herschel mission has allowed to study the distribution of cold dust in nearby galaxies with unprecedented resolution. Radial gradients in the dust mass have been found to be flatter than the stellar, and intermediate between those of the molecular and gas components. In principle, dust and gas resolved observations can be used together to derive the metallicity gradient in the solid phase. There are however several potential pitfalls: dust properties might vary with the environment, and thus bias the mass estimates over that predicted using grain models for the diffuse MW ISM; the shape of the SED - and again the mass estimate - might depend on an uncertain local inter-stellar radiation field; also, the solid-phase metallicity depends on uncertain, metallicity and environment dependent, conversion factors to obtain the total molecular gas from observations of CO. Nevertheless, a number of attempts have been made to derive the dust properties, dust-to-gas ratio and CO-to-H2 conversion factors from far-infrared observations. I will report on these studies, focusing on the results from DustPedia, a database of almost all resolved galaxies in the local Universe observed by Herschel.
The impact of the APOGEE Survey on Galactic metallicity gradients
Bovy, Jo
Determining the structure of the Milky Way is one of the oldest problems in astronomy and yet it still has surprises in store. A new generation of surveys is expanding our high-resolution view of stellar populations in the Milky Way from a small region around the Sun to the entire radial range of the stellar disk. I will present new results on the global chemical and spatial structure of the disk from the APOGEE survey. These results challenge long-held assumptions about the basic structure of galactic disks, the importance of mergers for their evolution, and the physical conditions under which stars form throughout cosmic time.
Metallicity gradients and galaxy formation.
Tissera, Patricia
The chemical abundances of the gas-phase and stellar components of galaxies are key importance to undertand galaxy formation and evolution.It has been shown that an inside-out disc formation yield negative chemical profiles globally. However, a large spread in metallicity gradients has been reported by recent and more precise observations,suggesting the action of other physics processes such as gas outflows and inflows, radial migration, andmergers and interactions.Cosmological simulations including chemical models provide a tools to tackle the origin of the metallicityprofiles and the action of those processes which might affect them as a function of time.In this talk I present a summary of the current state-of-knowledge from a numerical point of view and discuss the main results from the analysis of the EAGLE simulations.
Emission-line diagnostics for metallicity gradients in galaxies
Kewley, Lisa
I will present an overview of the application of emission-line diagnostics for diagnosing the metallicity gradients in galaxies. I will summarize the current state-of-the art in metallicity diagnostics, including empirical, theoretical, and Bayesian statistical methods for calculating metallicities across galaxies. I will describe what we have learned and what still can be learned from metallicity gradients in isolated and merging galaxies using integral field spectroscopic surveys, including chemical evolution, the impact of gas inflows, galactic-scale outflows, metallicity gradients in AGN, and tidal effects on metallicity gradients during galaxy mergers. I will conclude with a simulation of how metallicity gradients can be measured in the future on the ELTs.
Radial metallicity gradients with Galactic stellar probes
Inno, Laura
By being the only galaxy that we can resolve star-by-star, the Milky Way (MW) is an ideal model organism to test our understanding of galaxy formation and evolution. After their birth, the MW stars change their orbit through secular evolution processes, but not their chemical abundances that encode the composition of their gaseous birth material. As a result, the spatial variation of stellar metallicity in the disk reflects the Galactic assembly history at different radii, providing a key constraint for MW evolution models. In particular, the decreasing of heavy element abundances as a function of Galactocentric radius, i.e. the negative metallicity gradient, is the observable counterpart of the “inside-out” formation of the disk. However, a large diversity of measured gradients can be found in the literature, with values ranging from -0.01 to -0.09 dex/kpc, depending on the tracers used. In order to understand if this diversity comes from Galactic evolution processes or observational biases, stellar probes uniformly distributed across the disk and with accurately known ages are needed. Such tracers have now been made available by large spectroscopic surveys (e.g. Gaia-ESO, APOGEE etc.), which have extensively targeted and characterised selected stellar probes. In this talk, I will review recent results on the metallicity gradients measured for old (Red Giants), intermediate (Open Cluster) and young (Cepheids) stellar probes, and discuss their implication for Galactic evolution. But among these tracers, only Cepheids are luminous enough to be seen even through substantive dust absorption, thus throughout the entire disk. I will present new results based on hidden Cepheids recently discovered in the extremely obscured regions of the disk, which allow us to determine the chemical content of the mixed gas at the interface between the inner Galactic components, and of pristine infalling gas in the flared disk.
Nitrogen isotopic ratio across the Galaxy
Colzi, Laura
The abundance ratio 14N/15N is considered a good indicator of stellar nucleosynthesis since the two elemental isotopes are not originated in the same way. Both isotopes have indeed an important secondary production in the CNO cycles. There is the cold CNO cycle that takes place in main-sequence stars and in the H-burning shells of red giants: 14N is created from 13C or 17O and brought in stellar surfaces through dredge-up on the red giant branch. Furthermore, there is the hot CNO cycle, that occurs instead in novae outbursts and is the main way to produce 15N. However, there is also a strong primary component of 14N created in the so-called Hot Bottom Burning (HBB) of asymptotic giant branch (AGB) stars (e.g. Schmitt & Ness 2002), and an (over-)production of 15N with respect to 14N in the relative role played by massive stars and novae (Romano et al. 2003, 2017). Therefore, 15N is principally a secondary element. These different origins lead to an increase of 14N/15N ratio with the Galactocentric distance, up to 8 kpc, as predicted by models of Galactic chemical evolution (GCE, e.g. Romano et al. 2017). However, the relative importance of these processes is still unclear. The only way to test these theoretical predictions is to provide more observational constraints. We report the measurements of the 14N/15N ratio derived in a sample of 87 dense cores that span Galactocentric distances in the range 2–12 kpc, and we present a new Galactocentric behavior of 14N/15N. This is the first time that such a statistically robust sample has been used to study the Nitrogen isotopic ratio across the Galaxy. We are also able to compare this trend with GCE models, and we found some correlations between observations and models (Colzi et al., MNRAS submitted). Moreover, we have also found a new local 14N/15N interstellar medium (ISM) value of about 400, i.e. closer to the PSN (Proto-Solar Nebula) value (about 441, Marty et al. 2010) with respect to past derived value.
Supergiant stars as Cosmic Abundance Probes
Patrick, Lee
Massive stars are important probes of chemical evolution in star-forming galaxies. They represent the brightest stellar components of external galaxies and have been used in recent years to examine the metal-content and -distribution in many Local Universe galaxies out to distances of ~20 Mpc. These measurements probe the youngest stellar population and provide robust, independent estimates of radial abundance gradients, important to constrain models of galactic chemical evolution and to anchor the more uncertain nebular estimates at larger distances. Blue and Red Supergiant stars are the brightest of the stellar population in the optical and near-IR, respectively. Even though these stars are evolved products, they are still remarkably young objects (<50Myr). Using intermediate resolution Multi-object spectroscopy combined with state-of-the-art stellar model atmospheres, I demonstrate how these two unique types of stars can be used to estimate stellar abundances in external galaxies. Recent results demonstrate the internal consistency between these measurements and I will present a comparison with nebular probes in the Local Universe. By compiling results from red and blue supergiants, I will present the Mass-Metallicity relation as derived from different stellar tracers and demonstrate the excellent agreement between these probes. By comparing this result with nebular measurements we determine that those empirically calibrated to direct-method studies provide the most consistent results.
A systematic study on isotope ratios toward molecular clouds in our Galaxy
Zhang, Jiangshui
Isotope abundance ratios play a key role in our understanding of stellar nucleosynthesis, stellar ejecta, and the chemical evolution of the Milky Way. So far, however, there are a few works on C, O, S isotopes and especially lack data from the Galactic center region and far outer galaxy, no systematic research has been done. Thus we are performing systematic studies on the isotope ratios, including 18O/17O and 12C/13C, 32S/34S, 14N/15N etc. Here we present results on isotopic ratio of 18O/17O toward a large sample of more than 150 sources, including especially many sources with large galactocentric distance. Our observations on C18O and C17O J = 1–0 lines were performed thorough ARO 12m and IRAM30m telescopes. Our preliminary results support a radial gradient along the Galactic disk for the abundance ratio, which is consistent with the inside-out formation scenario of our Galaxy. Our coming J=2-1 line data of C18O and C17O toward our large sample will be important for constraining opacities and abundances and finally confirming the Galactic radial gradient. Our performing observations on other isotope ratio projects will also be introduced.
Oxygen abundance profiles with MUSE: radial gradients and widespread deviations
Sánchez-Menguiano, Laura
In a recent publication (Sánchez-Menguiano et al. 2018, A&A, 609, A119) we characterised the oxygen abundance radial distribution of a sample of 102 spiral galaxies observed with VLT/MUSE for which a total of 14345 H II regions were detected. We developed a new methodology to automatically fit the abundance radial profiles, that are derived using the calibration proposed in Marino et al. 2013 for the O3N2 indicator. We find that 55 galaxies of the sample exhibit a single negative gradient. The remaining 47 galaxies also display, as well as this negative trend, either an inner drop in the abundances (21), an outer flattening (10), or both (16), which suggests that these features are a common property of disc galaxies. The presence and depth of the inner drop depends on the stellar mass of the galaxies with the most massive systems presenting the deepest abundance drops, while there is no such dependence in the case of the outer flattening. We find that the inner drop appears always around 0.5 re, while the position of the outer flattening varies over a wide range of galactocentric distances. Regarding the main negative gradient, we find a characteristic slope in the sample of aO/H = -0.10 ± 0.03 dex /re. This slope is independent of the presence of bars and the density of the environment. However, when inner drops or outer flattenings are detected, slightly steeper gradients are observed. This suggests that radial motions might play an important role in shaping the abundance profiles. We define a new normalisation scale ("the abundance scale length", rO/H) for the radial profiles based on the characteristic abundance gradient, with which all the galaxies show a similar position for the inner drop (0.5 rO/H) and the outer flattening (1.5 rO/H). Finally, we find no significant dependence of the dispersion around the negative gradient with any property of the galaxies, with values compatible with the uncertainties associated with the derivation of the abundances.
Time evolution of the metallicity gradients
Athanassoula, Lia
I will present results from over two dozens high resolution chemodynamical simulations of disc galaxies, including both isolated and merger-related cases. In particular, I will present the radial metallicity gradients for stellar populations at different distances from the equatorial plane and their evolution with time. I will also discuss recent results on the distribution of stars in the [Mg/Fe] versus [Fe/H] plane in my simulations and how this evolves with lookback time. In the same way as for the radial metallicity gradients, I will consider either all disc stars, or only populations from specific radial and vertical bins, as well as age bins. Preliminary comparisons with observations show a good agreement, particular concerning the multi-component signatures. My results allow me to discuss the effect of radial migration on these distributions and radial gradients.
The dust/gas/metallicity scaling relations in the Local Universe
Casasola, Viviana
The mass of the interstellar medium (ISM) is composed of gas for ~99% and primarily of dust for the remaining ~1%. Although the dust constitutes a small percentage of the ISM, understanding its properties is of particular importance for several reasons, including the possibility of using dust as tracer of the chemical evolution of the ISM. Dust is indeed composed by metals, and thus it allows an alternate way to measure metallicity. Metals are produced mainly by the stellar nucleosynthesis and then returned to the ISM, either as gas and as solid grains condensed during the later stages of stellar evolution; they can later be destroyed and incorporated into new generations of stars. This matter cycle (between gas, dust, metals, star formation process) is critical for the study of the formation and evolution of galaxies. I will present the main scaling relations involving molecular, atomic and total gas and dust (and their ratios) as a function of the metallicity for a sample of ~400 nearby, late-type galaxies extracted from the DustPedia sample, a database of almost all resolved nearby galaxies observed by Herschel. Since the DustPedia project is addressing many aspects of the galaxy evolution such as growth of the metal abundance, loss of metals in galactic winds, physical processes in the ISM, studies in the DustPedia context are particularly adapt to characterize metal content with dust.
Precise evolution of metallicity radial gradients at cosmic noon and its constraints on galaxy evolution
Wang, Xin
The chemo-structural evolution of galaxies at the peak epoch of cosmic star formation is a key issue in galaxy evolution physics. To address this, we investigate the spatial distribution of gas-phase metallicity in emission-line galaxies in the redshift range of z~1-3, i.e., at the cosmic noon. In a series of papers, we bring forward a novel method of obtaining sub-kpc resolution metallicity maps using space-based grism spectroscopy of strongly lensed galaxies. The sufficient spatial sampling, achievable only through the synergy of diffraction-limited data and lensing magnification, is crucial to avoid spuriously flat gradient measurements. Combining the deep HST/WFC3 near infrared grism data acquired by the GLASS project and a novel Bayesian method inferring metallicity from line fluxes directly, we obtained over 80 unbiased metallicity maps at z~1.2-2.3. This improves the number of such measurements by one order of magnitude. Our maps reveal diverse galaxy morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, which can effectively affect the gas and metallicity distributions in individual galaxies. We found two sub-luminous galaxies at z~2 displaying greatly inverted gradients, strongly suggesting that powerful galactic winds triggered by central star bursts carry the bulk of the stellar nucleosynthesis yields to the outskirt. We also observe an intriguing correlation between stellar mass and metallicity gradient, consistent with the ``downsizing'' galaxy formation picture and inside-out disk growth. Furthermore, 10% of the gradients measured in our sample are positive (i.e. inverted), which are hard to explain by currently existing hydro-simulations and analytical models. Our techniques can also be applied to data from future space missions employing grism instruments, e.g., JWST, WFIRST, Euclid.
The radial galactic distribution of the ionizing field of radiation in HII regions using photoionization models
Pérez-Montero, Enrique
HII regions in galaxy disks can be used as a powerful tool to trace the radial distribution of several of their properties and shed some light on the different relevant processes on galaxy formation and evolution. Among the properties that can be extracted from the study of the ionized gas are the metallicity, the excitation and the hardness of the ionizing field of radiation. These parameters are usually estimated in un-resolved star-forming complexes from the comparison of the relative fluxes of the most prominent emission-lines with sets of very well characterized data or from photoionization models. In this contribution we will focus on the determination of both the ionization parameter and the effective temperature of the ionizing clusters in those regions with a well derived metal content it is possible to establish a direct comparison between observations and model predictions in the plane of [OII]/[OIII] vs. [SII]/[SIII] to give accurate estimations of these parameters. We will also show the implications that the use of our appropriate Chi square comparison have to the study of the radial variation of both excitation and effective temperature in some very well-studied disk galaxies of the Local Universe and their interplay with metallicity gradients in these objects.
The evolution of the Milky Way's radial metallicity gradient as seen by APOGEE, CoRoT, and Gaia
Anders, Friedrich
The time evolution of the radial metallicity gradient is one of the most important constraints for Milky Way chemical and chemo-dynamical models. In this talk we review the status of the observational debate and present a new measurement of the age dependence of the radial abundance gradients, using combined asteroseismic and spectroscopic observations of 418 red giant stars located close to the Galactic disc plane (6 kpc < RGal < 13 kpc). The radial iron gradient traced by the youngest red-giant population (-0.058 +- 0.008 +- 0.003 dex/kpc) reproduces the results obtained with young Cepheids, while for the 1-4 Gyr population we obtain a slightly steeper gradient (-0.066 +- 0.007 +- 0.002 dex/kpc). For older ages, the gradient flattens again to reach values compatible with zero at around 10 Gyr. We compare our results to state-of-the-art chemo-dynamical Milky Way models and recent literature results obtained with open clusters and planetary nebulae. We will also present first results from APOGEE+Gaia-DR2-derived ages of turn-off stars.
Go beyond radial metallicity gradient: azimuthal variations of oxygen abundance viewed in 3D
Ho, I-Ting
The spatial distribution of the interstellar medium oxygen abundance is the key to understanding how efficiently metals that are synthesized in massive stars can be redistributed across a galaxy. One way to understand how efficient chemical mixing of the ISM occurs on gas orbital timescale is to probe chemical inhomogeneity in the azimuthal direction. Despite decades of studies, evidence of the presence of azimuthal variations of chemical abundances remains circumstantial, in sharp contrast to the copious observational efforts in probing radial gradients. In this talk, I will present two case studies of nearby (<20Mpc) galaxies observed with the TYPHOON Program that delivers 3D optical data with about 100 pc physical resolution and full disk areal coverage. I will show compelling evidence that the ISM oxygen abundance changes systematically in the azimuthal direction. The abundance variations spatially correlate with the spiral structures and are imprinted on negative radial gradients. I will place the observations in the framework of a simple chemical evolution model. I will demonstrate that the systematic, periodic variations are caused by the competition of two physical processes, localized, sub-kpc-scale self-enrichment and efficient, kiloparsec-scale mixing-induced dilution driven by spiral density waves. I will end the talk by discussing future prospects of using the on-going MUSE and ALMA large programs by the PHANGS collaboration to advance our understanding of chemical abundances and mixing on sub-kiloparsec scale.
Metallicity gradients in M31, M33, NGC 300, and Milky Way using Argon abundances.
Flores Duran, Sheila Nathanya
It has recently been shown that oxygen in Planetary Nebulae (PNe) may be enriched in low-metallicity environments (Peña et al. 2007; Flores-Durán et al. 2017) and also in Galactic planetary nebulae with carbon-rich dust (Delgado-Inglada et al. 2015). Therefore metallicity gradients derived from oxygen abundances in PNe could be modified by stellar nucleosynthesis and then this gradient is not adequated to analyse the chemical evolution of galaxies. Apparently neon abundances are also modified by stellar nucleosynthesis (Karakas 2010) but argon abundandances in PNe are not modified in such processes during the PNe progenitor lifetime. Hence we propose to use argon to trace the metallicity gradients in the galaxies of the local universe M31, M33, NGC 300, and the Milky Way. We will show the PNe argon gradients in comparison with H II regions.ReferencesDelgado-Inglada, G., Rodríguez, M., Peimbert, M., Stasinska, G. & Morisset, C.2015, MNRAS, 449, 1797Flores-Durán, S. N., Peña, & Ruiz, M. 2017, A&A, 601, 147Karakas, A. I. 2010, MNRAS, 403, 1413Peña, M., Stasinska, G., & Richer, M. G. 2007, A&A, 476, 745
The Klever Survey: spatially resolved metallicity maps and gradients in high redshift galaxies
Curti, Mirko
We will present the first results from KLEVER, an ESO Large Programme aimed at investigating dynamics, gas excitation properties and chemical abundances in high redshift galaxies, by means of near-IR spatially resolved spectroscopy. Exploiting KMOS multi-IFU observations in the J,H and K bands we aim to map multiple optical rest-frame nebular diagnostics (from [O II]3727 to [S III]9530) in a sample of ~150 galaxies between 1.2 < z < 2.5, allowing a full, detailed characterisation of the properties and excitation mechanism of the ISM in these objects on a spatially resolved basis. Here we discuss the results of the analysis of the first available observations, mostly targeting lensed galaxies in CLASH and Frontier Fields clusters.Thanks to the broad set of emission lines provided by the survey, we infer the chemical abundances in our sample exploiting a variety of different diagnostics and compare the predictions from different calibrations. We derive spatially resolved, source-plane metallicity maps and extract radial gradients to assess shape, correlation with different galaxy properties and evolution with cosmic time.The bulk of the galaxies analysed so far are characterized by azimuthally averaged radial metallicity gradients fully consistent with being flat; this may support a scenario in which efficient mixing processes, that redistribute a significant amount of gas over large scales, are in place at these epochs.However, the presence of irregular and asymmetric patterns, as seen in many of the full 2D metallicity maps, warns against the use of radial gradients as the only observable to constrain galaxy evolution models and simulations. A new, physically and statistically meaningful approach to extract information from the metallicity maps beyond the radial averages is explored, tested on KLEVER data and discussed also in light of forthcoming facilities (e.g. JWST).
Chemical Evolution of the Milky Way Disk: Insights from the TGAS-RAVE-LAMOST Dataset
Vickers, John J
We study the enrichment of 125,000 stars in a spectroscopic-photometric dataset (TGAS, LAMOST, RAVE) as a function of their dynamics and inferred ages. The dynamics can be used to estimate birth radii (if heating is the main influence, and not large-scale migration), which, when coupled with age and abundance information, can describe the enrichment rates at different radii in the disk. Using such an analysis, we find that, while the disk interior to the Sun enriched first, the outer disk is currently enriching more quickly. By considering the enrichment profile of the Milky Way ISM along with the dynamics of stars, we can select a small sample which are more metal rich than the ISM at their current orbital radii, this is indicative of these objects having migrated from interior regions of the galaxy. Adding in our age information, we find these objects to be disproportionately young, which is consistent with the idea of potential-driven migration primarily affecting dynamically cooler (younger) populations.
Resolving gas-phase metallicity gradients of intermediate redshift galaxies with MUSE
Carton, David
We present results from a systematic study on the metallicity properties of 84 intermediate redshift galaxies (0.1 < z < 0.8) using data from the MUSE Guaranteed Time Observing programme. With the MUSE GTO programme we are targeting galaxies across the field and group environments, observing more than 10 fields to a minimum depth of 10h each. In particular we shall present results on the gas-phase metallicity gradients of galaxies in these fields. Metallicity has proven to be an especially interesting probe of galaxy evolution because it traces the effects of gas accretion and wind-driven outflows. However, owing to the limitations of seeing, little is known to date about the resolved metallicity properties of intermediate redshift galaxies. To investigate these barely resolved objects we have developed a forward modelling technique that allows us to correct for the effects of seeing upon the observed metallicity gradient. Using this we find, contrary to other higher redshift studies, that once the star-formation rate is normalized relative to the main sequence, there is no correlation between the star-formation intensity and the metallicity gradient. In addition, we find only a few galaxies (7 out of the 84) with positive metallicity gradients (centres more metal-poor than their outskirts). We note that, while for the smallest galaxies in our sample there is a large spread in the observed metallicity gradients (both negative and positive), we find no large galaxies (rd > 3 kpc) with positive metallicity gradients. Altogether this is suggestive of a secular evolutionary scenario, with the largest (most well-evolved) galaxies been analogous to present-day galaxies, which also show a common negative metallicity gradient.
Metallicity gradients in absorption-selected intermediate-redshift galaxies
Christensen, Lise
Strong absorption lines in quasar spectra arise when the lines of sight to distant quasars intersect intervening galaxies. Associated metal absorption lines from the strongest hydrogen absorption lines, the damped Lyman alpha absorbers (DLAs), allow us to trace accurate metallicities of galaxies back to redshifts z>5. This has revealedmetallicities typically around 0.1-100% solar values with a gradual increase in metallicity with increasing cosmic time as expected when DLAs get enriched from star-formation processes. DLAs have metallicity distributions roughly similar to that of Milky Way halo stars, but with a large spread in the range of metallicities.In order to understand the connection between the DLAs and the host galaxies and how the metallicities vary with radial distances, we first need to detect the host galaxy in emission. This search has evolved rapidly in past decade, and we now have a sufficiently large sample of more than a dozen absorber-galaxy pairs out to redshifts z>2, where we can compare metallicities in emission and absorption.I will present resent results and explain how we have determined metallicity gradients in circumgalactic environment of the galaxies out to ~40 kpc at intermediate to high redshifts. In addition to deriving gradients, these values allow us to reproduce observed galaxy scaling relations, such as the mass-metallicity relation, observed in conventional luminosity-selected galaxy samples. This suggests that the origin of metallicity gradients seen in local disk galaxies arise at higher redshifts, and can be probed by absorption line spectroscopy.
What the Milky Way bulge reveals about the initial metallicity gradients in the disc
Fragkoudi, Francesca
We explore the origin of metallicity gradients in the Milky Way (MW) bulge with two N-body models of disc galaxies which form a bar and a boxy/peanut (b/p) bulge, and compare their predictions to APOGEE data. The first model is a composite disc, made up of thin and thick disc stellar populations, where the metal-poor and alpha-enhanced thick disc populations contribute significantly to the inner disc stellar mass budget. The second model is a single disc with an initial steep radial metallicity gradient. While the latter model reproduces the vertical metallicity gradient seen in the MW bulge, it does not reproduce other observed trends in metallicity, as seen with APOGEE data. On the other hand, the composite disc model naturally reproduces all the observed trends. We therefore see that it is possible to reconcile a (primarily) disc origin of the MW bulge with the observed trends in metallicity of the inner MW. These findings also point to an almost flat radial metallicity gradient in the inner disc of the MW, before bar and b/p bulge formation.
Gas and stellar metallicity gradients in face-on disk galaxies
Sanchez-Blazquez, Patricia
I will present an analysis of the metallicity gradients in a sample of 200 disk galaxies from the CALIFA survey. The metallicity gradient of both the stellar and the gas-phase component will be compared as well as their correlation with other parameters, like mass, morphological type, presence of bar, type of spiral arms and gas fraction. I will also present the correlations with both, the age and [Mg/Fe] gradients for the stellar components. This analysis allow us to conclude about the evolution of the metallicity gradients with time as well as the influence of axysymmetric features in producing radial migration.
Radial elemental abundance gradients in galaxies from cosmological chemodynamical simulations
Vincenzo, Fiorenzo
Radial chemical abundance gradients in galaxies can retain fundamental information about the galaxy growth as a function of time, as well as about the interaction of the galaxy with its surrounding environment. Cosmological chemodynamical simulations can be very useful tools in this respect, because the effects of inside-out growth, stellar migrations, and galaxy mergers can be, in principle, disentangled. In the first part, I will present the results of our study for a sample of star forming galaxies with different star formation histories in our cosmological chemodynamical simulation. We can reproduce with our simulation the global observed mass-metallicity relation, the observed cosmic star formation rate, and the N/O versus O/H chemical abundance pattern as observed in nearby galaxies. I will show our predictions for the redshift evolution of the radial chemical abundance gradients both in the gas and in the stellar populations of our simulated galaxies. In the second part, I will show results from zoom-in chemodynamical simulations, where a target galaxy is selected at low redshift from a full cosmological simulation and then re-simulated with a larger number of resolution elements, starting from the initial conditions of the early Universe.
Exploring the taxomony of metallicity gradients in SDSS-IV MaNGA interacting galaxies
Barrera-Ballesteros, Jorge K.
Observational evidence suggests that for a non-interacting star-forming galaxy, the radial distribution of the gas metallicity follows a negative gradient supporting the inside-out galactic evolution scenario. On the other hand, due to tidal-induced radial movements towards galactocentric regions, interactions and mergers have been advocate to flatten the observed negative gradient in isolated galaxies. The lack of a large sample with spatially resolved maps of metallicity has hampered the study of the statistical impact of mergers in metallicity gradients. In this study we present the gas-phase metallicity radial distribution derived in more than 500 interacting galaxies included in the Integral-Field Unit (IFU) SDSS-IV MaNGA survey. Thanks to the large IFU MaNGA sample, we are able to compare these gradients with more than 3000 non-interacting control galaxies. We explore the variety of shapes observed in the metallicity gradients for interacting galaxies as well as quantify the impact of global parameters.
The relevance of the Gaia-ESO survey on the Galactic metallicity gradient
Randich, Sofia
The Gaia-ESO Survey has observed more than 100,000 stars belonging to different Galactic populations, including about 65 open star clusters that well sample the age - Galactocentric distance parameter space. This homogeneous dataset is enabling a detailed determination of the metallicity gradient and its time evolution. I will present recent results from the latest Gaia-ESO internal data release, with particular emphasis on the open clusters, and will show how these allow new and challengig observational constraints to be put on the models.
The relation of the oxygen abundance radial gradient in spiral galaxies with the formation process of their disks
Molla, Mercedes
We analyse the evolution of the oxygen abundance radial gradient for galaxies of different total masses and different star formation efficiencies and the correlations of these gradients with stellar mass, effective radius or morphological type. Our main result is that the radial gradient shows a strong variation only in the very early time when stars start to form in regions out of the centre of galaxies. Then, once the disk appears, the evolution is very smooth along the time or redshift. We compare our predictions with a set of existing data showing good agreement with the negative radial gradients, while the positive gradients can not be explained with our models for isolated galaxies. We interpret the positive radial gradients observed at high redshift as corresponding to galaxies in interaction. We also compare with cosmological simulations showing good agreement with the most recent results.