Focus Meeting 6 - Abstracts
EXPANDING ANGULAR MOMENTUM MEASUREMENTS TO DWARF GALAXIES
Chengalur, Jayaram
We use high-resolution HI observations and broad band photometry to measure the baryonic mass (Mb) and baryonic specific angular momentum (jb) for dwarf irregular galaxies in different environments. We find that for dwarf galaxies jb scales approximately linearly with Mb. This is similar to what is observed for larger bulgeless spirals. We also find that the jb-Mb relation for dwarfs does not have a measurable dependence on the large scale environment, with dwarf galaxies in voids showing similar trends to dwarf galaxies in fields and the outskirts of small groups. However, all dwarf irregular galaxies, regardless of the large scale environment have significantly higher specific angular momentum than expected from the relation obtained for bulgeless spiral galaxies. We combine our data with data from earlier studies and find that this increase in specific angular momentum occurs for dwarf galaxies with masses lower than 109.1 Interestingly, the mass threshold that we find, viz, 109.1 Msun is very similar to the mass threshold below which galaxy discs start to become systematically thicker. The approximately linear trend between jb and Mb that we find in the dwarf galaxies is qualitatively consistent with models in the bulk of the baryonic matter in the disk is in the form of a gas disk which is marginally stable as per the Toomre criteria. In such models feedback from centrally concentrated star formation could preferentially remove the low angular momentum gas from the central parts of dwarfs (and so increase the specific angular momentum of the remaining material) and also inject mechanical energy, leading to thicker discs. We find however, that the observed amount of star formation in our sample galaxies is insufficient to produce the measured increase in the specific angular momentum. It hence appears that some other, as of yet not identified mechanism, plays a role in producing the observed enhancement in specific angular momentum.
Galaxy simulations after the angular momentum catastrophe
Obreja, Aura
Numerical studies of the non-linear problem of galaxy formation in a hierarchical universe have now ~30 years of history behind. However, for half of this timespan, galaxy simulations suffered from the so-called "catastrophic loss of angular momentum", resulting in too small and compact galaxies as compared to the observed Universe. This problem largely got solved by improving the numerical algorithms, increasing the resolution and taking into account baryonic feedback processes affecting the gas accretion, cooling and angular momentum transport. Nowadays cosmological simulations of galaxies are resembling the observed Universe, and therefore provide a new means to probe and study in a quantitative manner the origin and evolution of galaxy angular momentum. We use 25 simulated objects from the NIHAO sample to define and characterize a variety of stellar kinematic structures in galaxies: thin and thick discs, large scale single discs, classical and pseudo bulges, spheroids, inner discs, and stellar haloes. These structures have masses, spins, sizes, shapes and rotational support in good agreement with theoretical expectations based on observational data. Above a dark matter halo mass of 11.4 dex, all galaxies have a classical bulge and 70 per cent of them have a thin and thick discs. By tracing back in time the progenitors of all these structures it is possible to constrain their formation history. We find that all types of stellar structures lose a fraction of their maximum angular momentum, acquired at early times from the tidal torques. Surprisingly, even structures like single large scale discs or thin discs can lose an important part of their maximum spin (up to ~70 per cent), and still fulfill the redshift 0 properties of cold discs. We also find that the observed maximum rotational velocity and angular momentum of the cold stellar discs are tightly correlated with the total dynamical mass of the galaxy and the spin of the inner dark matter halo.
Emerging angular momentum physics from kinematic surveys
Colless, Matthew
I will review the insights emerging from recent kinematic surveys of galaxies, with particular reference to the SAMI survey on the Anglo-Australian Telescope. These new observations provide a more comprehensive picture of the angular momentum properties of galaxies over wide ranges in mass, morphology and environment. I will focus on the distribution of angular momentum within galaxies of various types and the relationship between mass, morphology and specific angular momentum. I will discuss the implications of the new results for models of galaxy assembly.
"The fundamental physics of AM evolution in a LCDM scenario"
Pedrosa, Susana
Galaxy formation in the current cosmological paradigm is a complex process where several physical mechanisms like inflows, outlfows, interactions and mergers take place and that shape the galaxy. These processes can redistribute the angular momentum content of baryons. Observational results suggest that discs formed conserving angular momentum while elliptical galaxies end up losing a great fraction of it. But the underlining mechanism acting during the assembly of the galaxy still needs to be understood.Using cosmological hydrodynamical simulations that include an effective, physically-motivated Supernova feedback, we perform a thorough study of the components of the galaxies, their interplay and their progenitor systems.
Angular momentum transport in lopsided galaxies
Saha, KANAK
More than a third of spiral galaxies in the local universe are known to host large-scale lopsidedness. Such lopsided asymmetries are observed both in stars and gas, and are, in general, prominent in the outer parts of a galaxy. The role of such asymmetry in the dynamical evolution of a galaxy has been little explored so far. Following Lynden-Bell's approach, we compute the transport of angular momentum in the combined stars and gas disk embedded in a dark matter halo. It is shown that the lopsided asymmetry can participate in flowing angular momentum outwards provided it is leading in nature. We discuss how the angular momentum transport due to lopsidedness and spiral arms can facilitate inflow of gas from outside and thereby play an useful role in galaxy evolution.
The gravitational origin of angular momentum – reflections on the history and present situation
Peebles, James
The gravitational theory gained favor from two developments. Numerical N-body simulations pretty convincingly showed that the analytic estimate of the spin parameter is about right. And the realization that galaxies likely are dominated by non-dissipative dark matter meant the luminous parts would have to have dissipatively settled to dominate the central parts of galaxies, in the process spinning up the rotation acquired by gravity to support discs. The alternative picture at the time was that spiral galaxies are fossil eddies from primeval turbulence. But in general relativity turbulence could not have lasted long after decoupling. This is not a criticism: healthy progress in science is capricious. But I wonder whether we are again ignoring inconvenient evidence. I shall seek opinions on whether large spirals with inconspicuous classical bulges, which are quite common nearby, challenge standard ideas about how the galaxies formed.
Modelling the cosmic evolution and large-scale alignment of angular momentum
Dubois, Yohan
Galaxies get angular momentum by cosmic gas infall from large-scale filaments. While merger-free disc galaxies should directly inherit from this gas infall, massive elliptical galaxies, for which most of the mass is assembled through mergers, obtain angular momentum differently than from smooth gas accretion. Those two different pictures of angular momentum acquisition lead to two significantly different signals of galaxy alignments in the cosmic web for discs and elliptical galaxies. I will show results from Horizon-AGN, a high-resolution hydrodynamical cosmological simulation, on galaxy alignments and the role played by feedback from active galactic nuclei in settling i) the change of morphology in massive galaxies, and ii) the reorientation of their angular momentum.
Observing various alignment signals of galaxies
Yang, Xiaohu
In this talk, I will present some recent observational measurements of various alignments of galaxies with respect to the orientations of the brightest central galaxies (BCG), the cosmic web structures, etc. These alignments are measured for the distributions of galaxies, the orientations of the galaxy major axes, spin axes, etc. The main findings in these measurements include: (1) satellite galaxies are preferentially distributed along the major axes of the BCGs, (2) the red satellites are preferentially aligned radially with the direction to the BCGs, (3) the major axes of galaxies in filaments tend to be preferentially aligned with the directions of the filaments, (4) the spin axes only have weak tendencies to be aligned with (or perpendicular to) the intermediate (or minor) axis of the local tidal tensor, etc. These measurements are very useful in our understanding of structure and galaxy formation, and can be used to constrain the spin and shape origin of galaxies. In addition, these alignment signals are also important in our modelling of the intrinsic weak lensing signals.
From halos to disks: the physics of angular momentum profiles
Bullock, James
The angular momentum distribution of dark matter as derived from dark matter only LCDM simulations provides an important starting point for interpreting galaxy disk sizes, however full hydrodynamics are required to get a complete picture. The gas that builds disk galaxies in the LCDM paradigm is typically accreted as cold along filaments, which are sourced with ~4 times more specific angular momentum than the dark matter. These filamentary cold flows deliver significant mass and angular momentum to galaxy halos, and provide an ample source for building large disk galaxies. A growing body of observational evidence suggests that this process is borne out in the real universe.
Accretion and growth of angular momentum in cosmological simulations
Genel, Shy
The role that cosmological simulations play in our pursuit to understand galaxy formation has revolutionized in the past few years with the modern generation of these simulations, and this holds in particular to studies of galaxy angular momentum acquisition and evolution. Large simulated galaxy populations that contain ballpark correct angular momentum facilitate a global description of how angular momentum flows in and out of galaxies, as well as being transported by mutual torques of various galaxy components. However, significant uncertainties persist both due to implementations of sub-grid and feedback models, as well as to the multitude, complexity, and non-linearity of the involved physical processes. In this talk I will review recent work based on cosmological hydrodynamical simulations, and discuss emerging trends regarding the dependence of galaxy angular momentum on dark matter halo properties, merger events, accretion of gas, and feedback.
Connecting angular momentum, mass and morphology: insights from the Magneticum simulations
Remus, Rhea-Silvia
Understanding the connection between the angular momentum properties of a galaxy and its formation history and thus its morphological properties is one of the most intriguing quests in extragalactic astrophysics. State-of-the-art hydrodynamical cosmological simulations of large volumes with sufficient resolution to trace galaxy properties over a large range of galaxy masses and redshifts are essential to disentangle the different processes in galaxy formation that lead to the huge variety in morphological and kinematical properties observed in present day galaxies, but only recently became available. One such simulation set are the Magneticum Pathfinder simulations. I will present insights obtained from these simulations with regard to the close connection between the angular momentum, the mass, and the morphology of galaxies, and how this is correlated to the individual formation pathways of galaxies. Furthermore, I will highlight the importance of observational measurements of the angular momentum of galaxies even though they are difficult to obtain. Finally, I will demonstrate how the kinematical properties measured with modern IFUs connect to the angular momentum evolution, and how this is correlated to galaxy properties at different redshifts.
Accretion physics and scaling laws of angular momentum in galaxies
Fraternali, Filippo
Star-forming galaxies must grow via continuous gas accretion from the surrounding environment. A key property of the accreting gas is its specific angular momentum, which plays a key role in determining the size of the final stellar disc. In this talk, I will present simple models of disc galaxy evolution, including chemical evolution, that help constraining the properties of the accreting gas. The comparison of these models with observations shows that: 1) disc galaxies grow in size today at a rate that is one third of their mass growth rate, 2) the accreting gas must rotate with a deficit of few tens of percent with respect to the disc rotation, 3) a nearly-isothermal hot corona can provide the accretion needed for the inside-out growth of galaxy discs. A relation that captures the properties of the accreting gas in connection with star formation and feedback is the stellar specific-angular-momentum vs mass relation. I will present a new determination of this relation extending to very low stellar masses and discuss its implications for disc evolution models.
The role of angular momentum in central and satellite early-type galaxies
Greene, Jenny
Integral-field units have opened the possibility to measure the degree of rotational support in large samples of early-type galaxies. While we have known for a long time that the degree of rotational support in a galaxy scales with stellar mass, it is now possible to ask whether central and satellite galaxies contain differences in their degree of rotation, relative to each other or as a function of halo mass. Thus far, studies with SAMI, MASSIVE, and MaNGA all agree that at fixed stellar mass, there is no measurable difference in the angular momentum content of galaxies as a function of large-scale environment, in agreement with current cosmological simulations. I discuss prospects to increase the fidelity of the measurements and examine redshift dependence in these relations.
Surprises in kinematic observations of early-type galaxies
Cappellari, Michele
I will summarize the status of our knowledge on the stellar kinematics of ETGs. I will place particular emphasis on new results and question raised from the large MaNGA integral-field spectroscopy surveys that we did not already know from Atlas3D.
Understanding the assembly histories of early-type galaxies from the kinematics of stars and globular clusters
Brodie, Jean
The SAGES Legacy Unifying Galaxies and GlobularS (SLUGGS) survey has generated large-scale, spatially resolved stellar kinematic data, along with high precision velocities for thousands of globular clusters (GCs), out to many effective radii in nearby early-type galaxies (ETGs). Although challenging to observe, the outskirts of galaxies retain valuable information about their assembly histories because of their longer dynamical time-scales and the fact that the majority of a galaxy’s angular momentum resides in its outskirts. We compare the kinematic properties of our galaxies with those from various simulated galaxies. Similarities and differences between predictions from simulations and these observational constraints are challenging our popular scenarios for ETG formation.
Angular momentum evolution of galaxies: the perspective of hydrodynamical simulations
Lagos, Claudia
Until a decade ago, galaxy formation simulations were unable to reproduce the high angular momentum that is typical of galaxy disks. Improvements in the interstellar medium and stellar feedback modelling, together with advances in computational capabilities, have allowed the current generation of cosmological galaxy formation simulations to reproduce the diversity of angular momentum and morphology that is observed in local galaxies. In this review I will discuss where we currently stand in this area from the perspective of hydrodynamical simulations, specifically how galaxies gain their angular momentum, and the effect galaxy mergers and gas accretion have on this process. I will show simulation results which suggest that a revision of the classical theory of disk formation is needed, and will finish by discussing what the challenges for simulations are.
Spatially resolved observations of angular momentum as a tracer of galaxy morphology and evolutionary history
Sweet, Sarah
Specific angular momentum (j) is a fundamental parameter in the evolution of galaxies, because it traces the tidal torques experienced during their lifetimes. The total j of a galaxy disk agrees with that of its dark matter halo, but the distributions are different, in that there is a lack of both low- and high-j baryons with respect to the CDM predictions. This discrepancy could arise during disk assembly if the baryons experience additional physical processes. For instance, gravitational torques due to interactions with neighbours in a dense environment can cause tidal stripping, removing outer, high-j material, while feedback due to AGN or stellar winds can remove inner, low-j material. Galaxy specific angular momentum is also related to its morphology. The distribution of j is different for disks and classical bulges; disks are expected to be dominated by rapidly-rotating material with a well-defined analytical solution x*exp(-kx), while bulges have little or no ordered rotation, Gaussian-smeared by random motions. The distribution of specific angular momentum PDF(j) therefore has two-fold utility: (1) comparison against model PDF(j) indicates the proportion of low-j and high-j material that has been lost, and the relative importance of feedback vs. tidal stripping; (2) the two-function fit can be used as a kinematic thin-disk decomposition. I will review the literature on this emerging topic and present my own work, illustrating how PDF(j) can inform us of a galaxy's morphology and evolutionary history with a spanning set of examples from present-day, cosmic-noon (z=1.5) and cosmic-noon analogue galaxies.
Stars re-shaping galaxies
Hopkins, Philip
The most fundamental unsolved problems in galaxy formation revolve around "feedback" from massive stars and black holes. I'll present new results from the FIRE simulations which combine new numerical methods and physics in an attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from stellar radiation pressure, supernovae, stellar winds, and photo-ionization. These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law and the global inefficiency of star formation -- the stellar mass function -- emerge naturally. Within galaxies, feedback regulates the structure of the interstellar medium, but more radically drives outflows which can actually change the dynamics, morphologies, and sizes of galaxies, in addition to transforming cusps into cores and suppressing star formation. This can radically re-distribute the angular momentum of galaxies, and leads to surprising conclusions about how galaxies settle into rotating systems (and whether or not this has anything to do with their sizes and other integrated properties).
Future high-redshift observations of HI kinematics
Blyth, Sarah
Recently, large optical IFU surveys have shown that angular momentum is tightly correlated with galaxy morphology and seems to be a key driver of galaxy formation and evolutionary processes. With SKA-pathfinder instruments coming online this year and the SKA1 hot on their heels, even deeper investigations of the role of angular momentum in galaxy evolution will be possible. In addition to the stellar angular momentum measurements from optical data, we will use radio observations to measure the contribution from the neutral hydrogen (HI) gas which, like most of the angular momentum, is located at larger effective radii than typically probed by IFU surveys. The exquisite sensitivity of these new radio telescopes will enable surveys which will probe HI kinematics (spatially resolved and unresolved) in thousands of galaxies to much higher redshifts than previously possible. I will discuss some of the possibilities for these studies using SKA and its pathfinders.
On the relationship between galaxy and halo size and spin
somerville, rachel
There is a long-standing ansatz that the angular momentum, and therefore the radial size, of galaxies is set by the spin of the host dark matter halo, and this ansatz forms the basis of galaxy size predictions in most semi-analytic models. I will present results from “structural abundance matching”, in which we empirically constrained the average relationship between galaxy size and halo virial radius from z~0 to z~3, using observations from the GAMA and CANDELS surveys. We found that this relationship exhibits a significant mass and redshift dependence, which suggests that halo spin is not the driving factor. I will discuss follow-up studies in which we explore the correlation between galaxy size and spin and halo properties in cosmological numerical hydrodynamical simulations from several groups (NIHAO, VELA, and Illustris) in order to gain insights into the physical origin of galaxy size and spin.
Angular momentum and the evolution of disc galaxies
Athanassoula, Lia
I use high resolution hydro-dynamical simulations of the formation and evolution of the disc component in spiral and lenticulars galaxies to establish and understand the link between angular momentum and radial stellar migration. I show that the latter determines the formation of the break in the stellar radial projected density profile as well as the inner and outer disc scale lengths. I will also discuss the redistribution of the angular momentum within the disc galaxy, and in particular the transfer of angular momentum from the inner parts of the disc (the bar/bulge region) to the halo, due to the bar growth and evolution. Thus I will show how the angular momentum redistribution is linked to the place of the galaxy in the SA / SB branches of disc galaxies in the Hubble diagram.
Does angular momentum regulate HI gas in isolated spirals?
Murugeshan, Chandrashekar
The neutral atomic hydrogen (HI) content of spiral galaxies has been observed to vary with environment, with more HI-poor or HI-deficient spirals being observed in high density environments. This has been attributed to influences such as ram pressure stripping and tidal interactions, which remove neutral hydrogen (HI) from the galaxies. However, some isolated spirals have also been observed to have relatively low HI mass fractions. The low densities of the Intra Galactic Medium in isolated environments make ram pressure stripping and tidal interactions unlikely candidates of gas removal. What then could be making some isolated spirals HI poor? Recently, Obreschkow et al. introduced the fHI - q relation (fHI is the HI mass fraction of a galaxy and q is the global stability parameter), where they find a tight positive correlation between the two parameters among isolated disk galaxies. The q parameter is directly linked to the specific angular momentum of the galaxy. The theoretical prediction is that this should be applicable to both HI excess and HI deficient disk galaxies. If this were to be true, then the HI deficiency in galaxies that reside in loose groups and fields can be explained not necessarily due to any stripping mechanisms but due to their low specific angular momentum. In order to verify this, we obtained high resolution HI data from the ATCA for 6 HI poor isolated spirals. In my talk, I will present the main results which indicate that our sample of HI deficient galaxies consistently follow the fHI - q relation. This result brings to light the importance of angular momentum in understanding the formation history of galaxies.
Untangling galaxy components: the angular momentum of bulges and disks in the MaNGA survey
Tabor, Martha
Deciphering where and when a galaxy's constituent stellar populations formed is crucial in understanding how that galaxy has formed and evolved. Photometric bulge-disk decompositions have long been used as a first order approximation of this; separating out the light from the central and extended components of a galaxy in order to compare colours and morphologies. However, photometric decompositions do not allow the determination of the kinematics of the individual stellar populations, which can reveal a great deal about the evolution history of a galaxy. We have therefore developed a method to extract the kinematics of multiple components in galaxies using IFU data and have applied it to a sample of MaNGA early type galaxies. This allows us to explore the angular momentum of bulges and disks separately and begin to understand the role each plays in determining the global angular momentum of a galaxy.
The extended Planetary Nebula Spectrograph (ePN.S) early-type galaxy (ETG) survey - Kinematic diversity and angular momentum at large radii
Pulsoni, Claudia
We present two-dimensional velocity and velocity dispersion fields, specific and total angular momentum profiles for 33 ETGs into their outer halos (average 6 effective radii, Re). We use Planetary nebulae (PNe) to trace the kinematics to these very large radii where absorption line spectroscopy is no longer feasible. The ePN.S survey is the largest survey to-date of ETG kinematics with PNe, based on data from the Planetary Nebula Spectrograph (PN.S), counter-dispersed imaging, and high-resolution PN spectroscopy. We find that ETGs typically show a kinematic transition between inner regions and halo. Slow rotators have increased but still modest rotational support at large radii. Most of our fast rotators show a decrease in rotation, due to the fading of the stellar disk in the outer, more slowly rotating spheroid. 30% of these fast rotators are dominated by rotation also at large radii, 40% show kinematic twists, misalignments, or rotation along two axes, indicating a transition from oblate to triaxial in the halo. Estimated transition radii in units of effective radii are ~ 1-3 Re and anti-correlate with stellar mass. These results are consistent with cosmological simulations and support a two-phase formation scenario for ETGs.
Spin evolution of Horizon-AGN early-type galaxies
Choi, Hoseung
The differential rotational properties of early-type galaxies (ETGs) revealed by integral field spectroscopy surveys is arguably one of the most exciting findings in the galaxy evolution study during the past decade. Numerical studies have shown that galaxy mergers under various configurations can reproduce the observed distribution of ETG spin. However, we suggest an alternative scenario for the spin evolution of a large fraction of ETGs. Using the Horizon-AGN simulation, we follow the spin evolution of 10,037 color-selected ETGs more massive than 1010 solar mass that are divided into four groups: cluster centrals (3%), cluster satellites (33%), group centrals(5%), and field ETGs (59%). We find a strong mass dependence of the slow rotator fraction, fSR, and the mean spin of massive ETGs. Although the environmental dependence is not clear in the fSR, it is visible in the mean value of the spin parameter. The environmental dependence is driven by the satellite ETGs whose spin gradually decreases as their environment becomes denser. Galaxy mergers appear to be the main cause of total spin changes in 94% of central ETGs of halos with Mvir > 1012.5 solar mass, but only 22% of satellite and field ETGs. We find that non-merger induced tidal perturbations better correlate with the galaxy spin-down in satellite ETGs than mergers. Given that the majority of ETGs are not central in dense environments, we conclude that non-merger tidal perturbation effects played a key role in the spin evolution of ETGs observed in the local (z < 1) universe.
The Assembly of Disk Galaxies: From Keck to JWST
Kassin, Susan
One of the most important open issues in astronomy is the assembly of galactic disks. Over the last decade this has been addressed with large surveys of internal galaxy kinematics spanning the last ~10 billion years of the universe. I will discuss recent results from my group that show the progressive (and mass-dependent) kinematic assembly of disk galaxies since a redshift of 2.5. We find that galactic angular momentum increases with time and is a strong function of the stellar mass of galaxies, even at high redshift. Our results strongly challenge traditional analytic models of galaxy formation and provide an important benchmark for simulations.Furthermore, I will discuss our plans for using the IFU and multi-object spectrograph on JWST/NIRSpec to enrich our understanding of galaxy kinematics to a redshift of 5, and to extend measurements to the much earlier universe. From mock JWST observations of simulations of galaxies, we are finding that interpreting these observations is not necessarily straightforward.
The angular momentum of galaxies and their haloes as a tracer of galaxy evolution
Posti, Lorenzo
Angular momentum (AM) is one of the pivotal variables determining the differentmorphologies of galaxies. While tidal torques should supply baryons and dark matterwith comparable amounts of AM, it is still unclear what determines which fraction ofthe available AM is eventually incorporated into the galaxies that we observe today.I will show how analytic models in a LCDM framework and the observed propertiesof galaxies (including recent measurements from the SPARC sample) can be foldedtogether to unveil how much AM is present in the gas available to cool and formstars in the galaxy. If star formation proceeds inside-out, from the innermostand AM-poorer regions, we find that (Posti et al. 2017 & 2018 subm.) i) spiralsneed to accrete a significant portion of AM-rich gas from the outer regions(10-50%), while ellipticals must have lost ~40% of the AM initially in the gasdue to mergers and dynamical friction; ii) the fraction of stellar-to-halo AM isa strong, non-linear function of galaxy mass for both morphological types.Comparing our estimate of the stellar-to-halo AM relation with the stellar-to-halomass relation, we find that the efficiencies of star formation and AM retentionclosely follow each other, indicating that the AM distribution of dark matterand baryons are also very well correlated. I will speculate on the constraintson galaxy formation that this implies.
S0 galaxies are faded spirals: clues from their angular momentum content
Rizzo, Francesca
The distribution of galaxies in the stellar specific angular momentum versus stellar mass plane (j*-M*) provides key insights into their formation mechanisms. In this talk I will show how I determined the location in this plane of a sample of ten field/group unbarred lenticular (S0) galaxies from the CALIFA survey. I performed a bulge-disc decomposition both photometrically and kinematically to study the stellar specific angular momentum of the disc components alone and understand the evolutionary links between S0s and other Hubble types. I found that eight of the S0 discs have a distribution in the j*-M* plane that is fully compatible with that of spiral discs, while only two have values of j* lower than the spirals. These two outliers show signs of recent merging. These results suggest that merger and interaction processes are not the dominant mechanisms in S0 formation in low-density environments. Instead, S0s appear to be the result of secular processes and the fading of spiral galaxies after the shutdown of star formation.
The Evolution of Baryonic Angular Momentum in Simulated Disk Galaxies
DeFelippis, Daniel
The angular momentum of a galaxy encapsulates its complicated evolution. A relationship between the angular momentum of the dark matter and stellar components of galaxies has been found, as well as a clear differentiation between low-angular momentum ellipticals and high-angular momentum disks. Simulations have shown that feedback ejects gas from disk galaxies and boosts its angular momentum while in the circumgalactic medium (CGM), but the details of how and extent to which the CGM affects the angular momentum of galaxies is not well understood. I will present an analysis of the baryonic angular momentum of galaxies in the Illustris simulation done by following gas as it accretes onto Milky-Way mass halos, becomes part of the galactic wind, and eventually forms stars. The winds change the angular momentum of the gas in several ways: from preventing angular momentum loss to increasing angular momentum through “fountains.” I will discuss these and other effects of similar magnitude, from which I conclude there is a complex origin of the similarity between the specific angular momenta of galactic disks and halos. I will also present subsequent analysis of the angular momentum distribution of the CGM for a large population of IllustrisTNG disk galaxies over many masses and redshifts. By distinguishing between dynamically distinct components of the gas based on its temperature, density, and radial motion, I will draw connections between the angular momentum of the CGM and the effect of baryonic feedback on the gas as it travels through the CGM. Although these results are not directly comparable to current observations, they will provide a strong foundation for future observational work studying the dynamics of the CGM.
NEW PERSPECTIVES ON GALACTIC ANGULAR MOMENTUM, GALAXY FORMATION, AND THE HUBBLE SEQUENCE
Fall, Michael
Galaxies of different Hubble type and bulge-to-total ratio (B/T) follow nearly parallel sequences in a plot of specific angular momentum (j = J/M) against mass M. This j-M diagram is a powerful tool for describing galaxies and for understanding in physical terms how they formed and evolved. Several years ago, Aaron Romanowsky and I made a major study of the galactic j-M diagram, based on extensive photometric and kinematic data for ~100 galaxies of all Hubble types spanning a wide range of masses (published in 2012 and 2013). This talk is based on an extension of our earlier work, highlighting results we have obtained in the past year (and not yet published). In particular, we now determine explicitly whether the angular momenta of bulges and disks are correlated with or independent of each other. This result places important constraints on formation mechanisms of galactic bulges, especially satellite capture versus disk instability. We also determine whether classical bulges and pseudo bulges follow similar or different relations in the j-M diagram (an issue raised by Obreschkow & Glazebrook 2014). This again has implications for how bulges formed. The results presented here also have a bearing on recent studies of the j-M diagram and the relation between the sizes of galaxies and the sizes of their dark halos at high redshifts. In particular, the z = 0 forms of these relations provide important anchors for their high-redshift counterparts.
Morphology and kinematics of the cold gas inside the central kiloparsec of nearby AGN with ALMA
Audibert, Anelise
One of the problem to fuel black holes and trigger the AGN is to remove a large amount of angular momentum to drive the gas to the center. The dynamical mechanisms invoked depend on the scale under consideration: at 10kpc scales, torques are produced by galaxy interactions and mergers; at kpc scales, bar instabilities, either internally driven by secular evolution, or triggered by a companion can first feed a central starburst and fuel the massive BH. At 100pc scales, the nested bars scenario, together with m=1 instabilities, are believed to dominate as dynamical mechanisms.Our goal is to probe the cold molecular gas in galaxy disks in a sample of nearby AGN (Seyfert/LINER), spanning more than a factor of 100 in AGN power (X-ray and radio luminosities), a factor of 10 in star formation rate (SFR), and a wide range of galaxy inner morphology. We aim at (i) identifying what are the mechanisms driving gas from the disk towards the nucleus, removing its large angular momentum and forming large non-axisymmetric perturbations and (ii) considering a large number of cases, deriving in which phase of their fuelling/feedback cycle they are observed, and deduce the different steps of the process.We will show the study of the morphology and kinematics of the cold dense gas inside the central kpc of 5 galaxies of our NUGA (NUclei of GAlaxies) program. We present ALMA observations of CO(3-2) and dense molecular gas tracers HCN(4-3), HCO+(4-3) and CS(7-6) for 5 galaxies with 0.14-0.3” resolution, centred on the nucleus and covering the whole nuclear disks and rings. We quantify the AGN fuelling by measuring torques on the gas computed from the stellar potential with the well-tested algorithm reported in Garc ´ia-Burillo et al. (2005); Combes et al. (2014).
Modelling the cosmic evolution and large-scale alignment of AM
Welker, Charlotte
Galaxies get angular momentum by cosmic gas infall from large-scale filaments. While merger-free disc galaxies should directly inherit from this gas infall, massive elliptical galaxies, for which most of the mass is assembled through mergers, obtain angular momentum differently than from smooth gas accretion. Those two different pictures of angular momentum acquisition lead to two significantly different signals of galaxy alignments in the cosmic web for discs and elliptical galaxies. I will show results from Horizon-AGN, a high-resolution hydrodynamical cosmological simulation, on galaxy alignments and the role played by feedback from active galactic nuclei in settling i) the change of morphology in massive galaxies, and ii) the reorientation of their angular momentum.
Spinning galaxies into shape
Foster, Caroline
Combining kinematic maps and imaging data for a generous sample of galaxies from the Sydney-AAO Multi Integral field (SAMI) Galaxy Survey, I empirically measure the relationship between the intrinsic (3D) shape of galaxies and spin. Most galaxies are oblate axisymmetric with varying degrees of intrinsic flattening. Low spin systems have a higher occurrence of triaxiality and high spin systems are more intrinsically flattened and axisymmetric. I argue that angular momentum plays a fundamental and primary role in shaping galaxies. Based on outer balance in dynamical support, I further suggest that at fixed spin, the visual morphology (e.g. presence of spiral arms) is likely set by other processes such as gas content and merger history.