Aaron A. Dutton, Stéphane Courteau
The scaling relations between rotation velocity, size and luminosity form a benchmark test for any theory of disk galaxy formation. We confront recent theoretical models of disk formation to a recent large compilation of such scaling relations. We stress the importance of achieving a fair comparison between models and observations.
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The first convincing piece of evidence of spiral structure in the accretion disc in IP Pegasi was found by Steeghs et al. (1997). We performed two kinds of 2D hydrodynamic simulations, a SFS finite volume scheme and a SPH scheme, with a mass ratio of 0.5. Both results agreed well with each other. We constructed Doppler maps and line flux-binary phase relations based on density distributions, the results agreeing well with those obtained by observation.
We compare the properties of local spiral galaxies with the predictions of the Cole et al. semi-analytic model of hierarchical galaxy formation, in order to gain insight into the baryonic processes that were responsible for shaping these galaxies. On the whole, the models reproduce the properties of present-day spirals (such as SFRs, SFHs, scale sizes, metallicities, and gas fractions) rather well. In particular, we find that once the effects of dust and variations in stellar populations have been taken into account, published spiral galaxy scale-size distributions derived from optical data (w…
We investigate the star formation activity in galaxy pairs in chemical hydrodynamical simulations consistent with a Lambda-CDM scenario. A statistical analysis of the effects of galaxy interactions on the star formation activity as a function of orbital parameters shows that close encounters (r < 30 kpc/h) can be effectively correlated with an enhancement of star formation activity with respect to galaxies without a close companion. Our results suggest that the stability properties of systems are also relevant in this process. We found that the passive star forming galaxies pairs tend to have …
We analyze the structural and dynamical properties of disk-like objects formed in fully consistent cosmological simulations which include inefficient star formation. Comparison with data of similar observable properties of spiral galaxies gives satisfactory agreement, in contrast with previous findings using other codes. This suggests that the stellar formation implementation used has allowed the formation of disks as well as guaranteed their stability.
Utilizing spatially resolved VLT/FORS spectroscopy and HST/ACS imaging, we constructed a sample of over 200 field spiral galaxies at redshifts 0.1<z<1.0. We find that the ratio between stellar and total mass remains roughly constant over the observed epochs, in compliance with the framework of hierarchical structure growth. However, the stellar mass-to-light ratios evolve more strongly in low-mass spirals than in high--mass spirals, indicating an anti-hierarchical evolution of their stellar populations (aka "down-sizing").
The distributions of size and luminosity for star-forming regions in the nearby spiral galaxy NGC 628 are studied over a wide range of scales using progressively blurred versions of an image from the Hubble Space Telescope Advanced Camera for Surveys. Four optical filters are considered for the central region, including Halpha. Two filters are used for an outer region. The features in each blurred image are counted and measured using SExtractor. The cumulative size distribution is found to be a power law in all passbands with a slope of about -1.5 over 1.8 orders of magnitudes. The luminosity …
We present an extragalactic perspective of an extended stellar tidal stream wrapping around the edge-on, spiral galaxy NGC 5907. Our deep images reveal for the first time a large scale complex of arcing loops that is an excellent example of how a low-mass satellite accretion can produce an interwoven, rosette-like structure of debris dispersed in the halo of its host galaxy. The existence of this structure, which has probably formed and survived for several Gigayears, confirms that halos of spiral galaxies in the Local Universe may still contain a significant number of galactic fossils from th…
We have discovered three globular clusters beyond the Holmberg radius in Hubble Space Telescope Advanced Camera for Surveys images of the gas-rich dark matter dominated blue compact dwarf galaxy NGC2915. The clusters, all of which start to resolve into stars, have M_{V606} = -8.9 to -9.8 mag, significantly brighter than the peak of the luminosity function of Milky Way globular clusters. Their colors suggest a metallicity [Fe/H] ~ -1.9 dex, typical of metal-poor Galactic globular clusters. The specific frequency of clusters is at a minimum normal, compared to spiral galaxies. However, since onl…
A release of multicolor broad band (BVRI) photometry for a subsample of 44 isolated spirals drawn from the Catalogue of Isolated Galaxies (CIG) is presented. Total magnitudes and colors at various circular apertures, as well as some global structural/morphological parameters are estimated. Morphology is reevaluated through optical and sharp/filtered R band images, (B-I) color index maps, and archive near-IR JHK images from the Two-Micron Survey. The CAS structural parameters (Concentration, Asymmetry, and Clumpiness) were calculated from the images in each one of the bands. The fraction of gal…
Combining a theoretical model of mass accretion onto a galactic center with a high-resolution $N$-body/SPH simulation, we investigate the formation of an intermediate massive black hole (IMBH) during the hierarchical formation of a small spiral galaxy (with a total mass of $10^{10}M_{\odot}$) in the high-$z$ universe. We found that the rate of average mass accretion to the nucleus due to the radiation drag exerted by newly formed stars in the forming galaxy is $\approx 10^{-5}M_{\odot}$yr$^{-1}$. As a result of this accretion, an IMBH with $\approx 10^{4}M_{\odot}$ can be formed in the center …
We use the bulge Sersic index n and bulge-to-total ratio (B/T) to explore the fundamental question of how bulges form. We perform 2D bulge-disk-bar decomposition on H-band images of 143 bright, high stellar mass (>1.0e10 solar masses) low-to-moderately inclined (i<70 degrees) spirals. Our results are: (1) Our H-band bar fraction (~58%) is consistent with that from ellipse fits. (2) 70% of the stellar mass is in disks, 10% in bars, and 20% in bulges. (3) A large fraction (~69%) of bright spirals have B/T<0.2, and ~76% have low n<2 bulges. These bulges exist in barred and unbarred galaxies acros…
In the last few years, galaxies at redshifts up to z~1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10m-class telescopes. With kinematic and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation (TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially resolved rotation curves of 78 spiral galaxies in the…
We analyze the structural and dynamical properties of disk-like objects formed in fully consistent cosmological simulations with an inefficient star formation algorithm. Comparison with data of similar observable properties of spiral galaxies gives satisfactory agreement.
Recent observations have revealed a class of unusually HI-rich early-type galaxies. By combining observations of their morphology, stellar populations and neutral hydrogen we aim to understand how these galaxies fit into the hierarchical formation paradigm. Here we present the result of our radio and optical observations of a test case galaxy, the E/S0 IC 4200.
The study of satellite galaxies can provide information on the merging and aggregation processes which, according to the hierarchical clustering models, form the larger spiral galaxies we observe. With the aim of testing hierarchical models of galaxy formation, we have conducted an observational program which comprises H$α$ imaging for both the parent and the satellite galaxies, taken from the compilation by Zaritsky et al. (1997) that contains 115 galaxies orbiting 69 primary isolated spiral galaxies. We have observed a subsample of 37 spiral and irregular galaxies taken from the compilation …
We study the chemical and spectro-photometric evolution of galactic disks with detailed models calibrated on the Milky Way and using simple scaling relations, based on currently popular semi-analytic models of galaxy formation. We compare our results to a large body of observational data on present day galactic disks, including: disk sizes and central surface brightness, Tully-Fisher relations in various wavelength bands, colour-colour and colour-magnitude relations, gas fractions vs. magnitudes and colours, abundances vs. local and integrated properties, as well as spectra for different galac…
Spiral galaxies offer a unique opportunity to study the role of star formation in galaxy evolution and to test various theoretical star formation schemes. I review some recent relevant work on the evolution of spiral galaxies. Detailed models are used for the chemical and spectrophotometric evolution, with metallicity dependent stellar yields, tracks and spectra. The models are ``calibrated'' on the Milky Way disk and generalised to other spirals with some simple scaling relations, obtained in the framework of Cold Dark Matter models for galaxy formation. The results compare favourably to the …
High-resolution N-body re-simulations of 15 massive (10^{14}-10^{15} Msun) dark matter haloes have been combined with the hybrid galaxy formation model GalICS (Hatton et al. 2003), to study the formation and evolution of galaxies in clusters, within the framework of the hierarchical merging scenario. New features in GalICS include a better description of galaxy positioning within dark matter haloes, a more reliable computation of the temperature of the inter-galactic medium as a function of redshift, and a description of the ram pressure stripping process. We focus on the luminosity functions,…
Young stellar groupings and clusters have hierarchical patterns ranging from flocculent spiral arms and star complexes on the largest scale to OB associations, OB subgroups, small loose groups, clusters and cluster subclumps on the smallest scales. There is no obvious transition in morphology at the cluster boundary, suggesting that clusters are only the inner parts of the hierarchy where stars have had enough time to mix. The power-law cluster mass function follows from this hierarchical structure: n(M_cl) M_cl^-b for b~2. This value of b is independently required by the observation that the …
We suggest that the bulge-to-disc ratios of spiral galaxies are primarily determined by the angular momenta of their host haloes predicted in current hierarchical clustering models for structure formation. Gas with low specific angular momentum becomes self-gravitating and presumably forms stars before it can settle into a rotationally supported disc. We assume this part of the gas in a dark halo to form a bulge, while the rest is assumed to settle into a rotationally supported disc. With these assumptions the predicted bulge-to-disc ratios in mass and in size, and other correlations between t…
Hierarchical galaxy formation models make specific predictions concerning the relative assembly rates and star formation histories of spiral bulges and field ellipticals. Independently of the cosmological model and initial power spectrum of fluctuations, at all epochs the stellar populations in spiral bulges should be older and redder than those in typical ellipticals selected at the same redshift. To test this simple prediction, we analyze the internal optical colors of a complete sample of I<24 mag early-type and spiral galaxies from the Northern and Southern Hubble Deep Fields (HDF). The su…
We investigate the hierarchical build-up of stars in bulges within the standard $Λ$-cold dark matter scenario. By separating the population into stars born during starbursts that accompany the formation of spheroids in major mergers ({\it starburst} component), and stars that are previously formed in discs of progenitor galaxies ({\it quiescent} component) and added to the spheroid by dynamical interaction. Our results are summarised as follows: bulges that form early have larger starburst fraction and hence should be smaller than their counter parts that form later. The quiescent fraction in …
Based on VLT/FORS spectroscopy and HST/ACS imaging, we have constructed a sample of ~200 field spiral galaxies that cover redshifts up to z~1. Such a large data set allows to study the evolution of fundamental galaxy parameters like luminosity, size, mass, mass-to-light ratio etc. as a function of cosmic time and in various mass regimes. Several of our findings - like the time-independent fraction of stellar-to-total mass - are in compliance with a hierarchical structure growth. However, the stellar population properties of intermediate-redshift disks favour a down-sizing scenario in the sense…
Star-formation within galaxies appears on multiple scales, from spiral structure, to OB associations, to individual star clusters, and often sub-structure within these clusters. This multitude of scales calls for objective methods to find and classify star-forming regions, regardless of spatial size. To this end, we present an analysis of star-forming groups in the local group spiral galaxy M33, based on a new implementation of the Minimum Spanning Tree (MST) method. Unlike previous studies which limited themselves to a single spatial scale, we study star-forming structures from the effective …
High resolution gravity plus smoothed particle hydrodynamics simulations are used to study the formation of galaxies within the context of hierarchical structure formation. The simulations have sufficient dynamic range to resolve from ten kpc scale galactic disks up to many Mpc scale filaments. Over this range of scales, we find that hierarchical structure development proceeds through a series of increasingly larger filamentary collapses. The well resolved simulated galaxies contain hundreds to thousands of particles and have varied morphologies covering the entire expected range from disks to…
We have gained VLT/FORS spectra and HST/ACS images of a sample of 220 distant field spiral galaxies. Spatially resolved rotation curves were extracted and fitted with synthetic velocity fields that take into account all geometric and observational effects, like blurring due to the slit width and seeing influence. The maximum rotation velocity Vmax could be determined for 124 galaxies that cover the redshift range 0.1<z<1.0. The luminosity-rotation velocity distribution of this sample is offset from the Tully-Fisher relation (TFR) of local low-mass spirals, whereas the distant high-mass spirals…
We present our project on galaxy evolution in the environment of distant rich clusters aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of field galaxies. Spatially resolved MOS spectra were gained with VLT/FORS to analyze the internal kinematics of disk galaxies. First results are shown for the clusters MS 1008.1-1224 (z=0.30), Cl 0303+1706 (z=0.42), and Cl 0413-6559 (z=0.51). Out of 35 late type cluster members, 13 galaxies exhibit a rotation curve of the universal form rising in the inner region and passing ov…
We have performed a large observing campaign of intermediate-redshift disk galaxies including spectroscopy with the FORS instruments of the VLT and imaging with the Advanced Camera for Surveys onboard the HST. Our data set comprises 113 late-type galaxies in the redshift range 0.1<z<1.0 and thereby probes galaxy evolution over more than half the age of the universe. Spatially resolved rotation curves have been extracted and fitted with synthetic velocity fields that account for geometric distortions and blurring effects. With these models, the intrinsic maximum rotation velocity Vmax was deriv…
Using high-resolution N-body/SPH simulations with $2\times 10^6$ particles, we investigate the evolution of stellar and gaseous galactic cores during the hierarchical formation of a spiral galaxy. We find that the galactic core ($r < 300 $ pc) coevolves with the host galaxy. The average mass ratio between the baryonic core and the halo is nearly constant, $\sim $ 0.04 from $z \sim 10$ to $z \sim 2$. However, there are several `rapid-growing phases' during the evolution, in which the rate of mass accretion to the central sub-kpc region is ten times higher ($\sim 1 M_\odot$ yr pc$^{-1}$) than th…
Observational determinations of the correlation between the characteristic density delta_c and the virial mass M_vir of dark halos constitute a critical test for models of hierarchical structure formation. Using the dynamical properties of dark halos reconstructed from the galaxy distributions in massive systems (groups/clusters) and the rotation curves in less massive systems (dwarf, low surface brightness and spiral galaxies) drawn from the literature, we confirm the existence of the delta_c-M_vir relation over a broad mass range from 10**10 to 10**15 solar masses, which is in gross consiste…
We present results from a careful and detailed analysis of the structural and dynamical properties of a sample of 29 disc-like objects identified at z=0 in three AP3M-SPH fully consistent cosmological simulations. These simulations are realizations of a CDM hierarchical model, where an inefficient Schmidt law-like algorithm to model the stellar formation process has been implemented. We focus on properties that can be constrained with available data from observations of spiral galaxies, namely, the bulge and disc structural parameters and the rotation curves. Comparisons with data from Broeils…
We follow the evolution of disk galaxies within a cluster that forms hierarchically in a cold dark matter N-body simulation. At a redshift z=0.5 we select several dark matter halos that have quiet merger histories and are about to enter the newly forming cluster environment. The halos are replaced with equilibrium high resolution model spirals that are constructed to represent examples of low surface brightness (LSB) and high surface brightness (HSB) galaxies. Varying the disk and halo structural parameters reveals that the response of a spiral galaxy to tidal encounters depends primarily on t…
Within the hierarchical framework for galaxy formation, merging and tidal interactions are expected to shape large galaxies to this day. While major mergers are quite rare at present, minor mergers and satellite disruptions - which result in stellar streams - should be common, and are indeed seen in both the Milky Way and the Andromeda Galaxy. As a pilot study, we have carried out ultra-deep, wide-field imaging of some spiral galaxies in the Local Volume, which has revealed external views of such stellar tidal streams at unprecedented detail, with data taken at small robotic telescopes (0.1-0.…
We study the photometric parameters of the bulges of galaxies of different Hubble types including ellipticals, lenticulars, early and late type spirals and early type dwarf galaxies. Analyzing the distributions of various photometric parameters, and two- and three-dimensional correlations between them, we find that there is a difference in the correlations exhibited by bright (M_K < -22) and faint bulges, irrespective of their Hubble type. Importantly, the bright bulges, which include typically E/S0 galaxies and bulges of early type spirals, are tightly distributed around a common photometric …
We describe the GALFORM semi-analytic model for calculating the formation and evolution of galaxies in hierarchical models. It improves upon, and extends, the Cole et al 1994 model. The model employs a new Monte-Carlo algorithm to follow the merging evolution of dark matter halos with arbitrary mass resolution. It incorporates realistic descriptions of the density profiles of dark matter halos and their gas content; follows the chemical evolution of gas and stars, and the associated production of dust; and includes a detailed calculation of the sizes of disks and spheroids. Wherever possible, …
We review the topic of rotation curves of spiral galaxies emphasizing the standard interpretation as evidence for the existence of dark matter halos. Galaxies other than spirals and late-type dwarfs may also possess great amounts of dark matter, and therefore ellipticals, dwarf spirals, lenticulars and polar ring galaxies are also considered. Furthermore, other methods for determining galactic dark matter, such as those provided by binaries, satellites or globular clusters, have to be included. Cold dark matter hierarchical models constitute the standard way to explain rotation curves, and thu…
Multiple, sequential mergers are unavoidable in the hierarchical build-up picture of galaxies, in particular for the minor mergers that are frequent and highly likely to have occured several times for most present-day galaxies. However, the effect of repeated minor mergers on galactic structure and evolution has not been studied systematically so far. We present a numerical study of multiple, subsequent, minor galaxy mergers, with various mass ratios ranging from 4:1 to 50:1. The N-body simulations include gas dynamics and star formation. We study the morphological and kinematical properties o…
Our unified chemical and spectrophotometric evolution code allows to simultaneously study the ISM abundances of a series of elements and the spectral properties of the stellar population in our model galaxies. We use stellar evolutionary tracks, yields, spectra, color and absorption index calibrations for 5 different metallicities and account for the increase in initial metallicity of successive generations of stars. For any kind of stellar system, as described by its star formation history and IMF, we thus can directly compare the time evolution of gaseous and stellar abundance ratios. Spiral…
The possibility that the Galactic spheroid was assembled from numerous chemically-distinct, proto-Galactic fragments is investigated using a Monte-Carlo technique designed to simulate the chemical evolution of the Galaxy in hierarchical formation scenarios which involve no gas dissipation. By comparing the observed and simulated metallicity distributions of Galactic globular clusters and halo field stars, we estimate the level of fragmentation in the collapsing proto-Galaxy. Although the formation process is highly stochastic, the simulations often show good agreement with the observed metalli…
Six subclusters in the Coma cluster have been selected on the basis of a hierarchical clustering method that takes the gravitational interaction among galaxies into account. Of these, three main subclusters around the galaxies NGC 4889, NGC 4874, and NGC 4839 have been singled out. We have used the objective statistical criterion applied by Vennik and Anosova in studies of close groups of galaxies to evaluate each member included in a subcluster with a high probability. Galaxies with a significant deficit of hydrogen HI, including objects from the Bravo-Alfaro list,have been identified with me…
Galaxies exhibit a sequence of various morphological types, i.e., the Hubble sequence, and they are basically composed of spheroidal components (elliptical galaxies and bulges in spiral galaxies) and disks. It is known that spheroidal components are found only in relatively massive galaxies with M=10^{10-12} M_sun, and all stellar populations in them are very old, but there is no clear explanation for these facts. Here we present a speculative scenario for the origin of the Hubble sequence, in which magnetic fields ubiquitously seen in galaxies have played a crucial role. We first start from a…
The unprecedented resolution of the refurbished Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST) has led to major advances in our understanding of galaxy formation. The high image quality in the Medium Deep Survey and Hubble Deep Field has made it possible, for the first time, to classify faint distant galaxies according to morphological type. These observations have revealed a large population of galaxies classed as irregulars or which show signs of recent merger activity. Their abundance rises steeply with apparent magnitude, providing a likely explanation for th…
In the current galaxy formation scenarios, two physical phenomena are invoked to build disk galaxies: hierarchical mergers and more quiescent external gas accretion, coming from intergalactic filaments. Although both are thought to play a role, their relative importance is not known precisely. Here we consider the constraints on these scenarios brought by the observation-deduced star formation history on the one hand, and observed dynamics of galaxies on the other hand: the high frequency of bars and spirals, the high frequency of perturbations such as lopsidedness, warps, or polar rings. All …
I discuss the formation of alpha-enhanced metal-rich stellar populations in the nuclei of luminous ellipticals. Based on hierarchical clustering, different galaxy formation scenarios, which imply different star formation histories, are considered. In contrast to the fast clumpy collapse mode, the late merger of two spiral galaxies fails to reproduce significantly $α$-enhanced abundance ratios, unless the IMF is flattened. Following the star formation history predicted by semi-analytic models of hierarchical clustering for the average elliptical, solar abundance ratios are obtained with Salpete…
A review of gravitational and hydrodynamical processes during formation of clusters and evolution of galaxies is given. Early, at the advent of N-body computer simulations, the importance of tidal fields in galaxy encounters has been recognized. Orbits are crowded due to tides along spiral arms, where the star formation is enhanced. Low relative velocity encounters lead to galaxy mergers. The central dominating galaxies in future clusters form before the clusters in a merging process in galaxy groups. Galaxy clusters are composed in a hierarchical scenario due to relaxation processes between g…
We study the effects of mergers on the structural properties of disc-like systems by using Smooth Particle Hydrodynamical (SPH) numerical simulations in hierarchical clustering scenarios. In order to assess the effects of mergers on the mass distributions we performed a bulge-disc decomposition of the projected surface density of the systems at different stages of the merger process. We assumed an exponential law for the disc component and the Sérsic law for the bulges. We found that simulated objects at $z=0$ have bulge profiles with shape parameters $n\approx 1$, consistent with observationa…
(Abridged) This paper presents an exploration of two fundamental scaling relations of spiral galaxies, the luminosity-rotation speed (or Tully-Fisher; TF) relation, and the size-luminosity (SL) relation, and the dependences of their scatter, at red and IR bands. We verify that the observed virial relations of disk galaxies are given by Vobs \prop L^0.31 and Rd \prop L^0.33 using distance-redshift surveys of high surface brightness (HSB) and low surface brightness (LSB) non-interacting galaxies. Thus the galaxy surface brightness (SB) is Sigma \prop Rd \prop Vobs \prop Mvir^0.33. We derive the …
We introduce our project on galaxy evolution in the environment of rich clusters aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of galaxies in the field. Emphasis is laid on the examination of the internal kinematics of disk galaxies through spatially resolved MOS spectroscopy with FORS at the VLT. First results are presented for the clusters MS1008.1-1224 (z=0.30), Cl0303+1706 (z=0.42), and Cl0413-6559 (F1557.19TC) (z=0.51). Out of 30 cluster members with emission-lines, 13 galaxies exhibit a rotation curve of…
(abridged) Studies of distant galaxies have shown that ellipticals and large spirals were already in place 8 Gyr ago, leading to a very modest recent star formation in intermediate mass galaxies. This is challenged by a recent analysis (Heavens et al. 2004) of the fossil record of the stellar populations of ~10^5 nearby galaxies, which show that intermediate mass galaxies have formed or assembled the bulk of their stars 4 to 8 Gyr ago. Here we present direct observational evidence supporting the Heavens et al's findings from a long term, multi-wavelength study of 195 z>0.4 intermediate mass ga…
We have conducted an observing campaign with FORS at the ESO-VLT to explore the kinematical properties of spiral galaxies in distant galaxy clusters. Our main goal is to analyse transformation- and interaction processes of disk galaxies within the special environment of clusters as compared to the hierarchical evolution of galaxies in the field. Spatially resolved MOS-spectra have been obtained for seven galaxy clusters at 0.3<z<0.6 to measure rotation velocities of cluster members. For three of the clusters, Cl0303+17, Cl0413-65, and MS1008-12, for which we presented results including a TF-di…
Understanding galaxy formation involves look-back and fossil-record studies of distant and nearby galaxies, respectively. Debris trails in our Galaxy's spheroidal halo of old stars provide evidence of "bottom-up" formation via tidal disruption/merging of dwarf satellite galaxies, but it is difficult to study our Galaxy's large-scale structure from within. Studies of our neighbouring Andromeda galaxy have concluded that its spheroid contains chemically enriched ("metal-rich") stars out to a radius of 30 kiloparsecs with an exponential r^1/4 fall-off in density thereby resembling a galactic "bul…
The globular cluster (GC) systems of the Milky Way and of our neighboring spiral galaxy, M31, comprise 2 distinct entities, differing in 3 respects. 1. M31 has young GCs, ages from ~100 Myr to 5 Gyr old, as well as old globular clusters. No such young GCs are known in the Milky Way. 2. We confirm that the oldest M31 GCs have much higher nitrogen abundances than do Galactic GCs at equivalent metallicities. 3. Morrison et al. found M31 has a subcomponent of GCs that follow closely the disk rotation curve of M31. Such a GC system in our own Galaxy has yet to be found. These data are interpreted i…
In current $Λ$CDM galaxy formation scenarios, at least three physical phenomena could contribute to the mass assembly: monolithic collapse, hierarchical mergers and more quiescent external gas accretion, with secular evolution. The three processes are described, and their successes and problems are reviewed. It is shown that monolithic collapse is likely to be quite restricted to sub-components of galaxies, while the two main scenarii, hierarchical merging and secular evolution, might have comparable roles, depending on environment. Evidences are reviewed for the important role of gas accretio…
We present results of numerical simulations of the formation of a massive counterrotating gas disk in a spiral galaxy. Using a hierarchical tree gravity solver combined with a sticky-particle gas dissipation scheme for our simulations, we have investigated three mechanisms: episodic and continuous gas infall, and a merger with a gas-rich dwarf galaxy. We find that both episodic and continuous gas infall work reasonably well and are able to produce a substantial gas counterrotating disk without upsetting the stability of the existing disk drastically, but it is very important for the gas to be …
We analyse the skewness of the line-of-sight velocity distributions in model elliptical galaxies built through collisionless galaxy mergers. We build the models using large N-body simulations of mergers between either two spiral or two elliptical galaxies. Our aim is to investigate whether the observed ranges of skewness coefficient (h3) and the rotational support (V/sigma), as well as the anticorrelation between h3 and V, may be reproduced through collisionless mergers. Previous attempts using N-body simulations failed to reach V/sigma ~ 1-2 and corresponding high h3 values, which suggested t…
We calculate the spatial two-point auto and cross-correlation functions for the 765 galaxies with Rc<21.5 and 0.1<z<0.51 in the ESO-Sculptor survey, and explore the segregation effects among the populations of giant (early-type, late spiral) and dwarf (dE, dI) galaxies. At separation of 0.3 h^-1 Mpc, pairs of early-type galaxies dominate the clustering over all the other types of pairs. At intermediate scales, 0.3-5 h^-1 Mpc, mixed pairs of dwarf and giant galaxies contribute equally as pairs of giant galaxies, whereas the latter dominate at ~10 h^-1 Mpc. We detect the signature of the transit…
This is a summary of a general discussion held during the third EuroConference on galaxy evolution. Various observational features of the stellar populations in present--day dwarf galaxies were presented to introduce the discussion on the possibility that these systems be the main building blocks of spiral and elliptical galaxies. Many people in the audience turned out to think that the inconsistencies among the observed properties of large and dwarf galaxies are too many to believe that the former are built up only by means of successive accretions of the latter. However, theorists of hierarc…
We have performed intermediate-resolution VLT/FORS spectroscopy and HST/ACS imaging of 129 field spiral galaxies within the FORS Deep Field. The galaxies cover the redshift range 0.1 < z < 1.0 and comprise all types from Sa to Sdm/Im. Spatially resolved rotation curves were extracted and fitted with synthetic velocity fields that take into account all geometric (e.g., inclination and misalignment) and observational effects (in particular, blurring due to optical beam smearing and seeing). Using these fits, the maximum rotation velocity Vmax could be determined for 73 objects. The Tully-Fisher …
Galaxy evolution is in transition from an early universe dominated by hierarchical clustering to a future dominated by secular processes. These result from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos. This paper summarizes a review by Kormendy & Kennicutt (2004) using, in part, illustrations of different galaxies. In simulations, bars rearrange disk gas into outer rings, inner rings, and galactic centers, where high gas densities feed starbursts. Consistent with this picture, many barred and oval galaxies have dense central co…
We present a morphological study of the galaxy population of the luminous X-ray cluster MS1054-03 at z=0.83. The sample consists of 81 spectroscopically confirmed cluster members in a 3 x 2 Mpc area imaged in F606W and F814W with WFPC2. We find thirteen ongoing mergers in MS1054-03, comprising 17% of the L > L* cluster population. Most of these mergers will likely evolve into luminous (\sim 2 L*) elliptical galaxies, and some may evolve into S0 galaxies. Assuming the galaxy population in MS1054-03 is typical for its redshift it is estimated that \sim 50% of present-day cluster ellipticals expe…
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