The structural and photometric properties of early-type galaxies in hierarchical models (original) (raw)
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Galaxy luminosities, stellar masses, sizes, velocity dispersions as a function of morphological type
Monthly Notices of the Royal Astronomical Society, 2010
We provide fits to the distribution of galaxy luminosity, size, velocity dispersion and stellar mass as a function of concentration index C r and morphological type in the SDSS. (Our size estimate, a simple analog of the SDSS cmodel magnitude, is new: it is computed using a combination of seeing-corrected quantities in the SDSS database, and is in substantially better agreement with results from more detailed bulge/disk decompositions.) We also quantify how estimates of the fraction of 'early' or 'late' type galaxies depend on whether the samples were cut in color, concentration or light profile shape, and compare with similar estimates based on morphology. Our fits show that ellipticals account for about 20% of the r-band luminosity density, ρ Lr , and 25% of the stellar mass density, ρ * ; including S0s and Sas increases these numbers to 33% and 40%, and 50% and 60%, respectively. The values of ρ Lr and ρ * , and the mean sizes, of E, E+S0 and E+S0+Sa samples are within 10% of those in the Hyde & Bernardi (2009), C r ≥ 2.86 and C r ≥ 2.6 samples, respectively. Summed over all galaxy types, we find ρ * ∼ 3 × 10 8 M ⊙ Mpc −3 at z ∼ 0. This is in good agreement with expectations based on integrating the star formation history. However, compared to most previous work, we find an excess of objects at large masses, up to a factor of ∼ 10 at M * ∼ 5 × 10 11 M ⊙ . The stellar mass density further increases at large masses if we assume different IMFs for elliptical and spiral galaxies, as suggested by some recent chemical evolution models, and results in a better agreement with the dynamical mass function.
Cosmic star formation: constraints on the galaxy formation models
Monthly Notices of the Royal Astronomical Society, 2004
We study the evolution of the cosmic star formation in the universe by computing the luminosity density (in the UV, B, J, and K bands) and the stellar mass density of galaxies in two reference models of galaxy evolution: the pure-luminosity evolution (PLE) model developed by and the semi-analytical model (SAM) of hierarchical galaxy formation by . The former includes a detailed description of the chemical evolution of galaxies of different morphological types; it does not include any number evolution of galaxies whose number density is normalized to the observed local value. On the other hand, the SAM includes a strong density evolution following the formation and the merging histories of the DM haloes hosting the galaxies, as predicted by the hierarchical clustering scenario, but it does not contain morphological classification nor chemical evolution. Our results suggest that at low-intermediate redshifts (z < 1.5) both models are consistent with the available data on the luminosity density of galaxies in all the considered bands. At high redshift the luminosity densities predicted in the PLE model show a peak due to the formation of ellipticals, whereas in the hierarchical picture a gradual decrease of the star formation and of the luminosity densities is predicted for z > 2.5. At such redshifts the PLE predictions tend to overestimate the present data in the B band whereas the SAM tends to underestimate the observed UV luminosity density. As for the stellar mass density, the PLE picture predicts that nearly 50% and 85% of the present stellar mass are in place at z ∼ 4 and z ∼ 1, respectively. According to the hierarchical SAM, 50% and 60% of the present stellar mass are completed at z ∼ 1.2 and z = 1, respectively. Both predictions fit the observed stellar mass density evolution up to z = 1. At z > 1, the PLE and SAM models tend to overestimate and underestimate the observed values, respectively. We discuss the origin of the similarities and of the discrepancies between the two models, and the role of observational uncertainties (such as dust extinction) in comparing models with observations.
A comparison of stellar populations in galaxy spheroids across a wide range of Hubble types
Monthly Notices of the Royal Astronomical Society, 2002
We present line-strengths and kinematics from the central regions of 32 galaxies with Hubble types ranging from E to Sbc. Spectral indices, based on the Lick system, are measured in the optical and near infra-red (NIR). The 24 indices measured, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy and allow estimation of enhancements in specific light elements (particularly C and Mg). The large range of Hubble types observed allows direct comparison of line-strengths in the centres of early-type galaxies (E and S0) with those in spiral bulges, free from systematic differences that have plagued comparisons of results from different studies. Our sample includes field and Virgo cluster galaxies. For early-type galaxies our data are consistent with previously reported trends of Mg 2 and Mgb with velocity dispersion. In spiral bulges we find trends in all indices with velocity dispersion. We estimate luminosity-weighted ages, metallicities and heavy element abundance ratios (enhancements) from optical indices. These show that bulges are less enhanced in light (α-capture) elements and have lower average age than earlytype galaxies. Trends involving age and metallicity also differ sharply between early and late types. An anti-correlation exists between age and metallicity in early types, while, in bulges, metallicity is correlated with velocity dispersion. We consider the implications of these findings for models of the formation of these galaxies. We find that primordial collapse models of galaxy formation are ruled out by our observations, while several predictions of hierarchical clustering (merger) models are confirmed.
Monthly Notices of the Royal Astronomical Society, 2018
We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into 'passive' and 'star-forming' classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < z < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift.
Evolution of the Hubble sequence in hierarchical models for galaxy formation
Monthly Notices of the Royal Astronomical Society, 1996
We present a model for the broad morphological distinction between the disk and spheroidal components of galaxies. Elaborating on the hierarchical clustering scheme of galaxy formation proposed by Cole et al, we assume that galaxies form stars quiescently in a disk until they are disrupted into a spheroidal configuration by mergers. Bulges and spheroids may continue to accrete gas from their hot coronae, and so they may grow disks again. Thus, an individual galaxy may pass through various phases of disk or spheroid dominance during its lifetime. To distinguish between disks and spheroids we add one additional free parameter to the semianalytic model of Cole et al. which we fix by requiring that the predicted morphological mix should match that observed locally. Assuming an Ω = 1, standard cold dark matter cosmology, we calculate formation and merging histories, and the evolution in colour, luminosity and morphology of the galaxy populations in different environments. Our model predicts that the bulges of spirals were assembled before the spheroids of ellipticals and the spheroids of cluster ellipticals were assembled before those of field ellipticals. About 50% of ellipticals, but only about 15% of spirals, have undergone a major merger during the redshift interval 0.0 ≤ z ≤ 0.5. In spite of their violent formation history, elliptical galaxies turn out to have colourmagnitude diagrams with remarkably small scatter. Apart from a general blueing of the galaxy population with redshift, the colour-magnitude diagrams are remarkably similar at redshift z = 0.5 and at the present day. The morphological mix of galaxies that become rich cluster members at high redshift is dominated by spiral galaxies, due to the long timescale for galaxy mergers compared with the timescale for cluster assembly at high redshift. The assembly of low redshift clusters is slower, allowing more galaxy mergers to occur in the progenitor halos. As a result z = 0 rich clusters become E/S0 dominated and we find a "Butcher-Oemler" effect that becomes weaker for poorer groups at high redshift. The field luminosity function of red galaxies shows little evolution out to z ≃ 1 and the reddest galaxies at these redshifts are as bright as their local counterparts. The blue luminosity function, on the other hand, evolves rapidly with redshift, increasing its characteristic luminosity and becoming steeper at the faint end. These trends are similar to those recently observed in the Canada-France Redshift Survey. Our calculations serve to demonstrate that a simple prescription for the distinction between disks and spheroids that is compatible with hierarchical clustering goes a long way towards explaining many of the systematic trends observed in the galaxy population.
The Growth of Galaxies in Cosmological Simulations of Structure Formation
The Astrophysical Journal, 2002
We use hydrodynamic simulations to examine how the baryonic components of galaxies are assembled, focusing on the relative importance of mergers and smooth accretion in the formation of ∼ L * systems. In our primary simulation, which models a (50h −1 Mpc) 3 comoving volume of a Λ-dominated cold dark matter universe, the space density of objects at our (64-particle) baryon mass resolution threshold M c = 5.4 × 10 10 M ⊙ corresponds to that of observed galaxies with L ∼ L * /4. Galaxies above this threshold gain most of their mass by accretion rather than by mergers. At the redshift of peak mass growth, z ≈ 2, accretion dominates over merging by about 4:1. The mean accretion rate per galaxy declines from ∼ 40M ⊙ yr −1 at z = 2 to ∼ 10M ⊙ yr −1 at z = 0, while the merging rate peaks later (z ≈ 1) and declines more slowly, so by z = 0 the ratio is about 2:1. We cannot distinguish truly smooth accretion from merging with objects below our mass resolution threshold, but extrapolating our measured mass spectrum of merging objects, dP/dM ∝ M −α with α ∼ 1, implies that sub-resolution mergers would add relatively little mass. The global star formation history in these simulations tracks the mass accretion rate rather than the merger rate. At low redshift, destruction of galaxies by mergers is approximately balanced by the growth of new systems, so the comoving space density of resolved galaxies stays nearly constant despite significant mass evolution at the galaxy-by-galaxy level. The predicted merger rate at z 1 agrees with recent estimates from close pairs in the CFRS and CNOC2 redshift surveys.
Disk galaxy formation and evolution: models up to intermediate redshifts
Arxiv preprint astro-ph/9810293, 1998
Making use of a seminumerical method we develop a scenario of disk galaxy formation and evolution in the framework of inflationary cold dark matter (CDM) cosmologies. Within the virializing dark matter halos, disks in centrifugal equilibrium are built-up and their galactic evolution is followed through an approach which considers the gravitational interactions among the galaxy components, the turbulence and energy balance of the ISM, the star formation (SF) process due to disk gravitational instabilities, the stellar evolution and the secular formation of a bulge. We find that the main properties and correlations of disk galaxies are determined by the mass, the hierarchical mass aggregation history and the primordial angular momentum. The models follow the same trends across the Hubble sequence than the observed galaxies. The predicted TF relation is in good agreement with the observations except for the standart CDM. While the slope of this relation remains almost constant up to intermediate redshifts, its zero-point decreases in the H-band and slightly increases in the B-band. A maximum in the SF rate for most of the models is attained at z ∼ 1.5 − 2.5.
Dark Halo and Disk Galaxy Scaling Laws in Hierarchical Universes
The Astrophysical Journal, 2000
We use cosmological N-body/gasdynamical simulations that include star formation and feedback to examine the proposal that scaling laws between the total luminosity, rotation speed, and angular momentum of disk galaxies reflect analogous correlations between the structural parameters of their surrounding dark matter halos. The numerical experiments follow the formation of galaxy-sized halos in two Cold Dark Matter dominated universes: the standard Ω = 1 CDM scenario and the currently popular ΛCDM model. We find that the slope and scatter of the I-band Tully-Fisher relation are well reproduced in the simulations, although not, as proposed in recent work, as a result of the cosmological equivalence between halo mass and circular velocity: large systematic variations in the fraction of baryons that collapse to form galaxies and in the ratio between halo and disk circular velocities are observed in our numerical experiments. The Tully-Fisher slope and scatter are recovered in this model as a direct result of the dynamical response of the halo to the assembly of the luminous component of the galaxy. We conclude that models that neglect the self-gravity of the disk and its influence on the detailed structure of the halo cannot be used to derive meaningful estimates of the scatter or slope of the Tully-Fisher relation. Our models fail, however, to match the zero-point of the Tully-Fisher relation, as well as that of the relation linking disk rotation speed and angular momentum. These failures can be traced, respectively, to the excessive central concentration of dark halos formed in the Cold Dark Matter cosmogonies we explore and to the formation of galaxy disks as the final outcome of a sequence of merger events. Disappointingly, our feedback formulation, calibrated to reproduce the empirical correlations linking star formation rate and gas surface density established by Kennicutt, has little influence on these conclusions. Agreement between model and observations appears to demand substantial revision to the Cold Dark Matter scenario or to the manner in which baryons are thought to assemble and evolve into galaxies in hierarchical universes.
Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies
The Astrophysical Journal, 2016
Published mass models fitted to galaxy rotation curves are used to study the systematic properties of dark matter (DM) halos in late-type and dwarf spheroidal (dSph) galaxies. Halo parameters are derived by fitting non-singular isothermals to (V 2 −V 2 vis) 1/2 , where V (r) is the observed rotation curve and V vis is the rotation curve of the visible matter. The latter is calculated from the surface brightness assuming that the mass-to-light ratio M/L is constant with radius. "Maximum disk" values of M/L are adjusted to fit as much of the inner rotation curve as possible without making the halo have a hollow core. Rotation curve decomposition becomes impossible fainter than absolute magnitude M B ≃ −14, where V becomes comparable to the velocity dispersion of the gas. To increase the luminosity range further, we include dSph galaxies, which are physically related to spiral and irregular galaxies. Combining the data, we find that DM halos satisfy well defined scaling laws analogous to the "fundamental plane" relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii r c , higher central densities ρ 0 , and smaller central velocity dispersions σ. Scaling laws provide new and detailed constraints on the nature of DM and on galaxy formation and evolution. Some simple implications include: 1-A single, continuous physical sequence of increasing mass extends from dSph galaxies with M B ≃ −7.6 to Sc I galaxies with M B ≃ −22.4. 2-The high DM densities in dSph galaxies are normal for such tiny galaxies. Since virialized density depends on collapse redshift z coll , ρ 0 ∝ (1 + z coll) 3 , the smallest dwarfs formed at least ∆z coll ≃ 7 earlier than the biggest spirals. 3-The high DM densities of dSphs implies that they are real galaxies formed from primordial density fluctuations. They are not tidal fragments. Tidal dwarfs cannot retain even the low DM densities of their giant-galaxy progenitors. In contrast, dSphs have higher DM densities than do giant-galaxy progenitors. 4-The fact that, as luminosity decreases, dwarf galaxies become much more numerous and also more nearly dominated by DM raises the possibility that there exists a large population of objects that are completely dark. Such objects are a canonical prediction of cold DM theory. If they exist, "empty halos" are likely to be small and dense-that is, darker versions of Draco and UMi. 5-The slopes of the DM parameter correlations provide a measure on galactic mass scales of the slope n of the power spectrum |δ k | 2 ∝ k n of primordial density fluctuations. Our preliminary results not yet corrected for baryonic compression of DM give n ≃ −1.9 ± 0.2. This is consistent with cold DM theory.
The Astrophysical Journal, 2007
We derive the luminosity functions of elliptical galaxies, galaxy bulges, galaxy pseudo-bulges and galaxy discs from our structural catalogue of 10,095 galaxies. In addition we compute their associated luminosity and stellar mass densities. We show that spheroidal systems (elliptical galaxies and the bulges of disc galaxies) exhibit a strong color bimodality indicating two distinct types of spheroid which are separated by a core color of (u − r) ∼ 2 mag. We argue that the similarity of the red elliptical and the red bulge luminosity functions supports our previous arguments that they share a common origin and surprisingly find that the same follows for the blue ellipticals and blue bulges, the latter of which we refer to as pseudo-bulges. In terms of the stellar mass budget we find that 58 ± 6 per cent is currently in the form of discs, 39 ± 6 per cent in the form of red spheroids (13 ± 4 per cent ellipticals, 26±4 per cent bulges) and the remainder is in the form of blue spheroidal systems (∼ 1.5 per cent blue ellipticals and ∼ 1.5 per cent pseudo-bulges). In terms of galaxy formation we argue that our data on galaxy components strongly supports the notion of a two-stage formation process (spheroid first, disc later) but with the additional complexity of secular evolution occurring in quiescent discs giving rise to two distinct bulge types: genuine 'classical' bulges and pseudo-bulges. We therefore advocate that there are three significant structures underpinning galaxy evolution: classical spheroids (old); pseudobulges (young) and discs (intermediate). The luminous nearby galaxy population is a mixture of these three structural types. The nature of the blue elliptical galaxies remains unclear but one possibility is that these constitute recently collapsed structures supporting the notion of mass-dependent spheroid formation with redshift.