Monthly Notices of the Royal Astronomical Society, 2001
We study the biasing relation between dark matter haloes or galaxies and the underlying mass dist... more We study the biasing relation between dark matter haloes or galaxies and the underlying mass distribution, using cosmological N-body simulations in which galaxies are modelled via semi-analytic recipes. The non-linear, stochastic biasing is quantified in terms of the mean biasing function and the scatter about it as a function of time, scale and object properties. The biasing of galaxies and haloes shows a general similarity and a characteristic shape, with no galaxies in deep voids and a steep slope in moderately underdense regions. At a comoving scale of ,8 h 21 Mpc, the non-linearity in the biasing relation is typically &10 per cent and the stochasticity is a few tens of per cent, corresponding to ,30 per cent variations in the cosmological parameter b V 0X6 abX Biasing depends weakly on halo mass, galaxy luminosity, and scale. The observed trend with luminosity is reproduced when dust extinction is included. The time evolution is rapid, with the mean biasing larger by a factor of a few at z , 3 compared with z 0Y and with a minimum for the non-linearity and stochasticity at an intermediate redshift. Biasing today is a weak function of the cosmological model, reflecting the weak dependence on the power-spectrum shape, but the time evolution is more cosmology-dependent, reflecting the effect of the growth rate. We provide predictions for the relative biasing of galaxies of different type and colour, to be compared with upcoming large redshift surveys. Analytic models in which the number of objects is conserved underestimate the evolution of biasing, while models that explicitly account for merging provide a good description of the biasing of haloes and its evolution, suggesting that merging is a crucial element in the evolution of biasing.
We present Keck I MOSFIRE spectroscopy in the Y and H bands of GDN-8231, a massive, compact, star... more We present Keck I MOSFIRE spectroscopy in the Y and H bands of GDN-8231, a massive, compact, star-forming galaxy at a redshift of z∼1.7. Its spectrum reveals both Hαand [N II]emission lines and strong Balmer absorption lines. The Hαand Spitzer MIPS24 μm fluxes are both weak, thus indicating a low star-formation rate of SFR 5 10- M yr −1. This, added to a relatively young age of ∼700 Myr measured from the absorption lines, provides the first direct evidence for a distant galaxy being caught in the act of rapidly shutting down its star formation. Such quenching allows GDN-8231 to become a compact, quiescent galaxy, similar to threeother galaxies in our sample, by z∼1.5. Moreover, the color profile of GDN-8231 shows a bluer center, consistent with the predictions of recent simulations for an early phase of inside-out quenching. Its line-of-sight velocity dispersion for the gas, gas LOS s =127±32 km s −1 , is nearly 40% smaller than that of its stars, LOS s =215±35 km s −1. Highresolution hydro-simulations of galaxies explain such apparently colder gas kinematics of up to a factor of ∼1.5 with rotating disks being viewed at different inclinations and/or centrally concentrated star-forming regions. A clear prediction is that their compact, quiescent descendants preserve some remnant rotation from their starforming progenitors.
We introduce a new color-selection technique to identify high-redshift, massive galaxies that are... more We introduce a new color-selection technique to identify high-redshift, massive galaxies that are systematically missed by Lyman-break selection. The new selection is based on the H 160 (H) and Infrared Array Camera (IRAC) 4.5 µm bands, specifically H − [4.5] > 2.25 mag. These galaxies, dubbed "HIEROs", include two major populations that can be separated with an additional J − H color. The populations are massive and dusty star-forming galaxies at z > 3 (JH-blue) and extremely dusty galaxies at z 3 (JH-red). The 350 arcmin 2 of the GOODS-North and GOODS-South fields with the deepest HST/WFC3 near-infrared and IRAC data contain as many as 285 HIEROs down to [4.5] < 24 mag. Inclusion of the most extreme HIEROs, not even detected in the H band, makes this selection particularly complete for the identification of massive high-redshift galaxies. We focus here primarily on JH-blue (z > 3) HIEROs, which have a median photometric redshift z ∼ 4.4 and stellar mass M * ∼ 10 10.6 M ⊙ and are much fainter in the rest-frame UV than similarly massive Lyman-break galaxies (LBGs). Their star formation rates (SFRs), derived from their stacked infrared spectral energy distributions, reach ∼240 M ⊙ yr −1 leading to a specific SFR, sSFR ≡ SFR/M * ∼ 4.2 Gyr −1 , suggesting that the sSFRs for massive galaxies continue to grow at z > 2 but at a lower growth rate than from z = 0 to z = 2. With a median half-light radius of 2 kpc, including ∼20% as compact as quiescent galaxies at similar redshifts, JH-blue HIEROs represent perfect star-forming progenitors of the most massive (M * 10 11.2 M ⊙) compact quiescent galaxies at z ∼ 3 and have the right number density. HIEROs make up ∼60% of all galaxies with M * > 10 10.5 M ⊙ identified at z > 3 from their photometric redshifts. This is five times more than LBGs with nearly no overlap between the two populations. While HIEROs make up 15-25% of the total SFR density at z ∼ 4-5, they completely dominate the SFR density taking place in M * > 10 10.5 M ⊙ galaxies, and HIEROs are therefore crucial to understanding the very early phase of massive galaxy formation.
Galaxies with stellar masses near M * contain the majority of stellar mass in the universe, and a... more Galaxies with stellar masses near M * contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present-day stellar masses near M * , at 5 × 10 10 M (defined here to be MW-mass) and 10 11 M (defined to be M31-mass). We study the typical progenitors of these galaxies using the FourStar Galaxy Evolution Survey (ZFOURGE). ZFOURGE is a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z ∼ 3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star formation rates, combining our deep multiwavelength imaging with near-IR Hubble Space Telescope imaging from Cosmic Near-IR Deep Extragalactic Legacy Survey (CANDELS), and Spitzer and Herschel far-IR imaging from Great Observatories Origins Deep Survey-Herschel and CANDELS-Herschel. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages to redder dust-obscured IR-luminous galaxies in intermediate stages and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of two to three lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star formation in present-day M * galaxies, requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and SFRs imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z ∼ 0 and are strongly anticorrelated with an increase in the Sérsic index. Therefore, the growth of galaxy bulges in M * galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star formation efficiency.
Monthly Notices of the Royal Astronomical Society, 1995
The mass density field in the local universe, recovered by the potent method from peculiar veloci... more The mass density field in the local universe, recovered by the potent method from peculiar velocities of ∼3000 galaxies, is compared with the density field of optically selected galaxies. Both density fields are smoothed with a Gaussian filter of radius 12h −1 Mpc. Under the assumptions of gravitational instability and a linear biasing parameter b O between optical galaxies and mass, we obtain β O ≡ Ω 0.6 /b O = 0.74±0.13. This result is obtained from a regression of potent mass density on optical density after correcting the mass density field for systematic biases in the velocity data and potent method. The error quoted is just the 1σ formal error estimated from the observed scatter in the density-density scatterplot; it does not include the uncertainty due to cosmic scatter in the mean density or in the biasing relation. We do not attempt a formal analysis of the goodness of fit, but the scatter about the fit is consistent with our estimates of the uncertainties.
Elements of kinematical and dynamical modeling of elliptical galaxies are presented. In projectio... more Elements of kinematical and dynamical modeling of elliptical galaxies are presented. In projection, NFW models resemble Sérsic models, but with a very narrow range of shapes (m = 3 ± 1). The total density profile of ellipticals cannot be NFW-like because the predicted local M/L and aperture velocity dispersion within an effective radius (Re) are much lower than observed. Stars must then dominate ellipticals out to a few Re. Fitting an NFW model to the total density profile of Sérsic+NFW (stars+dark matter [DM]) ellipticals results in very high concentration parameters, as found by X-ray observers. Kinematical modeling of ellipticals assuming an isotropic NFW DM model underestimates M/L at the virial radius by a factor of 1.6 to 2.4, because dissipationless ΛCDM halos have slightly different density profiles and slightly radial velocity anisotropy. In N-body+gas simulations of ellipticals as merger remnants of spirals embedded in DM halos, the slope of the DM density profile is steeper when the initial spiral galaxies are gas-rich. The Hansen & Moore (2006) relation between anisotropy and the slope of the density profile breaks down for gas and DM, but the stars follow an analogous relation with slightly less radial anisotropies for a given density slope. Using kurtosis (h4) to infer anisotropy in ellipticals is dangerous, as h4 is also sensitive to small levels of rotation. The stationary Jeans equation provides accurate masses out to 8 Re. The discrepancy between the modeling of Romanowsky et al. (2003), indicating a dearth of DM in ellipticals, and the simulations analyzed by Dekel et al. (2005), which match the spectroscopic observations of ellipticals, is partly due to radial anisotropy and to observing oblate ellipticals face-on. However, one of the 15 solutions to the orbit modeling of Romanowsky et al. is found to have an amount and concentration of DM consistent with ΛCDM predictions.
We determine the intrinsic, three-dimensional shape distribution of star-forming galaxies at 0 < ... more We determine the intrinsic, three-dimensional shape distribution of star-forming galaxies at 0 < z < 2.5, as inferred from their observed projected axis ratios. In the present-day universe, star-forming galaxies of all masses 10 9-10 11 M are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M * > 10 10 M) disks are the most common geometric shape at all z 2. Lower-mass galaxies at z > 1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 10 9 M (10 10 M) are a mix of roughly equal numbers of elongated and disk galaxies at z ∼ 1 (z ∼ 2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z ∼ 1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks.
We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-... more We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-resolution cosmological N-body simulation of a ΛCDM cosmology. At each analyzed redshift z we divide the dark matter particles into 4 components: (i) isolated galactic halos, (ii) subhalos, (iii) the diffuse medium of group and cluster halos, and (iv) the background outside of virialized halos. We follow the time evolution of the mass distribution and flows between these components and provide fitting functions for the exchange rates. The exchange rates show gradual evolution as z decreases to 2, and become more steady thereafter. For z < ∼ 2 about 15% of the isolated galactic halos cluster per Gyr to become subhalos and a similar fraction of their mass returns to the unvirialized background. Mass accumulation onto subhalos is equally shared between previously isolated halos and unvirialized matter, and is dominated by accretion from the host's diffuse matter beyond z ≃ 1. This accumulation is balanced for z ≃ 0.5 by subhalo disruption at a rate of about half of their mass per Gyr. The diffuse component in host halos is built by accreting isolated halos and un-virialized material in mass shares of 40% and 60%, respectively, and at z < 0.5 also by disruption of subhalos. The unvirialized IGM is enriched mostly by stripping of isolated halos, and at z < 1 also by mass loss from groups and clusters. We go on to use our derived exchange rates together with a simple recipe for metal production to gauge the importance of metal redistribution in the universe due solely to gravity-induced interactions. This crude model predicts some trends regarding metallicity ratios. The diffuse metallicity in clusters is predicted to be ∼ 40% that in isolated galaxies (∼ 55% of groups) at z = 0, and should be lower only slightly by z = 1, consistent with observations. The metallicity of the diffuse media in large galaxy halos and poor groups is expected to be lower by about a factor of 5 by z ∼ 2, in agreement with the observed metallicity of damped Lyα systems. The metallicity of the background IGM is predicted to be (1 − 3) × 10 −4 that of z = 0 clusters, also consistent with observations. The agreement of predicted and observed trends indicates that gravitational interaction alone may play an important role in metal enrichment of the intra-cluster and intergalactic media.
One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legac... more One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to z ≈ 8. Its two-tiered "wide and deep" strategy bridges significant gaps in existing near-infrared surveys. Here we report on z ≈ 8 galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers 50.1 arcmin 2 to 4 ks depth in each of three near-infrared bands in the Great Observatories Origins Deep Survey southern field. Two of our candidates have J < 26.2 mag, and are > 1 mag brighter than any previously known F105W-dropouts. We derive constraints on the bright-end of the rest-frame ultraviolet luminosity function of galaxies at z ≈ 8, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in Spitzer Infrared Array Camera images, which are the first such individual detections at z ≈ 8. Their derived stellar masses are on the order of a few ×10 9 M ⊙ , from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at z ≈ 8. The high number density of very luminous and very massive galaxies at z ≈ 8, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.
We discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster us... more We discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. As a result the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z ≃ 1.6 to the present, growing as (1 + z) −0.6±0.1. If this result is generalizable, then it implies that physical processes associated with the denser cluster region seems to have caused accelerated size growth in quiescent galaxies prior to z = 1.6 and slower subsequent growth at z < 1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z < 1 clusters.
We allow for nonlinear effects in the likelihood analysis of galaxy peculiar velocities, and obta... more We allow for nonlinear effects in the likelihood analysis of galaxy peculiar velocities, and obtain ∼ 35%-lower values for the cosmological density parameter Ω m and for the amplitude of mass-density fluctuations σ 8 Ω 0.6 m. This result is obtained under the assumption that the power spectrum in the linear regime is of the flat ΛCDM model (h = 0.65, n = 1, COBE normalized) with only Ω m as a free parameter. Since the likelihood is driven by the nonlinear regime, we "break" the power spectrum at k b ∼ 0.2 (h −1 Mpc) −1 and fit a power-law at k > k b. This allows for independent matching of the nonlinear behavior and an unbiased fit in the linear regime. The analysis assumes Gaussian fluctuations and errors, and a linear relation between velocity and density. Tests using mock catalogs that properly simulate nonlinear effects demonstrate that this procedure results in a reduced bias and a better fit. We find for the Mark III and SFI data Ω m = 0.32 ± 0.06 and 0.37 ± 0.09 respectively, with σ 8 Ω 0.6 m = 0.49 ± 0.06 and 0.63 ± 0.08, in agreement with constraints from other data. The quoted 90% errors include distance errors and cosmic variance, for fixed values of the other parameters. The improvement in the likelihood due to the nonlinear correction is very significant for Mark III and moderately significant for SFI. When allowing deviations from ΛCDM, we find an indication for a wiggle in the power spectrum: an excess near k ∼ 0.05 (h −1 Mpc) −1 and a deficiency at k ∼ 0.1 (h −1 Mpc) −1-a "cold flow". This may be related to the wiggle seen in the power spectrum from redshift surveys and the second peak in the CMB anisotropy. A χ 2 test applied to modes of a Principal Component Analysis (PCA) shows that the nonlinear procedure improves the goodness of fit and reduces a spatial gradient that was of concern in the purely linear analysis. The PCA allows us to address spatial features of the data and to evaluate and fine-tune the theoretical and error models. It demonstrates in particular that the models used are appropriate for the cosmological parameter estimation performed. We address the potential for optimal data compression using PCA.
* , lines in Fig. 1]. For galaxies with robust 24 mm detections (mJy), SFRs were derived followin... more * , lines in Fig. 1]. For galaxies with robust 24 mm detections (mJy), SFRs were derived following Le Floc'h et al. f 1 60 L44
Using high resolution N-body simulations with hydrodynamics and star formation, we investigate in... more Using high resolution N-body simulations with hydrodynamics and star formation, we investigate interactions and the resulting starbursts in galaxies with properties typical of $z\sim 3$. We apply spectral population models to produce mock-HST images, and discuss the observed magnitude, color, and morphological appearance of our simulated galaxies in both the rest-UV and rest-visual bands.
We study the distribution functions of mass and circular velocity for dark matter halos in N-body... more We study the distribution functions of mass and circular velocity for dark matter halos in N-body simulations of the $\Lambda$CDM cosmology, addressing redshift and environmental dependence. The dynamical range enables us to resolve subhalos and distinguish them from "distinct" halos. The mass function is compared to analytic models, and is used to derive the more observationally relevant circular velocity function. The distribution functions in the velocity range 100--500 km/s are well fit by a power-law with two parameters, slope and amplitude. We present the parameter dependence on redshift and provide useful fitting formulae. The amplitudes of the mass functions decrease with z, but, contrary to naive expectation, the comoving density of halos of a fixed velocity ~200 km/s actually increases out to z=5. This is because high-z halos are denser, so a fixed velocity corresponds to a smaller mass. The slope of the velocity function at z=0 is as steep as ~ -4, and the mass ...
Monthly Notices of the Royal Astronomical Society, 2013
We have exploited the Hubble Space Telescope (HST) Cosmic Assembly Near-IR Deep Extragalactic Leg... more We have exploited the Hubble Space Telescope (HST) Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) J and H-band Wide Field Camera 3 (WFC3)/infrared (IR) imaging to study the properties of (sub-)millimetre galaxies within the Great Observatories Origins Deep Survey South (GOODS-South) field. After using the deep radio (Very Large Array 1.4 GHz) and Spitzer (Infrared Array Camera 8 µm) imaging to identify galaxy counterparts for the (sub-)millimetre sources, we have then utilized the new CANDELS WFC3/IR imaging in two ways. First, the addition of new deep near-IR photometry from both HST and (at K band) the VLT to the existing GOODS-South data base has enabled us to derive improved photometric redshifts and stellar masses, confirming that the (sub-)millimetre sources are massive (M = 2.2 × 10 11 ± 0.2 M) galaxies at z 1−3. Secondly, we have exploited the depth and resolution of the WFC3/IR imaging to determine the sizes and morphologies of the galaxies at rest-frame optical wavelengths λ rest > 4000 Å. Specifically, we have fitted two-dimensional axisymmetric galaxy models to the WFC3/IR images, varying luminosity, axial ratio, half-light radius r 1/2 and Sérsic index n. Crucially, the wavelength and depth of the WFC3/IR imaging enables modelling of the mass-dominant galaxy, rather than the blue high surface-brightness features which often dominate optical (rest-frame ultraviolet) images of (sub-)millimetre galaxies, and can confuse visual morphological classification. As a result of this analysis, we find that >95 per cent of the rest-frame optical light in almost all of the (sub-)millimetre galaxies is well described by either a single exponential disc (n 1), or a multiple-component system in which the dominant constituent is disc like. We demonstrate that this conclusion is completely consistent with the results of recent high-quality groundbased K-band imaging sampling even longer rest-frame wavelengths, and explain why it is so. These massive disc galaxies are reasonably extended (r 1/2 = 4.5 ± 0.5 kpc; median r 1/2 = 4.0 kpc), consistent with the sizes of other massive star-forming discs at z 2. In many cases, we find evidence of blue clumps within the sources, with the mass-dominant disc component becoming more significant at longer wavelengths. Finally, only a minority of the sources show
Monthly Notices of the Royal Astronomical Society, 2010
We use high-resolution cosmological hydrodynamical adaptive mesh refinement (AMR) simulations to ... more We use high-resolution cosmological hydrodynamical adaptive mesh refinement (AMR) simulations to predict the characteristics of Lyα emission from the cold gas streams that fed galaxies in massive haloes at high redshift. The Lyα luminosity in our simulations is powered by the release of gravitational energy as gas flows from the intergalactic medium into the halo potential wells. The ultraviolet UV background contributes only <20 per cent to the gas heating. The Lyα emissivity is due primarily to electron-impact excitation cooling radiation in gas at ∼2 × 10 4 K. We calculate the Lyα emissivities assuming collisional ionization equilibrium at all gas temperatures. The simulated streams are self-shielded against the UV background, so photoionization and recombination contribute negligibly to the Lyα line formation. We produce theoretical maps of the Lyα surface brightnesses, assuming that ∼85 per cent of the Lyα photons are directly observable. We do not consider transfer of the Lyα radiation, nor do we include the possible effects of internal sources of photoionization such as star-forming regions. Dust absorption is expected to obscure a small fraction of the luminosity in the streams. We find that typical haloes of mass M v ∼ 10 12-10 13 M at z ∼ 3 emit as Lyα blobs (LABs) with luminosities 10 43-10 44 erg s −1. Most of the Lyα comes from the extended (50-100 kpc) narrow, partly clumpy, inflowing, cold streams of (1-5) × 10 4 K that feed the growing galaxies. The predicted LAB morphology is therefore irregular, with dense clumps and elongated extensions. The integrated area contained within surface brightness isophotes of 2 × 10 −18 erg s −1 cm −2 arcsec −2 is ∼2-100 arcsec 2 , consistent with observations. The linewidth is expected to range from 10 2 to more than 10 3 km s −1 with a large variance. The typical Lyα surface brightness profile is ∝ r −1.2 where r is the distance from the halo centre. Our simulated LABs are similar in luminosity, morphology and extent to the observed LABs, with distinct kinematic features. The predicted Lyα luminosity function is consistent with observations, and the predicted areas and linewidths roughly recover the observed scaling relations. This mechanism for producing LABs appears inevitable in many high-z galaxies, though it may work in parallel with other mechanisms. Some of the LABs may thus be regarded as direct detections of the cold streams that drove galaxy evolution at high z.
Monthly Notices of the Royal Astronomical Society, 2011
We investigate the origin of the relations between stellar mass and optical circular velocity for... more We investigate the origin of the relations between stellar mass and optical circular velocity for early-type (ETG) and late-type (LTG) galaxies-the Faber-Jackson (FJ) and Tully-Fisher (TF) relations. We combine measurements of dark halo masses (from satellite kinematics and weak lensing), and the distribution of baryons in galaxies (from a new compilation of galaxy scaling relations), with constraints on dark halo structure from cosmological simulations. The principle unknowns are the halo response to galaxy formation and the stellar initial mass function (IMF). The slopes of the TF and FJ relations are naturally reproduced for a wide range of halo response and IMFs. However, models with a universal IMF and universal halo response cannot simultaneously reproduce the zero points of both the TF and FJ relations. For a model with a universal Chabrier IMF, LTGs require halo expansion, while ETGs require halo contraction. A Salpeter IMF is permitted for high mass (σ ∼ > 180 km s −1) ETGs, but is inconsistent for intermediate masses, unless V circ (R e)/σ e ∼ > 1.6. If the IMF is universal and close to Chabrier, we speculate that the presence of a major merger may be responsible for the contraction in ETGs while clumpy accreting streams and/or feedback leads to expansion in LTGs. Alternatively, a recently proposed variation in the IMF disfavors halo contraction in both types of galaxies. Finally we show that our models naturally reproduce flat and featureless circular velocity profiles within the optical regions of galaxies without fine-tuning.
Monthly Notices of the Royal Astronomical Society, 2011
There are strong correlations between the three structural properties of elliptical galaxiesstell... more There are strong correlations between the three structural properties of elliptical galaxiesstellar mass, velocity dispersion and size-in the form of a tight 'Fundamental Plane' and a 'scaling relation' between each pair. Major mergers of disc galaxies are assumed to be a mechanism for producing ellipticals, but semi-analytic galaxy formation models (SAMs) have encountered apparent difficulties in reproducing the observed slope and scatter of the size-mass relation. We study the scaling relations of merger remnants using progenitor properties from two SAMs. We apply a simple merger model that includes gas dissipation and star formation based on theoretical considerations and simulations. Combining the SAMs and the merger model allows the calculation of the structural properties of the remnants of major mergers that enter the population of elliptical galaxies at a given redshift. Without tuning the merger model parameters for each SAM, the results roughly match the slope and scatter in the observed scaling relations and their evolution in the redshift range z = 0-3. Within this model, the observed scaling relations, including the tilt of the Fundamental Plane relative to the virial plane, result primarily from the decrease of gas fraction with increasing progenitor mass. The scatter in the size-mass relation of the remnants is reduced from that of the progenitors because of a correlation between progenitor size and gas fraction at a given mass.
Monthly Notices of the Royal Astronomical Society, 2008
We construct a physically motivated model for predicting the properties of the remnants of gaseou... more We construct a physically motivated model for predicting the properties of the remnants of gaseous galaxy mergers, given the properties of the progenitors and the orbit. The model is calibrated using a large suite of SPH merger simulations. It implements generalized energy conservation while accounting for dissipative energy losses and star formation. The dissipative effects are evaluated from the initial gas fractions and from the orbital parameters via an "impulse" parameter, which characterizes the strength of the encounter. Given the progenitor properties, the model predicts the remnant stellar mass, half-mass radius, and velocity dispersion to an accuracy of 25%. The model is valid for both major and minor mergers. We provide an explicit recipe for semi-analytic models of galaxy formation.
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Papers by A. Dekel