The Intergalactic Stellar Population From Mergers of Elliptical Galaxies With Dark Matter Halos (original) (raw)
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Astrophysical Journal, 2007
We use a set of simulation-based models for the dissipationless evolution of galaxies since z=1 to constrain the fate of accreted satellites embedded in dark matter subhalos. These models assign stellar mass to dark matter halos at z=1 by relating the observed galaxy stellar mass function (GSMF) to the halo+subhalo mass function monotonically. The evolution of the stellar mass content is then followed using halo merger trees extracted from N-body simulations. Our models are differentiated only in the fate assigned to satellite galaxies once subhalos, within which satellites are embedded, disrupt. These models are confronted with the observed evolution in the massive end of the GSMF, the z~0 brightest cluster galaxy (BCG)-cluster mass relation, and the combined BCG and intracluster light (ICL) luminosity distribution -- all observables expected to evolve approximately dissipationlessly since z=1. The combined observational constraints favor a model in which the vast majority (>80%) of satellite stars from disrupted subhalos go into the ICL. Conversely, models that leave behind a significant population of satellite galaxies once the subhalo has disrupted are strongly disfavored, as are models that put a significant fraction of satellite stars into the BCG. Our results show that observations of the ICL provide useful and unique constraints on models of galaxy merging and the dissipationless evolution of galaxies in groups and clusters.
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Monthly Notices of the Royal Astronomical Society, 2006
Cosmological (ΛCDM) TreeSPH simulations of the formation and evolution of twelve galaxy groups of virial mass ∼10 14 M ⊙ have been performed. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metallicity dependent radiative cooling, strong star-burst driven galactic super-winds and effects of a meta-galactic UV field. The intra-group (IG) stars are found to contribute 12-45% of the total group B-band luminosity at z=0. The lowest fractions are found for groups with only a small difference between the R-band magnitudes of the first and second ranked group galaxy (∆m 12,R < ∼ 0.5), the larger fractions are typical of "fossil" groups (FGs, ∆m 12,R ≥2). A similar conclusion is obtained from BVRIJK surface brightness profiles of the IG star populations. The IG stars in the 4 FGs are found to be older than the ones in the 8 "normal" groups (nonFGs), on average by about 0.3-0.5 Gyr. The typical colour of the IG stellar population is B-R=1.4-1.5, for both types of systems in good agreement with observations. The mean Iron abundance of the IG stars is slightly sub-solar in the central part of the groups (r ∼100 kpc) decreasing to about 40% solar at about half the virial radius. The IG stars are α-element enhanced with a trend of [O/Fe] increasing with r and an overall [O/Fe]∼0.45 dex, indicative of dominant enrichment from type II supernovae. The abundance properties are similar for both types of systems. The velocity distributions of the IG stars are, at r > ∼ 30 kpc, significantly more radially anisotropic for FGs than for the nonFGs; this also holds for the velocity distributions of the group galaxies. This indicates that an important characteristic determining whether a group becomes fossil or not, apart from its formation time, as discussed by D'Onghia et al., is the "initial" velocity distribution of the group galaxies. For FGs one can dynamically infer the (dark matter dominated) mass distribution of the groups all the way to the virial radius, from the kinematics of the IG stars or group galaxies. For the nonFGs this method overestimates the group mass at r > ∼ 200 kpc, by up to a factor of two at the virial radius. This is interpreted as FGs being, in general, more relaxed than nonFGs. Finally, FGs of the above virial mass should host ∼500 planetary nebulae at projected distances between 100 and 1000 kpc from the first ranked galaxy. All results obtained appear consistent with the tidal stripping and merging scenario for the formation of FGs, put forward by D'Onghia et al.
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Monthly Notices of the Royal Astronomical Society, 2006
We use numerical simulations to investigate the origin and structure of the luminous halos that surround isolated galaxies. These stellar structures extend out to several hundred kpc away from a galaxy, and consist of stars shed by merging subunits during the many accretion events that characterize the hierarchical assembly of galaxies. Such origin suggests that outer luminous halos are ubiquitous and that they should appear as an excess of light over extrapolations of the galaxy's inner profile beyond its traditional luminous radius. The mass profile of the accreted stellar component is well approximated by a model where the logarithmic slope steepens monotonically with radius; from ρ ∝ r −3 at the luminous edge of the galaxy to r −4 or steeper near the virial radius of the system. Such spatial distribution is consistent with that of Galactic and M31 globular clusters, suggesting that many of the globulars were brought in by accretion events, in a manner akin to the classic Searle-Zinn scenario. Luminous halos are similar in shape to their dark matter counterparts, which are only mildly triaxial and much rounder than dark halos formed in simulations that do not include a dissipative luminous component. The outer stellar spheroid is supported by a velocity dispersion tensor with a substantial and radially increasing radial anisotropy; from σ 2 r /σ 2 t ∼ 2 at the edge of the central galaxy to ∼ 5 at the virial radius. These properties distinguish the stellar halo from the dark matter component, which is more isotropic in velocity space, as well as from some tracers of the outer spheroid such as satellite galaxies. Most stars in the outer halo formed in progenitors that have since merged with the central galaxy; very few stars in the halo are contributed by satellites that survive as self-bound entities at the present. These features are in reasonable agreement with recent observations of the outer halo of the Milky Way, of M31, and of other isolated spirals, and suggest that all of these systems underwent an early period of active merging, as envisioned in hierarchical models of galaxy formation.
Stars beyond Galaxies: The Origin of Extended Luminous Halos around Galaxies
Mon Notic Roy Astron Soc, 2005
(Abridged) We use numerical simulations to investigate the origin and structure of the luminous halos that surround isolated galaxies. These stellar structures extend out to several hundred kpc away from a galaxy, and consist of stars shed by merging subunits during the many accretion events that characterize the hierarchical assembly of galaxies. Such origin suggests that outer luminous halos are ubiquitous and that they should appear as an excess of light over extrapolations of the galaxy's inner profile beyond its traditional luminous radius. The mass profile of the accreted stellar component is well approximated by a model where the logarithmic slope steepens monotonically with radius; from -3 at the luminous edge of the galaxy to -4 or steeper near the virial radius of the system. Such spatial distribution is consistent with that of Galactic and M31 globular clusters, suggesting that many of the globulars were brought in by accretion events, in a manner akin to the classic Searle-Zinn scenario. The outer stellar spheroid is supported by a velocity dispersion tensor with a substantial and radially increasing radial anisotropy. These properties distinguish the stellar halo from the dark matter component, which is more isotropic in velocity space, as well as from some tracers of the outer spheroid such as satellite galaxies. Most stars in the outer halo formed in progenitors that have since merged with the central galaxy; very few stars in the halo are contributed by satellites that survive as self-bound entities at the present. These features are in reasonable agreement with recent observations of the outer halo of the MW, of M31, and of other isolated spirals, and suggest that all of these systems underwent an early period of active merging, as envisioned in hierarchical models of galaxy formation.
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.
Intergalactic stellar populations in intermediate redshift clusters
Monthly Notices of the Royal Astronomical Society, 2012
A substantial fraction of the total stellar mass in rich clusters of galaxies resides in a diffuse intergalactic component usually referred to as the Intra-Cluster Light (ICL). Theoretical models indicate that these intergalactic stars originate mostly from the tidal interaction of the cluster galaxies during the assembly history of the cluster, and that a significant fraction of these stars could have formed in-situ from the late infall of cold metal-poor gas clouds onto the cluster. However, these models also over-predict the fraction of stellar mass in the ICL by a substantial margin, something that is still not well understood. The models also make predictions about the age distribution of the ICL stars, which may provide additional observational constraints. Here we present population synthesis models for the ICL of an intermediate redshift (z=0.29) X-ray cluster that we have extensively studied in previous papers. The advantage of observing intermediate redshift clusters rather than nearby ones is that the former fit the field of view of multi-object spectrographs in 8m telescopes and therefore permit to encompass most of the ICL with only a few well placed slits.
Monthly Notices of the Royal Astronomical Society, 2007
We study the origin of the diffuse stellar component (DSC) in 117 galaxy clusters extracted from a cosmological hydrodynamical simulation. We identify all galaxies present in the simulated clusters at 17 output redshifts, starting with z = 3.5, and then build the family trees for all the z = 0 cluster galaxies. The most massive cluster galaxies show complex family trees, resembling the merger trees of dark matter halos, while the majority of other cluster galaxies experience only one or two major mergers during their entire life history. Then for each diffuse star particle identified at z = 0, we look for the galaxy to which it once belonged at an earlier redshift, thus linking the presence of the diffuse stellar component to the galaxy formation history.
The evolution of the galaxy star formation activity in massive haloes
Astronomy & Astrophysics, 2014
Context. There is now a large consensus that the current epoch of the Cosmic Star Formation History (CSFH) is dominated by low mass galaxies while the most active phase, between redshift 1 and 2, is dominated by more massive galaxies, which undergo a faster evolution. Aims. Massive galaxies tend to inhabit very massive halos such as galaxy groups and clusters. We aim to understand whether the observed "galaxy downsizing" could be interpreted as a "halo downsizing", whereas the most massive halos, and their galaxy populations, evolve more rapidly than the halos of lower mass. Methods. We study the contribution to the CSFH of galaxies inhabiting group-sized halos. This is done through the study of the evolution of the Infra-Red (IR) luminosity function of group galaxies from redshift 0 to redshift ∼ 1.6. We use a sample of 39 X-ray selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid-and far-IR surveys have been conducted with Spitzer MIPS and with the Photodetector Array Camera and Spectrometer (PACS) on board of the Herschel satellite.