15223533
Galaxy Evolution from Halo Occupation Distribution Modeling of DEEP2 and SDSS Galaxy Clustering
We model the luminosity-dependent projected two-point correlation function of DEEP2 (z ~ 1) and SDSS (z ~ 0) galaxies within the HOD framework. At both epochs, there is a tight correlation between central galaxy luminosity and halo mass, with the slope and scatter decreasing for larger halo masses, and the fraction of satellite galaxies decreases at higher luminosity. We find little evolution in the relation between mass scales of host halos for central galaxies and satellite galaxies above the same luminosity threshold. Combining these HOD results with theoretical predictions of the typical growth of halos, we establish an evolutionary connection between the galaxy populations at the two redshifts by linking z ~ 0 central galaxies to z ~ 1 central galaxies that reside in their progenitor halos. We find that the stellar mass growth of galaxies depends on halo mass. On average, the majority of the stellar mass in central galaxies residing in z ~ 0 low-mass halos (~5 × 1011 h-1 M☉) and only a small fraction of the stellar mass in central galaxies of high-mass halos (~1013 h-1 M☉) result from star formation between z ~ 1 and z ~ 0. In addition, the mass scale of halos where the star formation efficiency reaches a maximum is found to shift toward lower mass with time. Future work that combines HOD modeling of the clustering of galaxies at different redshifts with the assembly history and dynamical evolution of dark matter halos can lead to an understanding of the stellar mass growth due to both mergers and star formation as a function of host halo mass and provide powerful tests of galaxy formation theories.
119091917
On the Mass-to-Light Ratio of Large-Scale Structure
We examine the dependence of the mass-to-light (M/L) ratio of large-scale structure on cosmological parameters, in models that are constrained to match observations of the projected galaxy correlation function wp(rp) and the galaxy luminosity function. For a sequence of cosmological models with a fixed, observationally motivated power spectrum shape and increasing normalization σ8, we find parameters of the galaxy halo occupation distribution (HOD) that reproduce wp(rp) measurements as a function of luminosity from the Sloan Digital Sky Survey (SDSS). From these HOD models we calculate the r-band conditional luminosity function Φ(L|Mh), and from this the mean M/L ratio as a function of halo mass Mh. We also use Φ(L|Mh) to populate halos of N-body simulations with galaxies and thereby compute M/L in a range of large-scale environments, including cluster infall regions. For all cosmological models, the M/L ratio in high-mass halos or high-density regions is approximately independent of halo mass or smoothing scale. However, the "plateau" value of M/L depends on σ8 in addition to the obvious proportionality with the matter density parameter Ωm, and it represents the universal value M/L = Ωmρcrit/ρlum only for models in which the galaxy correlation function is approximately unbiased, i.e., with σ8 ≈ σ8g. Our results for cluster mass halos follow the trend (M/L)cl = 577(Ωm/0.3)(σ8/0.9)1.7 h M☉/L☉. Combined with the mean M/L ratio for CNOC galaxy clusters, this relation implies (σ8/0.9)(Ωm/0.3)0.6 = 0.75 ± 0.06. M/L estimates for SDSS clusters and the virial regions of clusters in the CAIRNS survey imply a similar value of σ8Ω, while the CAIRNS estimates for cluster infall regions imply a lower value. These results are inconsistent with parameter values Ωm ≈ 0.3, σ8 ≈ 0.9 favored by recent joint analyses of cosmic microwave background measurements and other large-scale structure data, although they agree with values inferred from the van den Bosch et al. analysis of the 2dF Galaxy Redshift Survey. We discuss possible resolutions of this discrepancy, none of which seems entirely satisfactory. In appendices we present an improved formula for halo bias factors calibrated on our 3603 N-body simulations and an improved analytic technique for calculating the galaxy correlation function from a given cosmological model and HOD.
14026331
Redshift-space distortions with the halo occupation distribution – I. Numerical simulations
We show how redshift-space distortions of the galaxy correlation function or power spectrum can constrain the matter density parameter Ω m and the linear matter fluctuation amplitude σ 8 . We improve on previous treatments by adopting a fully non-linear description of galaxy clustering and bias, which allows us to achieve the accuracy demanded by larger galaxy redshift surveys and to break parameter degeneracies by combining large-scale and small-scale distortions. Given an observationally motivated choice of the initial power spectrum shape, we consider different combinations of Ω m and σ 8 and find parameters of the galaxy halo occupation distribution (HOD) that yield nearly identical galaxy correlation functions in real space. We use these HOD parameters to populate the dark matter haloes of large N-body simulations, from which we measure redshift-space distortions on small and large scales. We include a velocity bias parameter α v that allows the velocity dispersions of satellite galaxies in haloes to be systematically higher or lower than those of dark matter. Large-scale distortions are determined by the parameter combination β ≡ Ω 0.6 m /b g , where bg is the bias factor defined by the ratio of galaxy and matter correlation functions, in agreement with the linear theory prediction of parameter degeneracy. However, linear theory does not accurately describe the distortions themselves on scales accessible to our simulations. We provide fitting formulas to estimate β from measurements of the redshift-space correlation function or power spectrum, and we show that these formulas are significantly more accurate than those in the existing literature. On small scales, the 'FOG' distortions at projected separations ∼0.1 h -1 Mpc depend on Ω m α 2 v but are independent of as, while at intermediate separations they depend on σ 8 as well. One can thus use measurements of redshift-space distortions over a wide range of scales to separately determine Ω m , σ 8 , and α v .
117560042
A z ∼ 5.7 Lyα EMISSION LINE WITH AN ULTRABROAD RED WING
Using the Ly? emission line as a tracer of high-redshift, star-forming galaxies, hundreds of Ly? emission line galaxies (LAEs) at z > 5 have been detected. These LAEs are considered to be low-mass young galaxies, critical to the re-ionization of the universe and the metal enrichment of the circumgalactic medium (CGM) and the intergalactic medium (IGM). It is assumed that outflows in LAEs can help both ionizing photons and Ly? photons escape from galaxies. However, we still know little about the outflows in high-redshift LAEs due to observational difficulties, especially at redshift >5. Models of Ly? radiative transfer predict asymmetric Ly? line profiles with broad red wings in LAEs with outflows. Here, we report a z ~ 5.7 Ly? emission line with a broad red wing extending to >1000?km s?1 relative to the peak of Ly? line, which has been detected in only a couple of z > 5 LAEs until now. If the broad red wing is ascribed to gas outflow instead of active galactic nucleus activity, the outflow velocity could be larger than the escape velocity (~500?km s?1) of a typical halo mass of z ~ 5.7 LAEs, which is consistent with the idea that outflows in LAEs disperse metals to CGM and IGM.