Halo Formation Redshift Research Articles

The manifestation of secondary bias on the galaxy population from IllustrisTNG300

ABSTRACT We use the improved IllustrisTNG300 magnetohydrodynamical cosmological simulation to revisit the effect that secondary halo bias has on the clustering of the central galaxy population. With a side length of 205 h−1 Mpc and significant improvements on the subgrid model with respect to previous Illustris simulations, IllustrisTNG300 allows us to explore the dependencies of galaxy clustering over a large cosmological volume and halo mass range. We show at high statistical significance that the halo assembly bias signal (i.e. the secondary dependence of halo bias on halo formation redshift) manifests itself on the clustering of the galaxy population when this is split by stellar mass, colour, specific star formation rate, and surface density. A significant signal is also found for galaxy size: at fixed halo mass, larger galaxies are more tightly clustered than smaller galaxies. This effect, in contrast to the rest of the dependencies, seems to be uncorrelated with halo formation time, with some small correlation only detected for halo spin. We also explore the transmission of the spin bias signal, i.e. the secondary dependence of halo bias on halo spin. Although galaxy spin retains little information about the total halo spin, the correlation is enough to produce a significant galaxy spin bias signal. We discuss possible ways to probe this effect with observations.

The Galaxy–Halo Connection in Low-mass Halos

Abstract Properties of galaxies vary systematically with the mass of their parent dark matter halos. This basic galaxy–halo connection shows a fair amount of scatter whose origin is not fully understood. Here, we study how differences in the halo assembly history affect central galaxies in low-mass (M halo < 1012 M ⊙) halos at z = 2–6 with the help of the MassiveFIRE suite of cosmological simulations. In contrast to previous works that tie galaxy properties to halo concentration and halo-formation redshift, we focus on halo growth rate as a measure of assembly history. We find that, at fixed halo mass, faster-growing halos tend to have lower stellar masses and higher star formation rates (SFRs) per unit stellar mass but similar overall SFRs. We provide a simple explanation for these findings with the help of an analytic model that captures approximately the behavior of our hydrodynamical simulations. Specifically, among halos of a given current mass, quickly growing halos have lower stellar masses (and thus higher specific SFRs) because they were less massive and had comparably lower cold-gas masses and SFRs in the past than slowly growing halos. By combining these findings with estimates for the scatter of the halo growth rate, we show that variations in growth rate at fixed halo mass may largely explain the scatter of the stellar mass–halo mass relation. In contrast, halo growth variations likely play only a minor role in the scatter of the star-forming sequence in low-mass galaxies.

ISW-galaxy cross correlation: a probe of dark energy clustering and distribution of dark matter tracers

Cross correlation of the Integrated Sachs-Wolfe signal (ISW) with the galaxy distribution in late time is a promising tool for constraining the dark energy properties. Here, we study the effect of dark energy clustering on the ISW-galaxy cross correlation and demonstrate the fact that the bias parameter between the distribution of the galaxies and the underlying dark matter introduces a degeneracy and complications. We argue that as the galaxy's host halo formation time is different from the observation time, we have to consider the evolution of the halo bias parameter. It will be shown that any deviation from ΛCDM model will change the evolution of the bias as well. Therefore, it is deduced that the halo bias depends strongly on the sub-sample of galaxies which is chosen for cross correlation and that the joint kernel of ISW effect and the galaxy distribution has a dominant effect on the observed signal. In this work, comparison is made specifically between the clustered dark energy models using two samples of galaxies. The first one is a sub-sample of galaxies from Sloan Digital Sky Survey, chosen with the r-band magnitude 18 < r < 21 and the dark matter halo host of mass M ∼1012M⊙ and formation redshift of zf ∼ 2.5. The second one is the sub-sample of Luminous Red galaxies with the dark matter halo hosts of mass M ∼ 1013M⊙ and formation redshift of zf ∼ 2.0. Using the evolved bias we improve the χ2 for the ΛCDM which reconciles the ∼1σ-2σ tension of the ISW-galaxy signal with ΛCDM prediction. Finally, we study the parameter estimation of a dark energy model with free parameters w0 and wa in the equation of state wde = w0 +waz/(1+z) with the constant bias parameter and also with an evolved bias model with free parameters of galaxy's host halo mass and the halo formation redshift.

Halo statistics analysis within medium volume cosmological N-body simulation

In this paper we present halo statistics analysis of a ?CDM N body cosmological simulation (from first halo formation until z = 0). We study mean major merger rate as a function of time, where for time we consider both per redshift and per Gyr dependence. For latter we find that it scales as the well known power law (1 + z)n for which we obtain n = 2.4. The halo mass function and halo growth function are derived and compared both with analytical and empirical fits. We analyse halo growth through out entire simulation, making it possible to continuously monitor evolution of halo number density within given mass ranges. The halo formation redshift is studied exploring possibility for a new simple preliminary analysis during the simulation run. Visualization of the simulation is portrayed as well. At redshifts z = 0?7 halos from simulation have good statistics for further analysis especially in mass range of 1011 ? 1014 M./h.

The dynamical state of dark matter haloes in cosmological simulations - I. Correlations with mass assembly history

Using a statistical sample of dark matter haloes drawn from a suite of cosmological N-body simulations of the Cold Dark Matter (CDM) model, we quantify the impact of a simulated halo's mass accretion and merging history on two commonly used measures of its dynamical state, the virial ratio eta and the centre of mass offset Delta r. Quantifying this relationship is important because the degree to which a halo is dynamically equilibrated will influence the reliability with which we can measure characteristic equilibrium properties of the structure and kinematics of a population of haloes. We begin by verifying that a halo's formation redshift zform correlates with its virial mass Mvir and we show that the fraction of its recently accreted mass and the likelihood of it having experienced a recent major merger increases with increasing Mvir and decreasing zform. We then show that both eta and Delta r increase with increasing Mvir and decreasing zform, which implies that massive recently formed haloes are more likely to be dynamically unrelaxed than their less massive and older counterparts. Our analysis shows that both eta and Delta r are good indicators of a halo's dynamical state, showing strong positive correlations with recent mass accretion and merging activity, but we argue that Delta r provides a more robust and better defined measure of dynamical state for use in cosmological N-body simulations at z~0. We find that Delta r < 0.04 is sufficient to pick out dynamically relaxed haloes at z=0. Finally, we assess our results in the context of previous studies, and consider their observational implications.

A marked correlation function analysis of halo formation times in the Millennium Simulation

We study the environmental dependence of the formation epoch of dark matter haloes in the Millennium Simulation: a ten billion particle N-body simulation of standard LambdaCDM cosmology. A sensitive test of this dependence - the marked correlation function - reveals highly significant evidence that haloes of a given mass form earlier in denser regions. We define a marked cross-correlation function, which helps quantify how this effect depends upon the choice of the halo population used to define the environment. The mean halo formation redshift as a function of the local overdensity in dark matter is also well determined, and we see an especially clear dependence for galaxy-sized haloes. This contradicts one of the basic predictions of the excursion set model of structure formation, even though we see that this theory predicts other features of the distribution of halo formation epochs rather well. It also invalidates an assumption usually employed in the popular halo, or HOD, models of galaxy clustering, namely that the distribution of halo properties is a function of halo mass but not of halo environment.

The subhalo populations of ΛCDM dark haloes

We investigate the subhalo populations of dark matter haloes in the concordance Λ cold dark matter (ΛCDM) cosmology. We use a large cosmological simulation and a variety of high-resolution resimulations of individual cluster and galaxy haloes to study the systematics of subhalo populations over ranges of 1000 in halo mass and 1000 in the ratio of subhalo to parent halo mass. The subhalo populations of different haloes are not scaled copies of each other, but vary systematically with halo properties. On average, the amount of substructure increases with halo mass. At fixed mass, it decreases with halo concentration and with halo formation redshift. These trends are comparable in size to the scatter in subhalo abundance between similar haloes. Averaged over all haloes of given mass, the abundance of low-mass subhaloes per unit parent halo mass is independent of parent mass. It is very similar to the abundance per unit mass of low-mass haloes in the Universe as a whole, once differing boundary definitions for subhaloes and haloes are accounted for. The radial distribution of subhaloes within their parent haloes is substantially less centrally concentrated than that of the dark matter. It varies at most weakly with the mass (or concentration) of the parent halo and not at all with subhalo mass. It does depend on the criteria used to define the subhalo population considered. About 90 per cent of present-day subhaloes were accreted after z= 1 and about 70 per cent after z= 0.5. Only about 8 per cent of the total mass of all haloes accreted at z= 1 survives as bound subhaloes at z= 0. For haloes accreted at z= 2, the survival mass fraction is just 2 per cent. Subhaloes seen near the centre of their parent typically were accreted earlier and retain less of their original mass than those seen near the edge. These strong systematics mean that comparison with galaxies in real clusters is only possible if the formation of the luminous component is modelled appropriately.

On galaxy cluster sizes and temperatures

We show that the distribution of the sizes and temperatures of clusters can be used to constrain cosmological models. The size–temperature (ST) distribution predicted in a flat Gaussian cluster-abundance-normalized model agrees well with the fairly tight ST relation observed. A larger power-spectrum amplitude σ8 would give rise to a larger scatter about the ST relation as would a larger value of Ω0 and/or long non-Gaussian high-density tails in the probability density function. For Gaussian initial conditions, the ST distribution suggests a constraint The ST relation is expected to get tighter at high redshifts. In the process, we derive a simple formula for the halo formation–redshift distribution for non-Gaussian models. We also suggest that the discrepancy between the naive zero-redshift ST relation and that observed may be owing, at least in part, to the fact that lower-mass clusters form over a wider range of redshifts. An Appendix derives an equation for the formation–redshift distribution of haloes.