Non-linear stochastic galaxy biasing in cosmological simulations

Abstract

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−1 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 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 compared with 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.

GaBoDS: The Garching‐Bonn Deep Survey

“…An anti-bias on the scales considered here and a characteristic "dip" in the functional form of the bias factor is in concordance with recent numerical simulations of dark matter structure formation (Springel et al 2005;Weinberg et al 2004;Guzik & Seljak 2001;Pearce et al 2001;Yoshikawa et al 2001;Somerville et al 2001;Jenkins et al 1998). The scaledependence is due to the fact that the galaxy clustering is a power-law over a wide range of scales, reflected by N 2 in Fig.…”

Light on Dark Matter

“…Semi-analytic models that follow the transformation of gas into stars lead to similar expectations (Blanton et al 1999;Somerville et al 2001;Ostriker et al 2003). These same results are found directly in observations.…”

The Broadband Optical Properties of Galaxies with Redshifts 0.02 < z < 0.22

“…As a first step in understanding the joint distribution of galaxy properties, we present here a study of the number density and luminosity density distributions of galaxy colors, profiles, luminosities, surface brightnesses, and local densities. Our purpose is to measure properties related to quantities that cosmological gasdynamical simulations (Nagamine et al 2001;Pearce et al 2001;Steinmetz & Navarro 2002) or semianalytic models (Somerville et al 2001;Mathis et al 2002) can predict or will soon be able to predict, such as galaxy ages, sizes, stellar masses, and degrees of concentration.…”