On the distribution of haloes, galaxies and mass
Abstract
The stochasticity in the distribution of dark haloes in the cosmic density field is reflected in the distribution function P_{V}(N_{h}δ_{m}), which gives the probability of finding N_{h} haloes in a volume V with mass density contrast δ_{m}. We study the properties of this function using highresolution Nbody simulations, and find that P_{V}(N_{h}δ_{m}) is significantly nonPoisson. The ratio between the variance and the mean goes from ~1 (Poisson) at 1+δ_{m}<<1 to <1 (subPoisson) at 1+δ_{m}~1 to >1 (superPoisson) at 1+δ_{m}>>1. The mean bias relation is found to be well described by halo bias models based on the PressSchechter formalism. The subPoisson variance can be explained as a result of halo exclusion, while the superPoisson variance at high δ_{m} may be explained as a result of halo clustering. A simple phenomenological model is proposed to describe the behaviour of the variance as a function of δ_{m}. Galaxy distribution in the cosmic density field predicted by semianalytic models of galaxy formation shows similar stochastic behaviour. We discuss the implications of the stochasticity in halo bias to the modelling of higher order moments of dark haloes and of galaxies.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 July 2002
 DOI:
 10.1046/j.13658711.2002.05378.x
 arXiv:
 arXiv:astroph/0105008
 Bibcode:
 2002MNRAS.333..730C
 Keywords:

 galaxies: clusters: general;
 galaxies: formation;
 cosmology: theory;
 dark matter;
 Astrophysics
 EPrint:
 10 pages, 6 figures, Latex using MN2e style. Minor changes. Accepted for publication in MNRAS