Halo correlations in nonlinear cosmic density fields

TL;DR

This paper investigates the correlation properties of dark matter halos in nonlinear cosmic density fields, deriving how their hierarchical clustering patterns depend on internal properties and gravitational dynamics.

Contribution

It introduces a model assuming matter correlation functions as products of two-body functions, deriving halo correlation properties and explicit formulas for halo count distributions.

Findings

Hierarchical pattern of matter correlations is conserved in halos.

Halo correlations depend only on internal parameter x=m/r^(3-gamma).

Higher masses are favored within clusters due to gravitational bias.

Abstract

The question we address in this paper is the determination of the correlation properties of the dark matter halos appearing in cosmic density fields once they underwent a strongly nonlinear evolution induced by gravitational dynamics. Assuming that the high-order correlation functions of the matter field behave as products of two-body correlation functions, we derive the correlation properties of the halos, that are assumed to represent the correlation properties of galaxies or clusters. The hierarchical pattern originally induced by gravity is shown to be conserved for the halos. The strength of their correlations at any order varies, however, but is found to depend only on their internal properties, namely on the parameter x=m/r^(3-gamma) where m is the mass of the halo, r its size and gammma is the power law index of the two-body correlation function. We were able to derive the explicit form of the generating function of the moments of the halo count probability distribution function. In particular we show explicitely that, generically, S_p(x) -> p^(p-2) in the rare halo limit. Various illustrations of our general results are presented. As a function of the properties of the underlying matter field, we construct the count probabilities for halos and in particular discuss the halo void probability. We also evaluate the dependence of the halo mass function on the environment. We found that within clusters, hierarchical clustering implies the higher masses are favored. We stress that this bias is naturally induced by gravity.