Dependence on the environment of the abundance function of light-cone simulation dark matter haloes

TL;DR

This study investigates how the abundance of dark matter haloes varies with environment in a light-cone simulation, revealing significant differences based on halo isolation and a surprising upturn at higher redshifts.

Contribution

It introduces a phenomenological double power-law model for the halo abundance function that fits well across different environments, outperforming traditional theoretical mass functions.

Findings

Halo abundance varies significantly with halo isolation.

The Schechter function parameters decrease with increasing isolation.

An unexpected upturn in characteristic mass occurs at high redshift for isolated haloes.

Abstract

Aims.We study the dependence of the halo abundance function (AF) on different environments in a whole-sky $\Lambda$CDM light-cone halo catalogue extending to z < 0.65, using a simple and well-defined halo isolation criterion. Methods. The isolation status of each individual dark matter halo is determined by the distance to its nearest neighbour, which defines the maximum spherical region devoid of halos above a threshold mass around it (although the true size of such region may be much larger since it is not necessarily spherical). A versatile double power-law Schechter function is used to fit the dark matter halo AF, and its derived parameters are studied as a function of halo isolation status. Results. (a) Our function fits the halo abundances for all halo isolation statuses extremely well, while the well-established theoretical mass functions, integrated over the volume of the light-cone, provide an adequate but poorer fit than our phenomenological model. (b) As expected, and in agreement with other studies based on snap-shot simulations, we find significant differences of the halo abundance function as a function of halo isolation, indicating different rates of halo formation. The slope of the power law and the characteristic mass of the Schechter-like fitting function decrease with isolation, a result consistent with the formation of less massive haloes in lower density regions. (c) We find an unexpected upturn of the characteristic mass of the most isolated haloes of our sample. This upturn originates and characterises only the higher redshift regime (z > 0.45), which probably implies a significant and recent evolution of the isolation status of the most isolated and most massive haloes.