Dark matter halo abundances, clustering and assembly histories at high redshift

TL;DR

This study uses high-resolution simulations to analyze the properties, abundance, and clustering of massive high-redshift halos, revealing their rapid growth, merger activity, and implications for cosmic reionization.

Contribution

It provides detailed insights into high-mass halo properties, their assembly histories, and the impact of mergers on photon production at high redshift, comparing results with the extended Press-Schechter model.

Findings

Halo abundance depends on mass definition.

Many massive halos undergo rapid mass accretion.

Merger activity influences photon production and reionization.

Abstract

We use a suite of high-resolution N-body simulations to study the properties, abundance and clustering of high mass halos at high redshift, including their mass assembly histories and mergers. We find that the analytic form which best fits the abundance of halos depends sensitively on the assumed definition of halo mass, with common definitions of halo mass differing by a factor of two for these low concentration, massive halos. A significant number of massive halos are undergoing rapid mass accretion, with major merger activity being common. We compare the mergers and mass accretion histories to the extended Press-Schechter formalism. We consider how major merger induced star formation or black hole accretion may change the distribution of photon production from collapsed halos, and hence reionization, using some simplified examples. In all of these, the photon distribution for a halo of a given mass acquires a large scatter. If rare, high mass halos contribute significantly to the photon production rates, the scatter in photon production rate can translate into additional scatter in the sizes of ionized bubbles.