The Clustering and Host Halos of Galaxy Mergers at High Redshift

TL;DR

This study uses high-resolution cosmological simulations to analyze the clustering behavior of galaxy-hosting dark matter subhalos after mergers at high redshift, revealing transient clustering enhancements and their dependence on mass and environment.

Contribution

It provides new insights into the small-scale clustering of recently merged subhalos and how this relates to their host halo properties and merger history at high redshift.

Findings

Merged subhalos show enhanced clustering on 100-300 kpc/h scales shortly after merger.

The clustering enhancement is more pronounced for massive subhalos and their hosts.

Subhalo merger fraction is independent of halo mass within the studied scales.

Abstract

High-resolution simulations of cosmological structure formation indicate that dark matter substructure in dense environments, like groups and clusters, may survive for a long time. These dark matter subhalos are the likely hosts of galaxies. We examine the small-scale spatial clustering of subhalo major mergers at high redshift using high-resolution N-body simulations of cosmological volumes. Recently merged, massive subhalos exhibit enhanced clustering on scales ~100-300 kpc/h, relative to all subhalos of the same infall mass, for a short time after a major merger (< 500 Myr). The small-scale clustering enhancement is smaller for lower mass subhalos, which also show a deficit on scales just beyond the excess. Halos hosting recent subhalo mergers tend to have more subhalos; for massive subhalos the excess is stronger and it tends to increase for the most massive host halos. The subhalo merger fraction is independent of halo mass for the scales we probe. In terms of satellite and central subhalos, the merger increase in small-scale clustering for massive subhalos arises from recently merged massive central subhalos having an enhanced satellite population. Our mergers are defined via their parent infall mass ratios. Subhalos experiencing major mass gains also exhibit a small-scale clustering enhancement, but these correspond to two-body interactions leading to two final subhalos, rather than subhalo coalescence.