The Fate of Substructures in Cold Dark Matter Haloes

TL;DR

This study uses the Millennium Simulation to analyze the properties, distributions, and merger behaviors of substructures within dark matter haloes, revealing mass-dependent patterns and implications for galaxy formation models.

Contribution

It provides new insights into the mass function, spatial distribution, and merger dynamics of subhaloes in a LambdaCDM universe, based on high-resolution simulation data.

Findings

Subhalo mass function deviates from a power law at high masses.

High mass subhaloes are less radially concentrated and have different angular distributions.

Subhalo mergers are more likely between pre-associated structures and depend on subhalo mass.

Abstract

We use the Millennium Simulation, a large, high resolution N-body simulation of the evolution of structure in a LambdaCDM cosmology, to study the properties and fate of substructures within a large sample of dark matter haloes. We find that the subhalo mass function departs significantly from a power law at the high mass end. We also find that the radial and angular distributions of substructures depend on subhalo mass. In particular, high mass subhaloes tend to be less radially concentrated and to have angular distributions closer to the direction perpendicular to the spin of the host halo than their less massive counterparts. We find that mergers between subhaloes occur. These tend to be between substructures that were already dynamically associated before accretion into the main halo. For subhaloes larger than 0.001 times the mass of the host halo, it is more likely that the subhalo will merge with the central or main subhalo than with another subhalo larger than itself. For lower masses, subhalo-subhalo mergers become equally likely to mergers with the main subhalo. Our results have implications for the variation of galaxy properties with environment and for the treatment of mergers in galaxy formation models.