An Accurate Comprehensive Approach to Substructure: III. Masses and Formation Times of the Host Haloes

TL;DR

This paper completes a comprehensive analysis of dark matter substructure, focusing on masses and formation times of host haloes, revealing how subhalo properties relate to halo assembly history and merger events.

Contribution

It extends previous work by analyzing substructure in haloes with major mergers, linking subhalo mass functions and distributions to halo formation and merger history.

Findings

Subhalo mass function depends on halo concentration.

Radial distribution of subhaloes relates to last major merger time.

Subhalo properties encode halo formation history.

Abstract

With this Paper we complete a comprehensive study of substructure in dark matter haloes. In Paper I we derived the radial distribution and mass function (MF) of accreted subhaloes (scaled to the radius and mass of the host halo) and showed they are essentially universal. This is not the case, however, for those of stripped subhaloes, which depend on halo mass and assembly history. In Paper II we derived these latter properties in the simplest case of purely accreting haloes. Here we extend the study to ordinary haloes having suffered major mergers. After showing that all the properties of substructure are encoded in the mean truncated-to-original subhalo mass ratio profile, we demonstrate that the dependence of the subhalo MF on halo mass arises from their mass-dependent concentration, while the shape of the subhalo radial distribution depends on the time of the last major merger of the host halo. In this sense, the latter property is a better probe of halo formation time than the former. Unfortunately, this is not the case for the radial distribution of satellites as this profile is essentially disconnected from subhalo stripping and the properties of accreted subhaloes are independent of the halo formation time.