Universal Substructure Distributions in LCDM halos: Can we find a Fossil Group?

TL;DR

This study uses cosmological simulations to analyze subhalo populations in galaxy groups, investigating if early-forming halos can explain fossil groups, and finds that substructure suppression is insufficient to match observations.

Contribution

It provides new insights into the substructure distribution in LCDM halos and assesses the viability of fossil groups as early-forming systems with reduced substructure.

Findings

Maximum subhalo suppression is a factor of 2-2.5, less than the factor of 6 needed.

Substructure velocity function slope is independent of formation time.

Self-similarity in subhalo populations persists across galaxy and cluster scales.

Abstract

We use large cosmological N-body simulations to study the subhalo population in galaxy group sized halos. In particular, we look for fossil group candidates with typical masses ~10-25% of Virgo cluster but with an order of magnitude less substructure. We examine recent claims that the earliest systems to form are deficient enough in substructure to explain the luminosity function found in fossil groups. Although our simulations show a correlation between the halo formation time and the number of subhalos, the maximum suppression of subhalos is a factor of 2-2.5, whereas a factor of 6 is required to match fossil groups and galaxies. While the number of subhalos depends weakly on the formation time, the slope of the halo substructure velocity function does not. The satellite population within Cold Dark Matter (CDM) halos is self-similar at scales between galaxies and galaxy clusters regardless of mass, whereas current observations show a break in self-similarity at a mass scale corresponding to group of galaxies.