Variation of the subhalo abundance in dark matter halos

TL;DR

This study investigates the variation in subhalo abundance within dark matter halos using high-resolution cosmological simulations, revealing correlations with formation history and halo concentration.

Contribution

It provides the first detailed statistical analysis of subhalo abundance variations in galaxy-sized halos from high-resolution simulations.

Findings

Subhalo abundance varies significantly between halos.

Earlier formed halos tend to have fewer subhalos.

Subhalo abundance correlates with halo concentration and formation time.

Abstract

We analyzed the statistics of subhalo abundance of galaxy-sized and giant-galaxy-sized halos formed in a high-resolution cosmological simulation of a 46.5Mpc cube with the uniform mass resolution of $10^6 M_{\odot}$. We analyzed all halos with mass more than $1.5 \times 10^{12}M_{\odot}$ formed in this simulation box. The total number of halos was 125. We found that the subhalo abundance, measured by the number of subhalos with maximum rotation velocity larger than 10% of that of the parent halo, shows large halo-to-halo variations. The results of recent ultra-high-resolution runs fall within the variation of our samples. We found that the concentration parameter and the radius at the moment of the maximum expansion shows fairly tight correlation with the subhalo abundance. This correlation suggests that the variation of the subhalo abundance is at least partly due to the difference in the formation history. Halos formed earlier have smaller number of subhalos at present.