The Dependence of Subhalo Abundance on Halo Concentration

TL;DR

This paper presents a model predicting subhalo abundance based on halo mass and concentration, highlighting the impact of formation history on subhalo counts and implications for understanding halo assembly bias.

Contribution

The paper introduces a new model that incorporates halo concentration to accurately predict subhalo abundance and its scatter, improving upon previous models.

Findings

Model successfully reproduces mean and scatter of subhalo occupation.

Correlation between subhalo abundance and halo concentration impacts inferences about halo properties.

Future surveys can test halo assembly bias through satellite occupation measurements.

Abstract

Hierarchical structure formation implies that the number of subhalos within a dark matter halo depends not only on halo mass, but also on the formation history of the halo. This dependence on the formation history, which is highly correlated with halo concentration, can account for the super-Poissonian scatter in subhalo occupation at a fixed halo mass that has been previously measured in simulations. Here we propose a model to predict the subhalo abundance function for individual host halos, that incorporates both halo mass and concentration. We combine results of cosmological simulations with a new suite of zoom-in simulations of Milky Way-mass halos to calibrate our model. We show the model can successfully reproduce the mean and the scatter of subhalo occupation in these simulations. The implications of this correlation between subhalo abundance and halo concentration are further investigated. We also discuss cases in which inferences about halo properties can be affected if this correlation between subhalo abundance and halo concentration is ignored; in these cases our model would give a more accurate inference. We propose that with future deep surveys, satellite occupation in the low-mass regime can be used to verify the existence of halo assembly bias.