Correlation between Outlying Halo Abundance and Host Halo Properties

TL;DR

This study investigates how properties of host dark matter halos influence the abundance of neighboring halos outside the virial radius, revealing correlations that extend beyond traditional boundaries and depend on halo assembly bias.

Contribution

It is the first to quantify the variation in outlying halo occupation beyond the virial radius and explores how host properties relate to neighboring halo abundance at large distances.

Findings

Host halo properties affect neighboring halo abundance beyond the virial radius.

Correlation peaks do not align with the virial or splashback radius.

Outlying halo occupation relates to halo assembly bias.

Abstract

The correlations between dark matter halo properties and subhalo abundance, or occupation, have been studied extensively; however, existing studies have mainly focused on subhalos within the virial radius of the host halo. In this work, we quantify the correlation between host halo properties and the abundance of neighboring halos that reside right outside of the virial radius of the host halos. We compute the correlations between four host halo properties (half-mass scale, concentration, peak-mass scale, and spin) and the outlying halo occupation out to 1.5 Mpc for Milky Way-mass host halos, and study how the correlation strength varies with radius. We also investigate if the outlying halo occupation can provide information about the host halo properties. We find that host halo properties impact the neighboring halo abundance beyond the virial radius, and the locations at which the correlation peaks do not typically align with the virial radius or splashback radius. The behavior of this observed correlation as a function of radius, especially in the outskirts, is connected to the effect of halo assembly bias. However, there is no universal behavior when considering different host halo properties. Our results are the first to quantify the occupation variation of outlying halos beyond the virial radius. They provide the theoretical background for interpreting the observed satellite systems when the observed satellites are not strictly defined to be within the virial radius.