Universal subhalo accretion in cold and warm dark matter cosmologies

TL;DR

This study investigates how low-mass halos are accreted in cold and warm dark matter cosmologies, revealing a universal preferential infall along the axis of weakest collapse, with WDM showing more beamed accretion.

Contribution

It demonstrates that the infall pattern of subhalos is universally aligned with the shear tensor's weakest axis across different dark matter models, highlighting differences between CDM and WDM.

Findings

Subhalos are preferentially accreted along the shear tensor's weakest axis.

The beaming strength varies with mass and redshift, being stronger for massive halos at high redshift.

WDM exhibits more strongly beamed accretion than CDM across all redshifts.

Abstract

The influence of the large scale structure on host halos may be studied by examining the angular infall pattern of subhalos. In particular, since warm and cold dark matter cosmologies predict different abundances and internal properties for halos at the low mass end of the mass function, it is interesting to examine if there are differences in how these low mass halos are accreted. The accretion events are defined as the moment a halo becomes a substructure, namely when it crosses its host's virial radius. We quantify the cosmic web at each point by the shear tensor and examine where, with respect to its eigenvectors, such accretion events occur in cold ($\Lambda$CDM) and warm (1keV sterile neutrino WDM) dark matter cosmological models. We find that the CDM and WDM subhalos are preferentially accreted along the principal axis of the shear tensor corresponding to the direction of weakest collapse. The beaming strength is modulated by the host and subhalo masses and by the redshift at which the accretion event occurs. Although strongest for the most massive hosts and subhalos at high redshift, the preferential infall is found to be always aligned with the axis of weakest collapse, thus we say that it has universal nature. We compare the strength of beaming in the WDM cosmology with the one found in the $\Lambda$CDM scenario. While the main findings remain the same, the accretion in the WDM model for the most massive host halos appears more beamed than in $\Lambda$CDM cosmology across all the redshifts.