Why artificial disruption is not a concern for current cosmological simulations

TL;DR

This paper demonstrates that current cosmological simulations reliably resolve subhalo populations, showing that most disruptions are due to physical processes, not numerical artifacts, especially for recent accretions.

Contribution

It provides evidence that artificial disruption is negligible in modern simulations and clarifies the physical origins of subhalo disruption, especially for high-redshift sub-subhalos.

Findings

First-order subhalos after redshift 2 survive to present

Most disrupted subhalos are high-redshift sub-subhalos

High mass loss rates are confirmed as physical phenomena

Abstract

Recent studies suggest that cold dark matter subhalos are hard to disrupt and almost all cases of subhalo disruption observed in numerical simulations are due to numerical effects. However, these findings primarily relied on idealized numerical experiments, which do not fully capture the realistic conditions of subhalo evolution within a hierarchical cosmological context. Based on the Aquarius simulations, we identify clear segregation in the population of surviving and disrupted subhalos, which corresponds to two distinct acquisition channels of subhalos. We find that all of the first-order subhalos accreted after redshift 2 survive to the present time without suffering from artificial disruption. On the other hand, most of the disrupted subhalos are sub-subhalos accreted at high redshift. Unlike the first-order subhalos, sub-subhalos experience pre-processing and many of them are accreted through major mergers at high redshift, resulting in very high mass loss rates. We confirm these high mass loss rates are physical through both numerical experiments and semi-analytical modeling, thus supporting a physical origin for their rapid disappearance in the simulation. Even though we cannot verify whether these subhalos have fully disrupted or not, their extreme mass loss rates dictate that they can at most contribute a negligible fraction to the very low mass end of the subhalo mass function. We thus conclude that current state-of-the-art cosmological simulations have reliably resolved the subhalo population.