The Three Hundred Project: Substructure in hydrodynamical and dark matter simulations of galaxy groups around clusters

TL;DR

This study compares hydrodynamical and dark matter-only simulations of galaxy clusters, revealing that dark matter-only models underestimate galaxy density in group centers, especially in dense regions, affecting predictions of structure and evolution.

Contribution

It provides a direct comparison of substructure in hydrodynamical and dark matter-only simulations, highlighting significant underestimations in galaxy densities by the latter.

Findings

Dark matter-only simulations underestimate galaxy density in cluster centers.

The underestimation is more pronounced in denser regions.

Dark matter-only simulations underpredict galaxy numbers in infalling groups by about four times.

Abstract

Dark matter-only simulations are able to produce the cosmic structure of a $\Lambda$CDM universe, at a much lower computational cost than more physically motivated hydrodynamical simulations. However, it is not clear how well smaller substructure is reproduced by dark matter-only simulations. To investigate this, we directly compare the substructure of galaxy clusters and of surrounding galaxy groups in hydrodynamical and dark matter-only simulations. We utilise TheThreeHundred project, a suite of 324 simulations of galaxy clusters that have been simulated with hydrodynamics, and in dark matter-only. We find that dark matter-only simulations underestimate the number density of galaxies in the centres of groups and clusters relative to hydrodynamical simulations, and that this effect is stronger in denser regions. We also look at the phase space of infalling galaxy groups, to show that dark matter-only simulations underpredict the number density of galaxies in the centres of these groups by about a factor of four. This implies that the structure and evolution of infalling groups may be different to that predicted by dark matter-only simulations. Finally, we discuss potential causes for this underestimation, considering both physical effects, and numerical differences in the analysis.