The role of baryons in self-interacting dark matter mergers

TL;DR

This study uses simulations to explore how baryonic matter influences dark matter-galaxy offsets during galaxy cluster mergers, revealing that the intracluster medium can amplify offsets at certain stages, offering insights into dark matter properties.

Contribution

It demonstrates that the intracluster medium affects dark matter-galaxy offsets at later merger stages, highlighting the importance of considering baryonic physics in dark matter studies.

Findings

ICM has minimal impact shortly after first pericentre

Offsets can be amplified at the first apocentre due to ICM

Observable offsets are possible with small enough dark matter cross-sections

Abstract

Mergers of galaxy clusters are promising probes of dark matter (DM) physics. For example, an offset between the DM component and the galaxy distribution can constrain DM self-interactions. We investigate the role of the intracluster medium (ICM) and its influence on DM-galaxy offsets in self-interacting dark matter models. To this end, we employ Smoothed Particle Hydrodynamics + N-body simulations to study idealized setups of equal- and unequal-mass mergers with head-on collisions. Our simulations show that the ICM hardly affects the offsets arising shortly after the first pericentre passage compared to DM-only simulations. But later on, e.g. at the first apocentre, the offsets can be amplified by the presence of the ICM. Furthermore, we find that cross-sections small enough not to be excluded by measurements of the core sizes of relaxed galaxy clusters have a chance to produce observable offsets. We found that different DM models affect the DM distribution and also the galaxy and ICM distribution, including its temperature. Potentially, the position of the shock fronts, combined with the brightest cluster galaxies, provides further clues to the properties of DM. Overall our results demonstrate that mergers of galaxy clusters at stages about the first apocentre passage could be more interesting in terms of DM physics than those shortly after the first pericentre passage. This may motivate further studies of mergers at later evolutionary stages.