On the coherent rotation of diffuse matter in numerical simulations of galaxy clusters

TL;DR

This study investigates the coherent rotation of intracluster medium and dark matter in simulated galaxy clusters, revealing that a small fraction exhibit rotation and that dark matter dominates cluster dynamics.

Contribution

It provides the first detailed analysis of rotational motions in simulated galaxy clusters across different gas physics models, highlighting the limited rotation and dominance of dark matter.

Findings

Only 4% of relaxed clusters are rotating.

Dark matter's velocity dispersion dominates over tangential velocity.

Rotation profiles do not follow a solid body model.

Abstract

We present a study on the coherent rotation of the intracluster medium and dark matter components of simulated galaxy clusters extracted from a volume-limited sample of the MUSIC project. The set is re-simulated with three different recipes for the gas physics: $(i)$ non-radiative, $(ii)$ radiative without AGN feedback, and $(iii)$ radiative with AGN feedback. Our analysis is based on the 146 most massive clusters identified as relaxed, 57 per cent of the total sample. We classify these objects as rotating and non-rotating according to the gas spin parameter, a quantity that can be related to cluster observations. We find that 4 per cent of the relaxed sample is rotating according to our criterion. By looking at the radial profiles of their specific angular momentum vector, we find that the solid body model is not a suitable description of rotational motions. The radial profiles of the velocity of the dark matter show a prevalence of the random velocity dispersion. Instead, the intracluster medium profiles are characterized by a comparable contribution from the tangential velocity and the dispersion. In general, the dark matter component dominates the dynamics of the clusters, as suggested by the correlation between its angular momentum and the gas one, and by the lack of relevant differences among the three sets of simulations.