Gas sloshing, cold fronts, Kelvin-Helmholtz instabilities and the merger history of the cluster of galaxies Abell 496

TL;DR

This study combines observations and hydrodynamical simulations to understand gas sloshing, cold fronts, and instabilities in galaxy cluster Abell 496, revealing merger dynamics and their effects on cluster features.

Contribution

It provides a detailed simulation-based explanation of cold front formation and Kelvin-Helmholtz instabilities in Abell 496 caused by a minor merger.

Findings

Simulations reproduce observed spiral brightness residuals and cold front positions.

Kelvin-Helmholtz instabilities occur when the subcluster passes within 100 kpc of the core.

Sloshing causes mild oscillations but does not significantly alter global ICM profiles.

Abstract

We investigate the origin and nature of the multiple sloshing cold fronts in the core of Abell 496 by direct comparison between observations and dedicated hydrodynamical simulations. Our simulations model a minor merger with a 4{\times}10^13M{\circ} subcluster crossing A496 from the south-west to the north-north-east, passing the cluster core in the south-east at a pericentre distance 100 to a few 100 kpc about 0.6 to 0.8 Gyr ago. The gas sloshing triggered by the merger can reproduce almost all observed features, e.g. the characteristic spiral-like brightness residual distribution in the cluster centre and its asymmetry out to 500 kpc, also the positions of and contrasts across the cold fronts. If the subcluster passes close (100 kpc) to the cluster core, the resulting shear flows are strong enough to trigger Kelvin-Helmholtz instabilities that in projection resemble the peculiar kinks in the cold fronts of Abell 496. Finally, we show that sloshing does not lead to a significant modification of the global ICM profiles but a mild oscillation around the initial profiles.