An azimuthally resolved study of sloshing cold fronts in three nearby galaxy clusters

TL;DR

This study analyzes sloshing cold fronts in three galaxy clusters using Chandra X-ray data, revealing pressure deficits and suggesting magnetic fields and viscosity play roles in maintaining cold front sharpness.

Contribution

It provides the first azimuthally resolved analysis of sloshing cold fronts, highlighting the importance of magnetic fields and viscosity in their stability.

Findings

Pressure deficits inside cold fronts contrast with stripping cold fronts.

No significant azimuthal velocity gradients detected.

Magnetic fields and viscosity likely contribute to cold front stability.

Abstract

We present a detailed analysis of sloshing cold fronts in a sample of three nearby galaxy clusters (Abell 496, Abell 2029, and Abell 1644) observed with the Chandra X-ray Observatory. Cold fronts manifest as sharp edges in the X-ray surface brightness of the intracluster medium (ICM) in galaxy clusters. In the residual X-ray surface brightness maps, where the global ICM distribution has been subtracted, cold fronts generated by gas sloshing are observed at the boundaries of the spiral excesses. We perform a systematic and comprehensive study of the surface brightness edges along the spiral excesses. We find the deficit of the thermal pressure radially inward of the brightness edges, in contrast to stripping cold fronts that typically exhibit higher thermal pressure in brightness edges. Assuming that the sharp edges in the X-ray surface brightness distributions are sustained entirely by the gas bulk motions, we estimate the velocity gradients across the edges that are required to compensate for the deficit of the thermal pressure. We do not find statistically significant velocity gradients along the azimuthal direction. Our results suggest that alternative mechanisms such as magnetic fields and viscosity are necessary to maintain the sharpness of sloshing cold fronts.