Is there an enormous cold front at the virial radius of the Perseus cluster?

TL;DR

This paper reports the discovery of the largest cold fronts ever observed in a galaxy cluster at the virial radius of Perseus, indicating large impact parameter mergers and magnetic field stabilization.

Contribution

First detection of enormous cold fronts at the virial radius of Perseus, combining XMM-Newton and Suzaku data to analyze their properties and implications for cluster dynamics.

Findings

Sharp surface brightness edges consistent with cold fronts

Temperature increases sharply outside the edges

Magnetic fields stabilize cold fronts at large radii

Abstract

We present new XMM-Newton observations extending the mosaic of the Perseus cluster out to the virial radius to the west. Previous studies with ROSAT have reported a large excess in surface brightness to the west, possibly the result of large scale gas sloshing, but lacked the spatial resolution and depth to determine if this excess lay behind a cold front. In our new XMM observations we have found that there is a sharp edge in X-ray surface brightness near the cluster virial radius (1.7Mpc) to the west, with a width comparable to the mean free path. The temperature measurements obtained with Suzaku data across this edge show that the temperature increases sharply outside this edge. All of these properties are consistent with this edge being the largest cold front ever observed in a galaxy cluster. We also find a second edge to the west, 1.2Mpc from the core, which also appears to be a cold front. Our results indicate that magnetic fields are able to stabilize the cold fronts against turbulence all the way out to the cluster virial radius. By comparing with numerical simulations, we find that these large cold fronts require large impact parameter, low mass ratio mergers which can produce fast gas motions without destroying the cluster core.