Dynamics and Magnetization in Galaxy Cluster Cores Traced by X-ray Cold Fronts

TL;DR

This paper investigates the dynamics and magnetic properties of cold fronts in galaxy cluster cores, revealing that shear flows beneath these fronts likely generate magnetic fields that stabilize the fronts and relate to observed radio minihalos.

Contribution

It provides a detailed analysis of the thermodynamic and flow properties beneath cold fronts, proposing a shear flow mechanism for magnetic field generation in galaxy cluster cores.

Findings

Pressure is continuous across cold fronts.

Significant centripetal acceleration is required beneath the fronts.

Shear flows likely generate magnetic fields that stabilize the fronts.

Abstract

Cold fronts (CFs) - density and temperature plasma discontinuities - are ubiquitous in cool cores of galaxy clusters, where they appear as X-ray brightness edges in the intracluster medium, nearly concentric with the cluster center. We analyze the thermodynamic profiles deprojected across core CFs found in the literature. While the pressure appears continuous across these CFs, we find that all of them require significant centripetal acceleration beneath the front. This is naturally explained by a tangential, nearly sonic bulk flow just below the CF, and a tangential shear flow involving a fair fraction of the plasma beneath the front. Such shear should generate near-equipartition magnetic fields on scales ~<50 pc from the front, and could magnetize the entire core. Such fields would explain the apparent stability of cool-core CFs and the recently reported CF-radio minihalo association.