Cold Fronts by Merging of Shocks

TL;DR

This paper proposes that some galaxy cluster cold fronts are caused by shock mergers, resulting in characteristic density and temperature discontinuities that can extend to the virial shock, supported by 1D simulations.

Contribution

It introduces a novel mechanism for cold front formation through shock mergers, expanding understanding of cluster dynamics and cold front origins.

Findings

Shock mergers produce spherical cold fronts with specific density and temperature jumps.

Simulations show shock-induced cold fronts form during cluster perturbations like mergers.

Concentric cold fronts trace the expansion of the virial shock in clusters.

Abstract

Cold fronts (CFs) are found in most galaxy clusters, as well as in some galaxies and groups of galaxies. We propose that some CFs are relics of merging between two shocks propagating in the same direction. Such shock mergers typically result in a quasi-spherical, factor ~1.4-2.7 discontinuity in density and in temperature. These CFs may be found as far out as the virial shock, unlike what is expected in other CF formation models. As a demonstration of this effect, we use one dimensional simulations of clusters and show that shock induced cold fronts form when perturbations such as explosions or mergers occur near the cluster's centre. Perturbations at a cluster's core induce periodic merging between the virial shock and outgoing secondary shocks. These collisions yield a distinctive, concentric, geometric sequence of CFs which trace the expansion of the virial shock.