Evidence for a pressure discontinuity at the position of the Coma relic from Planck Sunyaev-Zel'dovich effect data

TL;DR

This study provides tentative evidence of a pressure discontinuity at the Coma relic using Planck SZ data, supporting the shock origin of radio relics in galaxy clusters.

Contribution

First detection of a pressure jump at a radio relic using SZ effect data, linking it directly to the shock front in the Coma cluster.

Findings

Pressure discontinuity consistent with relic position

Mach number estimated at 2.9 (+0.8/-0.6)

Disfavours high-pressure filament and sub-cluster models

Abstract

Radio relics are Mpc-scale diffuse synchrotron sources found in galaxy cluster outskirts. They are believed to be associated with large-scale shocks propagating through the intra-cluster medium, although the connection between radio relics and the cluster merger shocks is not yet proven conclusively. We present a first tentative detection of a pressure jump in the well-known relic of the Coma cluster through Sunyaev-Zel'dovich (SZ) effect imaging.The SZE data are extracted from the first public all-sky data release of Planck and we use high-frequency radio data at 2.3 GHz to constrain the shock-front geometry. The SZE data provide evidence for a pressure discontinuity, consistent with the relic position, without requiring any additional prior on the shock-front location. The derived Mach number M = 2.9 (+0.8/-0.6) is consistent with X-ray and radio results. A high-pressure "filament" without any pressure discontinuity is disfavoured by X-ray measurements and a "sub-cluster" model based on the infalling group NGC 4839 can be ruled out considering the published mass estimates for this group. These results signify a first attempt towards directly measuring the pressure discontinuity for a radio relic and the first SZ-detected shock feature observed near the virial radius of a galaxy cluster.