On the connection between giant radio halos and cluster mergers

TL;DR

This study statistically confirms that giant radio halos are predominantly found in dynamically disturbed, merging galaxy clusters, supporting the theory that mergers energize the non-thermal emission responsible for radio halos.

Contribution

First comprehensive statistical analysis linking cluster dynamical state with the presence of radio halos using deep radio and X-ray data.

Findings

Radio halos are associated with disturbed, merging clusters.

Clusters without radio halos tend to be more relaxed.

Few exceptions where disturbed clusters lack halos.

Abstract

The frequently observed association between giant radio halos and merging galaxy clusters has driven present theoretical models of non-thermal emission from galaxy clusters, which are based on the idea that the energy dissipated during cluster-cluster mergers could power the formation of radio halos. To quantitatively test the merger-halo connection we present the first statistical study based on deep radio data and X-ray observations of a complete X-ray selected sample of galaxy clusters with X-ray luminosity > 5x 10^44 erg/s and redshift 0.2<z< 0.32. Using several methods to characterize cluster substructures, namely the power ratios, centroid shift and X-ray brightness concentration parameter, we show that clusters with and without radio halo can be quantitatively differentiated in terms of their dynamical properties. In particular, we confirm that radio halos are associated to dynamically disturbed clusters and cluster without radio halo are more "relaxed", with only a couple of exceptions where a disturbed cluster does not exhibit a halo.