The connection between radio halos and cluster mergers and the statistical properties of the radio halo population

TL;DR

This paper examines the statistical relationship between galaxy cluster mergers and the presence of radio halos, highlighting how merging clusters tend to host radio halos due to turbulence re-acceleration, with implications for future LOFAR surveys.

Contribution

It provides a statistical analysis linking radio halos to cluster dynamical states and discusses the role of turbulence in their formation, emphasizing the importance of upcoming surveys.

Findings

Radio bi-modality correlates with cluster dynamical state.

Merging clusters host radio halos and follow the radio--X-ray correlation.

Relaxed clusters lack radio halos and are separated from the correlation.

Abstract

We discuss the statistical properties of the radio halo population in galaxy clusters. Radio bi-modality is observed in galaxy clusters: a fraction of clusters host giant radio halos while the majority of clusters do not show evidence of diffuse cluster-scale radio emission. The radio bi-modality has a correspondence in terms of dynamical state of the hosting clusters showing that merging clusters host radio halos and follow the well known radio--X-ray correlation, while more relaxed clusters do not host radio halos and populate a region well separated from that correlation. These evidences can be understood in the framework of a scenario where merger-driven turbulence re-accelerate the radio emitting electrons. We discuss the main statistical expectations of this scenario underlining the important role of upcoming LOFAR surveys to test present models.