Observations of extended radio emission in clusters

TL;DR

This paper reviews observations of large-scale radio emissions in galaxy clusters, highlighting evidence for intracluster magnetic fields and relativistic electrons, and discusses implications for particle acceleration mechanisms and future research prospects.

Contribution

It provides a comprehensive review of observational evidence for non-thermal phenomena in galaxy clusters and discusses the implications for electron acceleration processes.

Findings

Evidence for large-scale intracluster magnetic fields.

Detection of relativistic electrons via radio emissions.

Insights into acceleration mechanisms like turbulence and shocks.

Abstract

We review observations of extended regions of radio emission in clusters; these include diffuse emission in `relics', and the large central regions commonly referred to as `halos'. The spectral observations, as well as Faraday rotation measurements of background and cluster radio sources, provide the main evidence for large-scale intracluster magnetic fields and significant densities of relativistic electrons. Implications from these observations on acceleration mechanisms of these electrons are reviewed, including turbulent and shock acceleration, and also the origin of some of the electrons in collisions of relativistic protons by ambient protons in the (thermal) gas. Improved knowledge of non-thermal phenomena in clusters requires more extensive and detailed radio measurements; we briefly review prospects for future observations.