Clusters of galaxies : observational properties of the diffuse radio emission

TL;DR

This paper reviews the observational properties of diffuse non-thermal radio emissions in galaxy clusters, discussing their classifications, magnetic fields, and implications for cluster formation, evolution, and large-scale structure, with insights from recent and future radio observations.

Contribution

It provides a comprehensive review of the properties, classifications, and origins of diffuse radio emissions in galaxy clusters, integrating recent observational data and models.

Findings

Diffuse radio emissions are common in galaxy clusters.

Large-scale magnetic fields are present in all clusters.

Non-thermal components are linked to cluster evolution and structure.

Abstract

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures...(abridged)... Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.