Radio halos in nearby (z < 0.4) clusters of galaxies

TL;DR

This paper compiles and analyzes data on 31 known nearby galaxy cluster radio halos, exploring their properties, correlations, and origins, and highlights the need for advanced telescopes to further understand these phenomena.

Contribution

The study provides a comprehensive dataset of radio halos in nearby clusters and confirms correlations, while also discovering new features and emphasizing the importance of next-generation radio telescopes.

Findings

Confirmed correlation between radio spectral index and cluster temperature.

Discovered diffuse radio emission in a low X-ray luminosity cluster.

Noted high occurrence of both relics and halos in clusters.

Abstract

The Intra-Cluster Medium is characterized by thermal emission, and by the presence of large scale magnetic fields. In some clusters of galaxies a diffuse non-thermal emission is also present, located at the cluster center and named radio halo. These sources indicate the existence of relativistic particles and magnetic fields in the cluster volume. In this paper we collect data on all known nearby cluster radio halos (z < 0.4), to discuss their statistical properties and to investigate their origin. We searched for published data on radio halos and reduced new and archive VLA data to increase the number of known radio halos. We present data on 31 radio halos, 1 new relic source, and 1 giant filament. We note the discovery of a small size diffuse radio emission in a cluster (A1213) with very low X-ray luminosity. Among statistical results we confirm the correlation between the average halo radio spectral index and the cluster temperature. We also discuss the high percentage of clusters where both a relic and a radio halo is present. The sample of radio halos discussed here represents the population of radio halos observable with present radio telescopes. The new telescope generation is necessary for a more detailed multifrequency study, and to investigate the possible existence of a population of radio halos with different properties.