KAT-7 observations of a mass-selected sample of galaxy clusters

TL;DR

This study used KAT-7 observations to investigate the occurrence of radio halos in a mass-selected sample of galaxy clusters, finding that bright radio halos are rare in less massive clusters, thus expanding understanding of their distribution.

Contribution

First observational study targeting low mass galaxy clusters with KAT-7 to analyze radio halo occurrence and its correlation with cluster mass.

Findings

Detected 3 candidate radio halos in the sample.

Established upper limits for radio halo power in ~50% of clusters.

Confirmed that bright radio halos are rare in less massive clusters.

Abstract

The presence of megaparsec-scale radio halos in galaxy clusters has already been established by many observations over the last two decades. The emerging explanation for the formation of these giant sources of diffuse synchrotron radio emission is that they trace turbulent regions in the intracluster medium, where particles are trapped and accelerated during cluster mergers. Our current observational knowledge is, however, mainly limited to massive systems. Here we present observations of a sample of 14 mass-selected galaxy clusters, i.e. $M_{\rm 500} > 4\times10^{14}$~M${_\odot}$, in the Southern Hemisphere, aimed to study the occurrence of radio halos in low mass clusters and test the correlation between the radio halo power at 1.4 GHz $P_{\rm 1.4}$ and the cluster mass $M_{\rm 500}$. Our observations were performed with the 7-element Karoo Array Telescope at 1.86 GHz. We found three candidates to host diffuse cluster-scale emission and derived upper limits at the level of $0.6 - 1.9 \times 10^{24}$~Watt~Hz$^{-1}$ for $\sim 50\%$ of the clusters in the sample, significantly increasing the number of clusters with radio halo information in the considered mass range. Our results confirm that bright radio halos in less massive galaxy clusters are statistically rare.