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