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Galaxy clusters host an incredible realm of radio source diversity:
star forming galaxies, radio galaxies, remnant radio galaxies, radio
phoenixes, radio halos, radio relics, and mini-halos. The detection
and the classification of cluster-embedded radio sources provides
crucial information about the evolution of both clusters and cluster
galaxies and how the sources interact with the environment.
Loi et al. have conducted a multifrequency study of the
little-studied southern galaxy cluster Abell 3718. The cluster has a
mass ~3×10^14 solar masses and a radius of just under a million
parsecs (3.26 million light years). ASKAP observations at 943 MHz
revealed -- in addition to the compact radio sources at the
centre of the cluster (S2, S3 and S4) -- extended radio emission that is composed of three main
structures: (i) a compact radio galaxy associated with S1, (ii) a
southern radio galaxy associated with S5, and (iii) a faint radio arc
with a length of ∼612 kpc connecting the two structures in projection.
The ASKAP data was supplemented by ATCA, optical, and X-ray data to
examine merger activity in the cluster. The cluster appears to be in
a relaxed dynamical state, but there is clear asymmetry of the X-ray
surface brightness distribution perpendicular to the direction of the
largest angular extension of the radio source. The image above is a
multiwavelength image of Abell 3718. The background colour map shows
a composite optical image from the Dark Energy Survey. Red colours and
black contours trace the X-ray surface brightness measured in the
0.3--7 keV range by XMM-Newton, and white contours show the 943 MHz
ASKAP total intensity surface brightness. The team conclude the radio
arc, due to its morphology, could be either a radio relic or a tail
associated with a radio galaxy.
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