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5th of April 2023
ASKAP discovery of a 600 kpc complex radio source in Abell 3718
by Loi et al.
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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