K.S. Dwarakanath (Raman Research Institute)
Galaxy clusters are some of the largest gravitationally bound structures in the Universe. Satellite observations during the early 70’s discovered diffuse X-ray emitting hot gas in the clusters. Cluster-wide non-thermal radio emission was also subsequently discovered in some of the X-ray bright clusters and has been a topic of multi-wavelength studies ever since. This radio emission, which is not associated with any of the cluster galaxies, arises due to relativistic particles and magnetic fields in the Intra Cluster Medium and is extended over millions of light years, similar to the extent of the hot and tenuous X-ray emitting gas found in galaxy clusters. Such large scale radio emission has posed challenges to its imaging and its understanding. The basic issues concern the production and sustenance of relativistic particles and magnetic fields over millions of light years. One of the currently popular model invokes cluster mergers to explain the existence of diffuse radio emission in clusters. But, there are alternative scenarios.
Over the last five decades much progress has been made on both the observational and theoretical fronts; resolving some of the earlier issues, but, raising many new questions. I will summarise the current status in this area of research and highlight some of the outstanding problems. Improvements in modeling and simulations and the emergence of next generation radio telescopes like the MWA, LOFAR and the SKA are expected to play a significant role in addressing some of these problems.