Uniqueness of galaxy groups in the structural hierarchy from its radio signature

Abstract

Galaxy groups are the intermediate structures in hierarchy of cosmic objects. Usually, galaxy clusters emerge out of mergers of groups of galaxies, but, no study confirms that groups are just the scaled down version of the clusters. In this work we have studied the thermal and non-thermal characteristics of galaxy groups from observational (SDSS catalogue) and theoretical (ENZO hydrodynamic simulations) point of view and compared them with the cluster properties. Our study shows that the mass scaling of both thermal and non-thermal properties of galaxy groups are deviating from cluster scale below 5 × 10 13 M. A prominent break in the scaling laws at 5 × 10 13 M has been observed in computed radio emission as well. We have also estimated the cosmic magnetic field using turbulent dynamo model for these objects and found to be at a level of sub-micro Gauss. Possible radio synchrotron emission from groups have been calculated using both Diffusive Shock Acceleration and Turbulent Re-acceleration models. It is observed that the total emission from some of the groups are much higher than what is expected from existing scaling laws. Such groups must be away from virialization and are at a highly dynamic state. Finally, we have predicted the expected radio flux from these highly active groups for possible detection by future telescopes (e.g. SKA, Upgraded GMRT etc.).