Monday, July 25, 2011 - 11:30am
"Turbulence and magnetic fields behind merger shocks in galaxy clusters, and applications to radio relics"
Abstract. The propagation of a merger shock through the intra-cluster medium (ICM) stirs the gas and amplifies the magnetic field. According to the commonly accepted model, the shock propagation is associated with the acceleration of cosmic ray electrons and with diffuse radio emission (radio relic). We study analytically a simple model of a merger shock moving through the ICM. It is shown that the stirring induced by the shock transit is not guaranteed to leave the post-shock region in a state of fully developed turbulence, because of the rather short timescale for the shock propagation (of the order of 1e8 yr). This can explain the high degree of polarisation of the radio emission. Furthermore, it appears that amplification of the magnetic field to values of the order of some microG is problematic to be obtained, unless additional processes beyond the turbulent dynamo are invoked.