Fossil Radio Plasma in Cluster Merger Shock Waves

Abstract

In several merging clusters of galaxies so-called cluster radio relics have been observed. These are extended radio sources which do not seem to be associated with any radio galaxy. Two competing physical mechanisms to accelerate the radio emitting electrons have been proposed: (i) diffusive shock acceleration and (ii) adiabatic compression of fossil radio plasma by merger shock waves. Here the second scenario is investigated. We present detailed 3-dimensional magneto-hydrodynamical simulations of the passage of a radio plasma cocoon through a shock wave. Taking into account synchrotron, inverse Compton and adiabatic energy losses and gains we evolved the relativistic electron population to produce synthetic radio maps in Stokes I-, Q-, and U-polarisation. In the synthetic radio maps the electric polarisation vectors are mostly perpendicular to the filamentary radio structures.