On the origin of the magnetic fields associated with radio haloes in galaxy clusters

Abstract

A model for the magnetic fields associated with cluster radio haloes is developed on the hypothesis that radio haloes arise from recent mergers of galaxy clusters. The magnetic fields and the associated relativistic electrons originate from a population of disrupted cluster radio galaxies in a merger event. An estimate of the size of the magnetic fields produced in merger events from the cluster radio sources was found to be about one order of magnitude smaller than the observed value for the Coma cluster. However, amplification of the magnetic field as well as acceleration of relativistic particles is expected to take place since large amounts of kinetic energy are available in such a collision. The radio luminosity produced by the synchrotron emission of both primary and secondary (derived from p-p collisions of primary relativistic protons with ambient thermal protons in the intracluster medium) electrons is estimated. It was found that the secondary electrons are not important compared with the primary electrons, for which only small boosting is sufficient to explain the observed radio luminosity of the Coma cluster.