Radio emission in a random magnetic field: Radio haloes and the structure of the magnetic field in the Coma cluster

Abstract

Μodels of cluster radio haloes have been constructed allowing for a random magnetic field. The resulting halo is far from smooth, both in intensity and polarization. The magnetic field must therefore be tangled on sufficiently small scales to reduce intensity fluctuations to observed levels. The smoothness of the inner regions of the radio halo in the Coma cluster, with fluctuations at about the 5 per cent level at 1-arcmin resolution, indicates that the outer scale of magnetic field fluctuations is less than 15 kpc