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

Peter C. Tribble

CITA, 60 St. George Street, Toronto M5S 1A1, Canada

Accepted 1991 June 27. Received 1991 June 25; in original form 1991 April 16.


Models of cluster radio halos 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% level at 1 arcmin resolution, indicates that the outer scale of magnetic field fluctuations is less than 15 kpc. Similar considerations indicate that less than 10% of the total halo emission can be due to galactic wakes and demonstrate that the halo emission and the magnetic field are spread throught the whole volume of the cluster and are not localized with a small filling factor. In the simplest models the fractional polarization should be similar to the fluctuation level, although the polarization can be substantially decreased if the field has a high degree of symmetry.


Radio emission in a random magnetic field
Comparison with the Coma radio halo
Galactic Wakes
Relation to Rotation measure and polarization data

This article appeared in Monthly Notices of the Royal Astronomical Society, vol 253, pp. 147-152 (1991). Copyright Royal Astronomical Society.
Unfortunately I don't have the original images that appeared in the paper still online here, so the figures aren't included. Given time, I may remedy this, but in the meantime there's just a bit of TeX garbage where the figures are supposed to go. Sorry about that.
Peter Tribble,