The intrinsic magnetic field orientation in NGC 4631

Abstract

We present radio continuum measurements of the edge-on spiral galaxy NGC 4631 at 4.86 and 8.44 GHz. We discuss the morphology of the radio halo in total and polarized emission and its wavelength dependence. The rotation measure and intrinsic magnetic field orientation are determined using the two frequency pairs 4.86/8.44 GHz and 1.49/4.86 GHz, the latter with the help of published 1.49 GHz data. The results can be summarized as follows: i) The rotation measure in the radio halo is between −15 and +20 rad m −2 . The intrinsic large-scale B-field in the halo is quite symmetric with respect to the major and minor axes of NGC 4631. It generally points to, or away from the central 5 kpc. ii) The prominent radio spurs of NGC 4631 are found to be an essential constituent of the radio halo