The radio halos of spiral galaxies

Abstract

Models of the Galactic synchrontron radio-continuum emission are applied to the "edge-on' galaxies NGC 891 and NGC 4631, to see if they can account for the distribution of emission observed in then. It is concluded that the model which has an emissivity which decreases linearly from the plane to a height of ~6 kpc, can reasonably wall account for the distribution in M5-C 891, whereas for NGC 4631, the model which has a 'thick disc' of emission which varies with Galactocentric distance, can fairly well account for the high 25-emission observed there. Also in this thesis, the effect of spiral-arm irregularities on the synchrotron profile along the 'Galactic plane is investigated and the effect of spiral shocks on the irregular component of the magnetic field. It is shown that such irregularities can shift the peaks of maximum emission, in directions tangential to spiral-arms, through several degrees and also give rise to multiple peaks. The effect of the shock on the magnetic field is shown to decrease these peaks of emission.