The structure of young supernova remnants in M82

Abstract

We have used the enhanced MERLIN at 5 GHz to image the central 700 pc of the nearby starburst galaxy M82. We detect in excess of 40 discrete sources, all of which are resolved by the MERLIN 50-mas (0.75-pc) beam. The observations confirm that most of the discrete sources are supernova remnants. Several show complete shells, and many more show structure consistent with partial shells. We have measured the sizes, flux densities and radio brightnesses of 23 of the sources, and show that they follow a surface brightness/diameter relation consistent with that found in the LMC and Galactic remnants. The cumulative number as a function of diameter appears to increase linearly to diameters of at least 3 pc, and indicates a supernova rate of 0.05 per year if the shells are expanding at 5000 km s −1