| Supernova remnants (SNRs) are thought to be the primary sites of cosmic ray acceleration in galaxies, and in this thesis we investigate how the properties of radio SNRs---and the physics of particle acceleration---depend on their parent galaxies. We combine new data with results compiled from the literature to investigate the radio continuum luminosity function of SNRs in 22 nearby galaxies, ranging from dwarf irregulars to luminous starbursts. We find that the luminosity functions can all be modeled with a power law of constant index, and an amplitude which depends on a combination of galaxy star formation rate and interstellar medium (ISM) density. These results can be fit with a simple cartoon model where the magnetic fields in SNRs are significantly amplified above ambient ISM values and the efficiency of cosmic ray acceleration is constant across galaxies. The luminosity of a galaxy's brightest SNR scales with star formation rate, and we find that the Milky Way falls on the measured correlation if we assume a star formation rate of 2 M⊙ yr--1 (synthesized from the literature) and that Cassiopeia A is the most luminous SNR in our Galaxy. As a first step in expanding studies of SNRs to non-star-forming galaxies, we also describe our discovery of an SNR candidate in a globular cluster around the gas-poor S0 galaxy NGC 7457. |
