Supernovae in the nuclear regions of starburst galaxies

Abstract

The feasibility of using near-infrared observations to discover supernovae in the nuclear and circumnuclear regions of nearby starburst galaxies is investigated. We provide updated estimates of the intrinsic core-collapse supernova rates in these regions. We discuss the problem of extinction, and present new estimates of the extinction towards 33 supernova remnants in the starburst galaxy M 82. This is done using H i and H2 column density measurements. We estimate the molecular to atomic hydrogen mass ratio to be 7.4±1.0 in M 82. We have assembled near-infrared photometric data for a total of 13 core-collapse supernovae, some unpublished hitherto. This constitutes the largest database of infrared light curves for such events. We show that the infrared light curves fall into two classes, ‘ordinary’ and ‘slowly declining’. Template JHKL light curves are derived for both classes. For ordinary core-collapse supernovae, the average peak JHKL absolute magnitudes are −18.4, −18.6, −18.6 and −19.0 respectively. The slowly declining core-collapse supernovae are found to be significantly more luminous than the ordinary events, even at early times, having average peak JHKL absolute magnitudes of −19.9, −20.0, −20.0 and −20.4 respectively. We investigate the efficiency of a computerized image subtraction method in supernova detection. We then carry out a Monte Carlo simulation of a supernova search using K-band images of NGC 5962. The effects of extinction and observing strategy are discussed. We conclude that a modest observational programme will be able to discover a number of nuclear supernovae.