Classifications of the Host Galaxies of Supernovae, Set III

A homogeneous sample comprising host galaxies of 604 recent supernovae,including 212 objects discovered primarily in 2003 and 2004, has beenclassified on the David Dunlap Observatory system. Most SN 1991bg-like SNe Iaoccur in E and E/Sa galaxies, whereas the majority of SN 1991T-like SNe Iaoccur in intermediate-type galaxies. This difference is significant at the99.9% level. As expected, all types of SNe II are rare in early-type galaxies,whereas normal SNe Ia occur in all Hubble types. This difference is significantat the 99.99% level. A small number of SNe II in E galaxies might be due togalaxy classification errors, or to a small young-population component in thesemainly old objects. No significant difference is found between thedistributions over Hubble type of SNe Ibc and SNe II. This confirms that bothof these types of objects have similar (massive) progenitors. The present datashow that, in order to understand the dependence of supernova type onhost-galaxy population, it is more important to obtain accurate morphologicalclassifications than it is to increase the size of the data sample.Comment: Accepted for publishing in PAS