Constraining the ages of supernova progenitors. I. Supernovae and spiral arms

We present the first results of a three-part study of supernova (SN) ages using positional age indicators in spiral galaxies. We have measured the positions of 90 spectroscopically identified Type Ia and Type II SNs (SNs Ia and SNs II) relative to spiral arms in their host galaxies, making a special effort to reduce inhomogeneity in the process of arm tracing for different galaxies. We find that SNs II are more tightly concentrated to the arms than SNs Ia, but both kinds of SNs occur closer to arms than a random disk population. However, when compared with the distribution of V and I light relative to the arms, the SNs Ia are no more tightly concentrated than the general stellar population. This indicates that SNs Ia occur in a population old enough to have diffused away from their formation regions.