Abstracts Astronomy & Space Science

The rate of supernovae in the nearby and distant universe

by David J Reiss

I present a measurement of the rate of supernovae (SNe) in nearby field and cluster galaxies, plus in distant field galaxies. The nearby rates are computed from the SNe discovered during the Mount Stromlo Abell Cluster SN Search (MSACSS), whose design, implementation, and results I discuss in detail. The distant rates are measured from the High-Z SN search, as a secondary result of the quest to measure the acceleration of the expansion of the universe using type-Ia SNe. The rates presented here provide a means of tracing the progenitor populations of the SNe through the ages of their host galaxies. In general, it is found that the rate of type-Ia SNe is largely independent of the age of the underlying stellar population, implying that the mean lifetime of SN-Ia progenitors is ≳ 1 Gyr, although there appears to be some evidence that their lifetimes must be shorter than a few Gyr. The rate of core-collapse SNe, as expected, seems to follow the same trend of star-formation in the field relative to clusters. Unfortunately the statistical and systematic uncertainties in these rates are large, and the significance of any of these trends is only at the ∼1-sigma level. However, the results do reveal the strength of using a comparison of SN rates of various types and among different galaxy populations to constrain quantities, from the nature of SN Ia progenitors to the star-formation and enrichment histories of the universe, to certain cosmological parameters. A measurement of supernova rates per unit volume independently confirms the previously-reported observation that the star-formation rate appears to have decreased markedly in the past few Gyr.