Nearby Supernova Rates from the Lick Observatory Supernova Search (LOSS)

Weidong Li
UC Berkeley

In this talk I will present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have obtained 2.3 million observations of ~15,000 sample galaxies over an interval of 11 years (March 1998 through Dec. 2008). We considered 1036 SNe detected in our sample and used an optimal subsample of 726 SNe (274 SNe Ia, 116 SNe Ibc, 324 SNe II) to determine our SN rates. This is the largest and most homogeneous set of nearby SNe ever assembled for this purpose, and ours is the first local SN rate analysis based on CCD imaging and modern image-subtraction techniques. I will talk about the properties of our sample galaxies, the derivation of the luminosity function of SNe Ia from a complete sample to help with the rate calculations, and the correlations between SN rates and their host galaxy properties. We find that there is a significant rate-size relation: the galaxies of smaller sizes (luminosities or masses) have bigger SN rates (after normalized by its size). I will discuss the implication of this relation and whether it is connected to the star formation histories of the sample galaxies. I will also discuss the popular two-component ("prompt" and "delayed") model for the SN Ia rates and what we have learned from our search.