The supernova rate per unit mass

We compute the rate of supernovae ( SNe) of different types along the Hubble sequence normalized to the near-infrared luminosity and to the stellar mass of the parent galaxies. This is made possible by the new complete catalog of near-infrared galaxy magnitudes obtained by 2MASS. We find that the rates of all SN types, including Ia, Ib/ c and II, show a sharp dependence on both the morphology and the ( B - K) colors of the parent galaxies and, therefore, on the star formation activity. In particular we find, with a high statistical significance, that the type Ia rate in late type galaxies is a factor similar to 20 higher than in E/ S0. Similarly, the type Ia rate in the galaxies bluer than B - K = 2.6 is about a factor of 30 larger than in galaxies with B - K > 4.1. These findings can be explained by assuming that a significant fraction of Ia events in late spirals/ irregulars originates in a relatively young stellar component.