The rate and the origin of type Ia supernovae in radiogalaxies

Abstract

An analysis of type Ia supernova (SNIa) events in early type galaxies from Evans et al (1989) database provides strong evidence that the rate of type Ia supernovae (SNe) in radio-loud galaxies is about 6 times higher than the rate measured in radio-quiet galaxies, i.e. SNIa-rate$(radio-loud galaxies)=0.47^{+0.23}_{-0.15} h^2_{50}$ SNe per century and per 10$^{10}$L$^{B}_\odot$ (SNU) as compared to SNIa-rate$(radio-quiet galaxies)\lsim 0.080 h^2_{50}$ SNU. The exact value of the enhancement is still rather uncertain, but is likely to be in the range $\sim 4-15$. We discuss the possible causes of this result and we conclude that that the enhancement of SNIa explosion rate in radio-loud galaxies has the same common origin as their being strong radio sources, but that there is no causality link between the two phenomena. We argue that repeated episodes of interaction and/or mergers of early type galaxies with dwarf companions are responsible for inducing both strong radio activity in $\sim$14% of early type galaxies, and the $\sim1$ Gyr old stellar population needed to supply an adequate number SNIa progenitors. Within this scenario we predict that the probability of detecting a core-collapse SN event in radio-loud elliptical galaxies amounts to about 4% of their SNIa events.