The Rate and the Origin of Type Ia Supernovae in Radio Galaxies

An analysis of Type Ia supernova (SN Ia) events in early-type galaxies from the Evans et al. database provides strong evidence that the rate of SNe Ia in radio-loud galaxies is about 6 times higher than the rate measured in radio-quiet galaxies, i.e., SN Ia rate (radio-loud galaxies) = 0.47 h SNe per century and per 10 10 L (SNU) as compared to SN Ia rate (radio-quiet galaxies) ≲ 0.080 h SNU. The exact value of the enhancement is still rather uncertain, but it is likely to be in the range ~4-15. We discuss the possible causes of this result, and we conclude that the enhancement of the SN Ia 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 ~14% of early-type galaxies and the ~1 Gyr old stellar population needed to supply an adequate number of SN Ia 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 SN Ia events.