The influence of the environment on the rate of type Ia supernovae in radio galaxies

An analysis of Type Ia Supernova (SNIa) events in early type galaxies from the Cappellaro, Evans & Turatto (1999) database provides conclusive evidence that the rate of type Ia Supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate measured in radio-quiet galaxies, i.e. SNIa-rate(radio - loud galaxies) = 0.43(-0.14)(+0.19)h(75)(2) SNu as compared to SNIa-rate(radio quiet galaxies) = 0.11(-0.03)(+0.06)h(75)(2) SNu. The actual value of the enhancement is likely to be in the range similar to 2 - 7 (P similar to 10(-4)). We analyse the possible causes of this result and conclude that the enhancement of SNIa explosion rate in radio-loud galaxies has the same origin as their being strong radio sources, but 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, on times-scale of about 1 Gyr, are responsible for inducing both strong radio activity observed in similar to 14% of early type galaxies and to supply an adequate number of SNIa progenitors to the stellar population of ellipticals.