On the multiplicity of supernovae within host galaxies

Abstract

Aims. We investigate the nature of multiple supernova hosting galaxies, and the types of events that they produce. Methods. Using all known historical supernovae, we split host galaxies into samples containing single or multiple events. These samples are then characterised in terms of their relative supernova fractions and host properties. Results. In multiple supernova hosts the ratio of type Ia to core-collapse events is lower than in single supernova hosts. For corecollapse events there is a suggestion that the ratio of types Ibc to type II events is higher in multiples than within single supernova hosts. This second increase is dominated by an increase in the number of SNIb. Within multiple supernova hosts, supernovae of any given type appear to “prefer” to explode in galaxies that are host to the same type of SN. We also find that multiple SN hosts have higher T-type morphologies. Conclusions. While our results suffer from low number statistics, we speculate that their simplest interpretation is that star formation within galaxies is generally of an episodic and bursty nature. This leads to the supernovae detected within any particular galaxy to be dominated by those with progenitors of a specific age, rather than a random selection from standard relative supernova rates, as the latter would be expected if star formation was of a long-term continuous nature. We further discuss the supernova progenitor and star formation properties that may be important for understanding these trends, and also comment on a range of important selection effects within our sample.