The mechanisms driving the explosions of massive stars are not yet fully understood. Identifying the main parameters responsible for generating the variety of observed supernovae (SNe) is an essential goal. Mass is obviously an important factor, but the roles of binarity and metallicity are not fully known. One way to gain insight on the significance of these factors, is to compare the types of SNe occurring in bright metal-rich galaxies to those hosted by small dwarf galaxies (composed mostly of primordial Hydrogen and Helium with little heavy elements).
We perform this test with the first compilation of 72 core collapse SNe from the Palomar Transient Factory (PTF) and find a lack of stripped (type Ic) SNe in dwarf galaxies, offset by an excess of less stripped (type IIb) events there. We hypothesize that metallicity is an important factor determining the mass loss of massive stars, allowing them to explode as SNe IIb in dwarf metal-poor galaxies, but driving them towards stripped Ic events in giant galaxies. At the same time, we detect an excess of highly stripped broad lined Ic events in dwarf galaxies, suggesting that the stripping mechanism for the progenitors of these SNe is not metallicity-driven.
As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed further via the dwarf-galaxy SN population.