Bright Type IIP Supernovae in Low-metallicity Galaxies

Abstract

We present measurements of the pseudo-equivalent width of the Fe ii λ 5018 absorption feature in the spectra of 12 Type IIP supernovae (SNe II) in low-luminosity ( M > −17) dwarf host galaxies. The Fe ii λ 5018 line has been called a useful diagnostic of the metallicity of the supernova (SN) progenitor stars. The events in our sample were discovered photometrically by the PanSTARRS Survey for Transients, and classified spectroscopically by us. Comparing our sample to 24 literature SNe II, we find that those in low-luminosity hosts have significantly weaker Fe ii features, with a probability of 10 −4 that the two samples are drawn from the same distribution. Because low-mass galaxies are expected to contain a lower fraction of metals, our findings are consistent with a metallicity dependence for Fe ii λ 5018, and therefore support the use of this line as a metallicity probe, in agreement with a number of recent works. In addition, we find that the SNe in faint (low-metallicity) hosts may be more luminous on average than those in the literature sample, suggesting possible physical differences between Type IIP SNe at low and high metallicity. However, accurate determinations of host galaxy extinction will be needed to quantify such an effect.