Type II Plateau supernovae as metallicity probes of the Universe

We explore a method for metallicity determinations based on quantitative spectroscopy of Type II-Plateau supernovae (SNe II-P). For consistency, we first evolve a set of 15 M_⊙ main-sequence stars at 0.1, 0.4, 1, and 2 times the solar metallicity. At the onset of core collapse, we trigger a piston-driven explosion and model the resulting ejecta and radiation. Our theoretical models of such red supergiant star explosions at different metallicity show that synthetic spectra of SNe II-P possess optical signatures during the recombination phase that are sensitive to metallicity variations. This sensitivity can be quantified and the metallicity inferred from the strengths of metal-line absorptions. Furthermore, these signatures are not limited to O, but also include Na, Ca, Sc, Ti, or Fe. When compared to a sample of SNe II-P from the Carnegie SN Project and previous SN followup programmes, we find that most events lie at a metallicity between 0.4 and 2 times solar, with a marked scarcity of SN II-P events at small magellanic cloud metallicity. This most likely reflects the paucity of low-metallicity star-forming regions in the local Universe.

SNe II-P have high-plateau luminosities that make them observable spectroscopically at large distances. Because they exhibit signatures of diverse metal species, in the future they may offer a means to constrain the evolution of the composition (e.g. the O/Fe ratio) in the Universe out to a redshift of 1 and beyond.