2016A&A...587L...7T

Type IIP supernovae (SNe IIP) have recently been proposed as metallicity (Z) probes. The spectral models of Dessart et al. (2014MNRAS.440.1856D) showed that the pseudo-equivalent width of FeII λ5018 (pEW₅₀₁₈) during the plateau phase depends on the primordial Z, but there was a paucity of SNe IIP exhibiting pEW₅₀₁₈ that were compatible with Z<0.4Z_☉. This lack might be due to some physical property of the SN II population or to the fact that those SNe have been discovered in luminous, metal-rich targeted galaxies. Here we use SN II observations from the untargeted (intermediate) Palomar Transient Factory [(i)PTF] survey, aiming to investigate the pEW₅₀₁₈ distribution of this SN population and, in particular, to look for the presence of SNe II at lower Z. We perform pEW₅₀₁₈ measurements on the spectra of a sample of 39 (i)PTF SNe II, selected to have well-constrained explosion epochs and light-curve properties. Based on the comparison with the pEW₅₀₁₈ spectral models, we subgrouped our SNe into four Z bins from Z≃0.1 Z_☉ up to Z≃2 Z_☉. We also independently investigated the Z of the hosts by using their absolute magnitudes and colors and, in a few cases, using strong-line diagnostics from spectra. We searched for possible correlations between SN observables, such as their peak magnitudes and the Z inferred from pEW₅₀₁₈. We found 11 events with pEW₅₀₁₈ that were small enough to indicate Z≃0.1 Z_☉. The trend of pEW₅₀₁₈ with Z matches the Z estimates obtained from the host-galaxy photometry, although the significance of the correlation is weak. We also found that SNe with brighter peak magnitudes have smaller pEW₅₀₁₈ and occur at lower Z.