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Description
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 {lambda}5018 (pEW_5018_) during the plateau phase depends on the primordial Z, but there was a paucity of SNe IIP exhibiting pEW_5018_ that were compatible with Z<0.4Z_{sun}_. 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 pEW_5018_ distribution of this SN population and, in particular, to look for the presence of SNe II at lower Z. We perform pEW_5018_ 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 pEW_5018_ spectral models, we subgrouped our SNe into four Z bins from Z=~0.1 Z_{sun}_ up to Z=~2 Z_{sun}_. 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 pEW_5018_. We found 11 events with pEW_5018_ that were small enough to indicate Z=~0.1 Z_{sun}_. The trend of pEW_5018_ 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 pEW_5018_ and occur at lower Z.
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