Metallicity from Type II Supernovae from the (i)PTF
  Type IIP supernovae (SNe IIP) have recently been proposed as metallicity
($Z$) probes. The spectral models of Dessart et al. (2014) showed that the
pseudo-equivalent width of Fe II $\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 $Z < 0.4$ ${\rm Z}_{\odot}$.
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 $Z
\approx 0.1$ $Z_{\odot}$ up to $Z \approx 2$ $Z_{\odot}$. 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 $Z \approx 0.1$ $Z_{\odot}$. 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 $Z$.
