Metallicity from Type II supernovae from the (i)PTF ^⋆

¹ The Oskar Klein Centre, Department of AstronomyStockholm University, AlbaNova, 10691 Stockholm, Sweden
e-mail: ftadd@astro.su.se
² Department of Particle Physics & Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel
³ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁴ Las Cumbres Observatory Global Telescope, 6740 Cortona Dr, Suite 102, Goleta, CA 93117, USA
⁵ Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106, USA
⁶ Astronomy Department, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
⁸ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹⁰ Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
¹¹ Astronomy Department, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801, USA
¹² Department of Astronomy, University of Texas, Austin, TX 78712, USA
¹³ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, 100012 Beijing, PR China

Received: 16 December 2015
Accepted: 7 February 2016

Abstract

Type IIP supernovae (SNe IIP) have recently been proposed as metallicity (Z) probes. The spectral models of Dessart et al. (2014, MNRAS, 440, 1856) showed that the pseudo-equivalent width of Fe ii 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 < 0.4 Z_⊙. 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.