Abstract:
Many transient phenomena are the deaths of massive short-lived stars. All else being equal, the physical properties of the galaxies in which these events occur should match those of the typical galaxy population weighted by star-formation rate. Of particular interest is metallicity, the ratio of elements heaver than helium to that of hydrogen. In prior work I showed that while the metallicity distribution of core-collapse supernovae (SNe) hosts do follow that of typical galaxies, Long-duration Gamma Ray Bursts (LGRBs) are predominately found in low metallicity host galaxies. Here I expand this analysis by looking at these populations individually, specifically how the LGRB metallicity distribution changes with redshift and the SNe metallicity distribution changes by SNe subtype. Surprisingly the LGRBs retain a consistent metallicity distribution throughout the 0< z < 2.5 range of our sample. This is in sharp contrast to typical galaxy populations, which were 0.2 to 0.3 dex poorer in metallicity at redshift 2.5 than today. Furthermore the LGRB host galaxy mass distribution increases with redshift so as to retain this constant metallicity distribution while also being consistent with known evolution in the mass-metallicity relation. To study metallicity distribution differences between SNe subtypes as large a sample as possible is needed. To this end I began by retrieving from the Transient Name Server ALL known SNe with IAUC names, then matched those with SDSS photometric objects. When this matched host galaxy had spectroscopy in the MPA-JHU galaxy emission line analysis, I computed the host galaxy’s metallicity, producing a SNe host metallicity catalog of just over 2400 objects. Comparing across SNe types reveals, for the first time, that Type IIn and IIb SNe have a significant preference for higher metallicity environments than the standard Type II SNe population. This sample is also the first to find that Type Ia-peculiar and Ia-91T-like SNe have a significant preference for lower metallicity environments than standard Ia SNe.
