Studying Transients Through the Metallicity Distributions of Their Host Galaxies

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.

John Graham
Thursday, January 21, 2021 - 12:30PM to Thursday, January 21, 2021 - 1:30PM