Type II supernovae as probes of environment metallicity: observations of host HII regions

TL;DR

This study evaluates the potential of Type II supernovae as indicators of host galaxy metallicity by comparing spectral metal line strengths with environment oxygen abundances, confirming a significant correlation especially with Fe 5018 A line at 50 days post explosion.

Contribution

It provides observational evidence supporting the use of SNII spectral features as reliable metallicity diagnostics, with a comprehensive analysis of host HII-region abundances and supernova spectral data.

Findings

Significant correlation between Fe 5018 A equivalent width and host metallicity.

SNII explode at metallicities similar to or higher than the LMC.

No strong correlation between progenitor metallicity and SN light-curve or spectral diversity.

Abstract

Spectral modelling of SNII atmospheres indicates a clear dependence of metal line strengths on progenitor metallicity. This motivates further work to evaluate the accuracy with which these SNe can be used as metallicity indicators. To assess this accuracy we present a sample of SNII HII-region spectroscopy, from which environment abundances are derived. These environment abundances are compared to the observed strength of metal lines in SN spectra. Combining our sample with measurements from the literature, we present oxygen abundances of 119 host HII regions, by extracting emission line fluxes and using abundance diagnostics. Then, following Dessart et al., these abundances are compared to equivalent widths of Fe 5018 A at various time and colour epochs. Our distribution of inferred SNII host HII-region abundances has a range of ~0.6 dex. We confirm the dearth of SNeII exploding at metallicities lower than those found (on average) in the Large Magellanic Cloud. The equivalent width of Fe 5018 A at 50 days post explosion shows a statistically significant correlation with host HII-region oxygen abundance. The strength of this correlation increases if one excludes abundance measurements derived far from SN explosion sites. The correlation significance also increases if we only analyse a 'gold' IIP sample, and if a colour epoch is used in place of time. In addition, no evidence is found of correlation between progenitor metallicity and SN light-curve or spectral properties - except for that stated above with respect to Fe 5018 A equivalent width - suggesting progenitor metallicity is not a driving factor in producing the diversity observed in our sample. This study provides observational evidence of the usefulness of SNII as metallicity indicators. We finish with a discussion of the methodology needed to use SN spectra as independent metallicity diagnostics throughout the Universe.