Using the local gas-phase oxygen abundances to explore a metallicity dependence in SNe Ia luminosities

We present an analysis of the gas-phase oxygen abundances of a sample of 28 galaxies in the local Universe (z < 0.02) hosting Type Ia supernovae (SNe Ia). The data were obtained with the 4.2 m William Herschel Telescope. We derive local oxygen abundances for the regions where the SNe Ia exploded by calculating oxygen gradients through each galaxy (when possible) or assuming the oxygen abundance of the closest HII region. The sample selection only considered galaxies for which distances not based on the SN Ia method are available. Then, we use a principal component analysis to study the dependence of the absolute magnitudes on the colour of the SN Ia, the oxygen abundances of the region where they exploded and the stretch of the SN light curve. We demonstrate that our previous result suggesting a metallicity dependence on the SN Ia luminosity for non-reddened SNe Ia can be extended to our whole sample. These results reinforce the need of including a metallicity proxy, such as the oxygen abundance of the host galaxy, to minimize the systematic effect induced by the metallicity dependence of the SN Ia luminosity in future studies of SNe Ia at cosmological distances.