Improving SN Ia Standardization with Host Galaxy Mass and Local Stellar Age

Over the last decade Type Ia Supernovae (SNe Ia) are standardized using both light-curve and host galaxy properties. We perform a simultaneous fit of both light-curve and host galaxy standardization coefficients. We find a correlation between the light-curve shape and stellar mass corrections, indicating that searches for correlations between Hubble-Lemaître residuals and host galaxy properties are biased. We find results consistent with a change in the color standardization term as a function of host stellar mass. Of all the tested models, the combination of host stellar mass and local age (seen at >3σ) increases the precision of SNe Ia distances by 10%. This is not seen when standardizing with global age. This combination is consistent with either metallicity or line-of-sight dust affecting the observed luminosity of SNe Ia.