The Dependence of the Type Ia Supernova Host Bias on Observation or Fitting Technique

Abstract

More luminous Type Ia supernovae (SNe Ia) prefer less massive hosts and regions of higher star formation. This correlation is inverted during width-color-luminosity light curve standardization resulting in step-like biases of distance measurements with respect to host properties. Using the PISCO supernova host sample and SDSS, GALEX, and 2MASS photometry, we compare host stellar mass and specific star formation rate (sSFR) from different observation methods, including local vs. global, and fitting techniques to measure their impact on the host step biases. Mass step measurements for all our mass samples are consistent within a 1$\sigma$ significance from -0.03$\pm$0.02 mag to -0.04$\pm$0.02 mag. Including or excluding UV information had no effect on measured mass step size or location. Specific SFR (sSFR) step sizes are more significant than mass step measurements and varied from $0.05\pm0.03$ mag (H$\alpha$) and $0.06\pm0.02$ mag (UV) for a 51 host sample. The sSFR step location is influenced by mass sample used to normalize star formation and by sSFR tracer choice. The step size is reduced to 0.04$\pm$0.03 mag when using all available 73 hosts with H$\alpha$ measurements. This 73 PISCO host subsample overall lacked a clear step signal, but here we are searching for whether different choices of mass or sSFR estimation can create a step signal. We find no evidence that different observation or fitting techniques choice can create a distance measurement step in either mass or sSFR.