Type Ia Host Bias is Robust Across Different Observation Methods and Fitting Techniques

Brighter Type Ia supernovae (SNe Ia) prefer less massive host galaxies and regions of higher star formation, but the dependence on host property measurement technique on this bias is not known. Using the PISCO IFS sample of SN host galaxies alongside SDSS, GALEX, and 2MASS photometry, we compare host galaxy stellar mass and star formation rate (SFR) estimates using different observation methods and fitting techniques. Mass estimates were consistent regardless of fitting technique. For optical wavelengths, the magnitude correction size (“magnitude step”) for mass estimates varied from -0.04 mag for FAST++ and STARLIGHT to -0.02 mag for ZPEG. Including UV information for mass estimates results in a mass-dependent shift in mass but had no effect on measured mass step size or location. Regardless of technique, the measured magnitude step for global specific SFR (sSFR) was ∼0.1 mag; UV-calibrated SFR estimates were consistent with those from Hα. Only 49 hosts were used to measure the sSFR step as opposed to 76 FAST++ mass estimates or 97 STARLIGHT mass estimates to measure the mass step. Local sSFR step model fits were inconclusive due to a diminished sample size of 38 SNe Ia. Stronger correlation between GALEX UV photometry global and local sSFR estimates relative Hα estimates due to a large GALEX PSF inhibits its use to measure local UV 1 kpc flux. Overall, observation method and fitting technique had little influence on host bias detection. Instead, of importance is the property used to measure the host bias.