2015MNRAS.446.3768H

Type Ia supernovae (SNeIa) display a complex relation with their host galaxies. An important prior to the fit of the supernovae's light curve is the distribution of host galaxy extinction values that can be encountered. The Sloan Digital Sky Survey SuperNova survey project has published light-curve fits using both mlcs2k2 and salt2. We use the former fits extinction parameter (AV) to map this distribution of extinction values. We explore the dependence of this distribution on four observables; the inclination of the host galaxy disc, radial position of the supernova, redshift of the supernova and host, and the level of star formation in the host galaxy. The distribution of AV values encountered by supernovae is typically characterized by :N_0 e^-A_V/τ, with τ = 0.4 or 0.33. We find that the inclination correction using an infinitely thin disc for the SN Ia is sufficient, resulting in similar exponential AV distributions for high- and low-inclination discs. The AV distribution also depends on the radial position in the disc, consistent with previous results on the transparency of spiral discs. The distribution of AV values narrows with increased star formation, possibly due to the destruction or dispersion of the dusty interstellar medium by stellar winds prior to the ignition of the supernova. In future supernova searches, certainly the inclination of the host galaxy disc, should be considered in the construction of the AV prior with τ = 0.4/cos(i) as the most likely prior in each individual host galaxy's case.