Type IA supernovae in late type galaxies - Reddening correction, scale height, and absolute maximum magnitude

We have collected and analyzed the color excess data for the best photometrically studied type Ia supernovae (SNIa) which occurred in late type galaxies. From these data we find a ratio of the B band to selective extinction in the parent galaxies of RB_ = AB_/E (B-V) =3. 35+/-0. 25 (1σ). This indicates that the extinction curves in latetype galaxies have similar properties to that of our Galaxy. We obtain a new calibration for the absolute magnitude at maximum of SNIa in late type galaxies = - 19. 24+/-0. 18 (1σ) + 5 log (H₀_/75), which is marginally brighter than the recent determinations for type Ia supernovae observed in elliptical (dust-free) galaxies, and appears to confirm the potential of SNIa as standard candles for distance determinations. Studying the distribution of the extinction in the parent galaxies we find an average half-width of selective extinction of DELTAE (B-V) =0. 13+/-0. 04 and a dispersion of extinction to SNe of σE (B-V) =0. 15+/-0. 01. Allowing for extinction biases, the total width of the dust disk turns out to be 2τ₀_= 1. 28+/-0. 23 mag. These results imply that SNIa have a considerably broader distribution than the dust disk and confirm that they are older than old disk population objects, i. e. , age > 1-2 billion years. Also, we conclude that total extinction thickness of late type galaxies is very similar to that of the Milky Way.