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 la 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 R(B) = A(B)/E(B - V) = 3.35 +/- 0.25 (1-sigma). This indicates that the extinction curves in late type 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 [M(B)] = - 19.24 +/- 0.18(1-sigma) + 5 log(H0/75), which is marginally brighter than the recent determinations for type la 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 DELTA[E(B - V)] = 0.13 +/- 0.04 and a dispersion of extinction to SNe of sigma[E(B - V)] = 0.15 +/- 0.01. Allowing for extinction biases, the total width of the dust disk turns out to be 2-tau-0 = 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.