THE BLUE AND VISUAL ABSOLUTE MAGNITUDE DISTRIBUTIONS OF TYPE IA SUPERNOVAE

Tully-Fisher (TF), surface brightness fluctuation (SBF), and Hubble la w distances to the parent galaxies of Type Ia supernovae (SNs Ia) are used in order to study the SN Ia blue and visual peak absolute magnitu de (M(B) and M(V)) distributions. We propose two objective cuts, each of which produces a subsample with small intrinsic dispersion in M. On e cut, which can be applied to either band, distinguishes between a su bsample of bright events and a smaller subsample of dim events, some o f which were extinguished in the parent galaxy and some of which were intrinsically subluminous. The bright events are found to be distribut ed with an observed dispersion of 0.3 less than or similar to sigma(ob s)(M) less than or similar to 0.4 about a mean absolute magnitude (($) over bar M(B) or ($) over bar M(V)). Each of the dim SNs was spectros copically peculiar and/or had a red B-V color; this motivates the adop tion of an alternative cut that is based on B-V rather than on M. To w it, SNs Ia that are both known to have -0.25 < B-T < +0.25 and not kno wn to be spectroscopically peculiar show observational dispersions of only sigma(obs)(M(B)) = sigma(obs)(M(V)) = 0.3. Because characteristic observational errors produce sigma(obs)(M) > 0.2, the intrinsic dispe rsion among such SNs Ia is sigma(obs)(M) less than or equal to 0.2. Th e small observational dispersion indicates that SNs Ia, the TF relatio n, and SBFs all give good relative distances to those galaxies that pr oduce SNs Ia. The conflict between those who use SNs Ia in order to de termine the value of the Hubble constant (H-0) and those who use TF an d SBF distances to determine H-0 results from discrepant calibrations.