Determination of the Hubble Constant, the Intrinsic Scatter of Luminosities of Type Ia Supernovae, and Evidence for Nonstandard Dust in Other Galaxies

Abstract

A sample of 109 type Ia supernovae (SNe Ia) with recession velocity < 30,000\nkm s^{-1}, is compiled from published SNe Ia light curves to explore the\nexpansion rate of the local Universe. Based on the color parameter delta C_{12}\nand the decline rate delta m_{15}, we found that the average absorption to\nreddening ratio for SN Ia host galaxies to be R_{UBVI} = 4.37+/-0.25,\n3.33+/-0.11, 2.30+/-0.11, 1.18+/-0.11, which are systematically lower than the\nstandard values in the Milky Way. We investigated the correlations of the\nintrinsic luminosity with light curve decline rate, color index, and supernova\nenvironmental parameters. In particular, we found SNe Ia in E/S0 galaxies to be\nbrighter close to the central region than those in the outer region, which may\nsuggest a possible metallicity effect on SN luminosity. The dependence of SN\nluminosity on galactic environment disappears after corrections for the\nextinction and delta C_{12}. The Hubble diagrams constructed using 73 Hubble\nflow SNe Ia yield a 1-sigma scatter of <0.12 mag in BVI bands and ~0.16 mag in\nU band. The luminosity difference between normal SNe Ia and peculiar objects\n(including SN 1991bg-like and 1991T-like events) has now been reduced to within\n0.15 mag via delta C_{12} correction. We use the same precepts to correct the\nnearby SNe Ia with Cepheid distances and found that the fully corrected\nabsolute magnitudes of SNe Ia are: M_{B} = -19.33+/-0.06 mag, M_{V} =\n-19.27+/-0.05 mag. We deduced a value for the Hubble constant of H_{0} = 72 +/-\n6 (total) km s^{-1} Mpc^{-1}.\n