Determination of the Hubble constant, the intrinsic scatter of luminosities of Type Ia SNe, and evidence for non-standard dust in other galaxies

A sample of 109 type Ia supernovae (SNe Ia) with recession velocity . 30,000 km s, is compiled from published SNe Ia light curves to explore the expansion rate of the local Universe. Based on the color parameter ∆C12 and the decline rate ∆m15, we found that the average absorption to reddening ratio for SN Ia host galaxies to be RUBV I = 4.37±0.25, 3.33±0.11, 2.30±0.11, 1.18±0.11, which are systematically lower than the standard values in the Milky Way. We investigated the correlations of the intrinsic luminosity with light curve decline rate, color index, and supernova environmental parameters. In particular, we found SNe Ia in E/S0 galaxies to be brighter close to the central region than those in the outer region, which may suggest a possible metallicity effect on SN luminosity. The dependence of SN luminosity on galactic environment disappears after corrections for the extinction and ∆C12. The Hubble diagrams constructed using 73 Hubble flow SNe Ia yield a 1-σ scatter of .0.12 mag in BV I bands and ∼0.16 mag in U band. The luminosity difference between normal SNe Ia and peculiar objects (including SN 1991bg-like and 1991T-like events) has now been reduced to within 0.15 mag via ∆C12 correction. We use the same precepts to correct the nearby SNe Ia with Cepheid distances and found that the fully corrected absolute magnitudes of SNe Ia are: MB = −19.33±0.06,MV = −19.27±0.05. We deduced a value for the Hubble constant of H0 = 72 ± 6 (total) km s −1 Mpc. Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing, 100084, P R China; wang [email protected] National Astronomical Observatories of China, Chinese Academy of Sciences, Beijing 100012, P R China; [email protected] LPNHE, CNRS-IN2P3, University of Paris VI&VII, Paris, France E.O. Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA94720, USA Department of Astronomy, Beijing Normal University, 100875, Beijing, China