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

Xiaofeng Wang,Lifan Wang,R. Pain,Xu Zhou,Zong-wei Li

Published 2006 in The Astrophysical Journal

ABSTRACT

A sample of 109 Type Ia supernovae (SNe Ia) with recession velocity ≲30,000 km s-1 is compiled from published SN Ia light curves to explore the expansion rate of the local universe. Based on the color parameter ΔC12 and the decline rate Δm15, we found that the average absorption-to-reddening ratios for SN Ia host galaxies are RUBVI = 4.37 ± 0.25, 3.33 ± 0.11, 2.30 ± 0.11, and 1.18 ± 0.11, which are systematically lower than the standard values in the Galaxy. We investigated the correlations of the intrinsic luminosity with light-curve decline rate, color index, and SN environmental parameters. In particular, we found that SNe Ia in E/S0 galaxies close to the central region are brighter 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 ΔC12. The Hubble diagrams constructed using 73 Hubble flow SNe Ia yield a 1 σ scatter of ≲0.12 mag in BVI bands and ~0.16 mag in U band. The luminosity difference between normal SNe Ia and peculiar objects (including SN 1991bg-like and SN 1991T-like events) has now been reduced to within 0.15 mag via ΔC12 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 and MV = -19.27 ± 0.05. We deduced a value for the Hubble constant of H0 = 72 ± 6 (total) km s-1 Mpc-1.

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