Implications for the Hubble Constant from the First Seven Supernovae at [CLC][ITAL]z[/ITAL][/CLC] ≥ 0.35

Abstract

The Supernova Cosmology Project has discovered over 28 supernovae (SNs) at 0.35 < z < 0.65 in an ongoing program that uses Type la SNs (SN la's) as high-redshift distance indicators. Here we present measurements of the ratio between the locally observed and global Hubble constants, H o L H G , based on the first seven SNs of this high-redshift data set compared with 18 SNs atz ≤ 0.1 from the Calán/Tololo survey. If Ω ≤ 1, then light-curve width corrected SN magnitudes yield H o L H G < 1.10 (95% confidence level) in both a A = 0 and a flat universe. The analysis using the SN la's as standard candles without a light-curve width correction yields similar results. These results rule out the hypothesis that the discrepant ages of the Universe derived from globular clusters and recent measurements of the Hubble constant are attributable to a locally underdense bubble. Using the Cepheid-distance-calibrated absolute magnitudes for SN la's of Sandage et al., we can also measure the global Hubble constant, H o G . If ω M , ≥ 0.2, we find that H o G < 70 km s -1 Mpc -1 in a A = 0 universe and H o G < 78 km s -1 Mpc -1 in a flat universe, correcting the distant and local SN apparent magnitudes for light-curve width. Lower results for H o G are obtained if the magnitudes are not width-corrected. © 1997. The American Astronomical Society. All rights reserved.