Implications For The Hubble Constant from the First SevenSupernovae at z

The Supernova Cosmology Project has discovered over twenty-eight supernovae (SNe) at 0:35 < z < 0:65 in an ongoing program that uses Type Ia SNe as high-redshift distance indicators. Here we present measurements of the ratio between the locally observed and global Hubble constants, H L 0 =H G 0 , based on the rst 7 SNe of this high-redshift data set compared with 18 SNe at z 0:1 from the Call an/Tololo survey. If M 2, then light-curve-width corrected SN magnitudes yield H L 0 =H G 0 < 1:20 (95% conndence level) in a = 0 universe and H L 0 =H G 0 < 1:27 in a at universe. The analysis using the SNe Ia 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 SNe Ia of Sandage et al. (1996), we can also measure the global Hubble constant, H G 0. Independent of M , we nd that H G 0 < 71 km s ?1 Mpc ?1 in a = 0 universe and H G 0 < 83 km s ?1 Mpc ?1 in a at universe, correcting the distant and local SN apparent magnitudes for light curve width. Lower results for H G 0 are obtained if the magnitudes are not width corrected.