Hubble Space Telescope and Ground-based Observations of Type Ia Supernovae at Redshift 0.5: Cosmological Implications**Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555. This research is primarily associated with proposal GO-7505. ****Based in part on observations taken at the Cerro Tololo Inter-American Observatory. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based in part on observations with the University of Hawaii 2.2 m telescope at Mauna Kea Observatory, Institute for Astronomy, Un
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We present observations of the Type I Supernovae (SNe) 1999M, 1999N, 1999Q, 1999S, and 1999U, at redshiftz z 0.5. They were discovered in early 1999 with the 4.0 m Blanco telescope at Cerro Tololo Inter-American Observatory by the High-z Supernova Search Team (HZT) and subsequently followed with many ground-based telescopes. SNe 1999Q and 1999U were also observed with the Hubble Space Telescope. We computed luminosity distances to the new SNe using two methods and added them to the high-z Hubble diagram that the HZT has been constructing since 1995. The new distance moduli confirm the results of previous work. Atz 0.5, luminosity distances are larger than those expected for an empty universe, implying that a "cosmological constant," or another form of "dark energy," has been increasing the expansion rate of the universe during the last few billion years. Combining these new HZT SNe la with our previous results and assuming a CDM cosmology, we estimate the cosmological parameters that best fit our measurements. For a sample of 75 low-redshift and 47 high-redshift SNe la with MLCS2k2 (Jha and coworkers) luminosity calibration we obtain M = 0.79-0.18+0.15 and = 1.57-0.32+0.24 (1 uncertainties) if no constraints are imposed, or M = 0.29 -0.05+0.06 if M + = 1 is assumed. For a different sample of 58 low-redshift and 48 high-redshift SNe Ia with luminosity calibrations done using the PRES method (a generalization of the m15 method), the results are M = 0.43-0.19+0.17 and = 1-18-0.28+0.27 (1 uncertainties) if no constraints are imposed, or M= 0.18 -0.04+0.05 if M + = 1 is assumed. 2006. The American Astronomical Society. All rights reserved.
