SPECTRA AND<i>HUBBLE SPACE TELESCOPE</i>LIGHT CURVES OF SIX TYPE Ia SUPERNOVAE AT 0.511 &lt;<i>z</i>&lt; 1.12 AND THE UNION2 COMPILATION

Abstract

We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise HST data, and spectra of six SNe Ia that were discovered during 2001 are presented. Additionally, for the two SNe with z>1, we present ground-based J-band photometry from Gemini and the VLT. These are among the most distant SNe Ia for which ground based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation (Kowalski et al. 2008). We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 supernovae, the Union2 compilation. The flat concordance LambdaCDM model remains an excellent fit to the Union2 data with the best fit constant equation of state parameter w=-0.997^{+0.050}_{-0.054} (stat) ^{+0.077}_{-0.082} (stat+sys\ together) for a flat universe, or w=-1.035^{+0.055}_{-0.059} (stat)^{+0.093}_{-0.097} (stat+sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depend strongly on redshift. In particular, at z > 1, the existence and nature of dark energy are only weakly constrained by the data.

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Affiliated Institutions

• University of California, Berkeley US
• Texas A&M University US
• Université Paris Cité FR
• University of Utah US
• Lawrence Berkeley National Laboratory US
• Sorbonne Université FR
• Space Telescope Science Institute US
• AlbaNova SE
• Carnegie Observatories US
• Laboratoire de Physique Nucléaire et de Hautes Énergies FR
• University of Bonn DE
• University of Oxford GB
• Stockholm University SE
• University of Victoria CA
• Centre National de la Recherche Scientifique FR
• Laboratory for Atmospheric and Space Physics US
• University of Pittsburgh US
• Osservatorio Astrofisico di Catania IT
• Las Cumbres Observatory Global Telescope Network US
• Astronomical Observatory of Rome IT
• University of California, Santa Barbara US
• Universitat de Barcelona ES
• Colorado College US
• The University of Tokyo JP
• National Astronomical Observatory of Japan JP
• Université Bourgogne Franche-Comté FR

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