The Hubble Space Telescope Cluster Supernova Survey. V. Improving the Darkenergy Constraints above z > 1 and Building an Earlytypehosted Supernova Sample
Abstract
We present Advanced Camera for Surveys, NICMOS, and Keck adaptiveopticsassisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Of these SNe Ia, 14 pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Of our new SNe Ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of HSTdiscovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zero point at the count rates appropriate for very distant SNe Ia. Adding these SNe improves the best combined constraint on darkenergy density, ρ_{DE}(z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat ΛCDM universe, we find Ω_{Λ} = 0.729 ± 0.014 (68% confidence level (CL) including systematic errors). For a flat wCDM model, we measure a constant darkenergy equationofstate parameter w = 1.013^{+0.068} _{0.073} (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark energy is allowed to vary with parameters w _{0} and w_{a} . Further tightening the constraints on the time evolution of dark energy will require several improvements, including highquality multipassband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union.
Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 526555. The observations are associated with program GO10496.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 2012
 DOI:
 10.1088/0004637X/746/1/85
 arXiv:
 arXiv:1105.3470
 Bibcode:
 2012ApJ...746...85S
 Keywords:

 cosmological parameters;
 distance scale;
 supernovae: general;
 Astrophysics  Cosmology and Extragalactic Astrophysics
 EPrint:
 27 pages, 11 figures. Submitted to ApJ. This first posting includes updates in response to comments from the referee. See http://www.supernova.lbl.gov for other papers in the series pertaining to the HST Cluster SN Survey. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union