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Published January 2011 | Published
Journal Article Open

Supernova Constraints and Systematic Uncertainties from the First Three Years of the Supernova Legacy Survey


We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = –0.91^(+0.16)_(–0.20)(stat)^(+0.07)_(–0.14)(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems.

Additional Information

© 2011 American Astronomical Society. Received 2010 August 6; accepted 2010 October 22; published 2010 December 13. The SNLS collaboration gratefully acknowledges the assistance of Pierre Martin and the CFHT Queued Service Observations team. Jean-Charles Cuillandre and Kanoa Withington were also indispensable in making possible real-time data reduction at CFHT. This work is based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at the Canadian Astronomy Data Centre as part of the CFHT Legacy Survey, a collaborative project of NRC and CNRS. Canadian collaboration members acknowledge support fromNSERC and CIAR, French collaboration members from CNRS/IN2P3, CNRS/INSU and CEA, and Portugese members from Funda¸cao para a Ciencia e Tecnologia. We thank D. J. Schlegel for making the updated SDSS calibration available to us prior to publication, and A. Riess, A. Landolt, and R. Kessler for many useful discussions. M. Hicken provided useful feedback about the CfAIII SN sample. We thank R. Bohlin for helping us understand the uncertainties in the STIS SED of Vega, and R. de Jong for clarifying the NICMOS nonlinearity corrections. Finally, we thank the anonymous referee, whose extremely thoughtful and thorough comments greatly improved this paper. Facilities: CFHT (MegaCam), Gemini:Gillett (GMOS-N), Gemini:South (GMOS-S), Keck:I (LRIS), VLT:Antu (FORS2), VLT:Kueyen (FORS1)

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