Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples^⋆,⋆⋆

¹ LPNHE, CNRS/IN2P3, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, 4 place Jussieu, 75252 Paris Cedex 05, France ;
e-mail: marc.betoule@lpnhe.in2p3.fr
² Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago IL 60637, USA
³ Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue Chicago IL 60637, USA
⁴ LBNL, 1 Cyclotron Rd, Berkeley CA 94720, USA
⁵ Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia PA 19104, USA
⁶ Argonne National Laboratory, 9700 South Cass Avenue, Lemont IL 60439, USA
⁷ Center for Particle Astrophysics, Fermi National Accelerator Laboratory, PO Box 500, Batavia IL 60510, USA
⁸ African Institute for Mathematical Sciences, 6-8 Melrose Road, Muizenberg, Cape Town, South Africa
⁹ South African Astronomical Observatory, Observatory, Cape Town, South Africa
¹⁰ Department of Maths and Applied Maths, University of Cape Town, 7701 Rondebosch, South Africa
¹¹ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A & M University, College Station TX 77843-4242, USA
¹² Institute of Astronomy, Madingley Road, Cambridge CB4 0HA, UK
¹³ Institute of Cosmology & Gravitation, University of Portsmouth, Portsmouth PO1 3FX, UK
¹⁴ Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto ON M5S 3H4, Canada
¹⁵ Department of Physics and Astronomy, Wayne State University, Detroit MI 48202, USA
¹⁶ Center for Astrophysics andSpace Astronomy 389-UCB, University of Colorado, Boulder CO 80309, USA
¹⁷ Institute of Astronomy, Graduate Shool of Science, The Univ. of Tokyo, 2-21-1 Osawa, 181-0015 Mitaka, Japan
¹⁸ Research center for the early universe, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan
¹⁹ Kavli Institute for the Physics and Mathematics of the Universe, 5-1-5 Kashiwanoha, 277-8583 Kashiwa, Japan
²⁰ Department of Astrophysics, California Institute of Technology, MS 249-17, Pasadena CA 91125, USA
²¹ Department of Physics and Astronomy, University of Victoria, PO Box 3055 STN CSC, Victoria BC V8T 1M8, Canada
²² University of California, Berkeley CA 94720, USA
²³ Astronomy Department, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana IL 61801, USA
²⁴ Department of Physics, University of Illinois Urbana-Champaign, 1110 W. Green Street, Urbana IL 61801, USA
²⁵ CPPM, Aix-Marseille Universit, CNRS/IN2P3, Marseille, France
²⁶ Institut de Física d’Altes Energies, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain
²⁷ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
²⁸ The Oskar Klein Centre, Department of Physics, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
²⁹ McDonald Observatory, University of Texas at Austin, 2515 Speedway, Stop C1402, Austin TX 78712-1206, USA
³⁰ Department of Astrophysical Sciences, Princeton University Peyton Hall, 4 Ivy Lane, Princeton NJ 08544, USA
³¹ Department of Physics (Astrophysics), University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
³² INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio (RM), Italy
³³ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta CA 93117, USA
³⁴ Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara CA 93106-9530, USA
³⁵ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway NJ 08854, USA
³⁶ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
³⁷ Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
³⁸ CEA, Centre de Saclay, Irfu/SPP, 91191 Gif-sur-Yvette, France
³⁹ CENTRA – Centro Multidisciplinar de Astrofísica and Dep. Física, Instituto Superior Técnico, Universidade de Lisboa, Portugal
⁴⁰ Department of Physics and Astronomy, University of Utah, Salt Lake City UT 84112, USA
⁴¹ School of Physics and Astronomy, Rochester Institute of Technology, Rochester NY 14623, USA
⁴² Department of Physics and Astronomy, Johns Hopkins University, Baltimore MD 21218, USA
⁴³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA
⁴⁴ Department of Astronomy and Astrophysics and the Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park PA 16802, USA
⁴⁵ Department of Physics, University of the Western Cape, 7535 Cape Town, South Africa
⁴⁶ The Oskar Klein Centre, Department of Astronomy, AlbaNova, 106 91 Stockholm, Sweden
⁴⁷ School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK
⁴⁸ Department of Astronomy, University of Texas at Austin, Austin TX 78712, USA

Received: 13 January 2014
Accepted: 9 April 2014

Abstract

Aims. We present cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The dataset includes several low-redshift samples (z< 0.1), all three seasons from the SDSS-II (0.05 <z< 0.4), and three years from SNLS (0.2 <z< 1), and it totals 740 spectroscopically confirmed type Ia supernovae with high-quality light curves.

Methods. We followed the methods and assumptions of the SNLS three-year data analysis except for the following important improvements: 1) the addition of the full SDSS-II spectroscopically-confirmed SN Ia sample in both the training of the SALT2 light-curve model and in the Hubble diagram analysis (374 SNe); 2) intercalibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis; and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN Ia light curves.

Results. We produce recalibrated SN Ia light curves and associated distances for the SDSS-II and SNLS samples. The large SDSS-II sample provides an effective, independent, low-z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low-z SN sample. For a flat ΛCDM cosmology, we find Ω_m =0.295 ± 0.034 (stat+sys), a value consistent with the most recent cosmic microwave background (CMB) measurement from the Planck and WMAP experiments. Our result is 1.8σ (stat+sys) different than the previously published result of SNLS three-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark-energy equation of state parameter w =−1.018 ± 0.057 (stat+sys) for a flat universe. Adding baryon acoustic oscillation distance measurements gives similar constraints: w =−1.027 ± 0.055. Our supernova measurements provide the most stringent constraints to date on the nature of dark energy.