Browsing by Subject "anisotropies"

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    Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples
    (2014) Betoule, M; Kessler, R; Guy, J; Mosher, J; Hardin, D; Biswas, R; Astier, P; El-Hage, P; Konig, M; Kuhlmann, S; Marriner, J; Pain, R; Regnault, N; Balland, C; Bassett, B A; Brown, P J; Campbell, H; Carlberg, R G; Cellier-Holzem, F; Cinabro, D; Conley, A; D’Andrea, C B; DePoy, D L; Doi, M; Ellis, R S; Fabbro, S; Filippenko, A V; Foley, R J; Frieman, J A; Fouchez, D; Galbany, L; Goobar, A
    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 eective, 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 CDM cosmology, we find 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 1:8 (stat+sys) dierent 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 = ?1:0270:055. Our supernova measurements provide the most stringent constraints to date on the nature of dark energy.