SUPERNOVA CONSTRAINTS AND SYSTEMATIC UNCERTAINTIES FROM THE FIRST THREE YEARS OF THE SUPERNOVA LEGACY SURVEY

Abstract

We combine high redshift Type Ia supernovae from the first 3 years of the\nSupernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at\nlower redshifts, to form a high-quality joint sample of 472 SNe (123 low-$z$,\n93 SDSS, 242 SNLS, and 14 {\\it Hubble Space Telescope}). SN data alone require\ncosmic acceleration at >99.9% confidence, including systematic effects. For the\ndark energy equation of state parameter (assumed constant out to at least\n$z=1.4$) in a flat universe, we find $w = -0.91^{+0.16}_{-0.20}(\\mathrm{stat})\n^{+0.07}_{-0.14} (\\mathrm{sys})$ from SNe only, consistent with a cosmological\nconstant. Our fits include a correction for the recently discovered\nrelationship between host-galaxy mass and SN absolute brightness. We pay\nparticular attention to systematic uncertainties, characterizing them using a\nsystematics covariance matrix that incorporates the redshift dependence of\nthese effects, as well as the shape-luminosity and color-luminosity\nrelationships. Unlike previous work, we include the effects of systematic terms\non the empirical light-curve models. The total systematic uncertainty is\ndominated by calibration terms. We describe how the systematic uncertainties\ncan be reduced with soon to be available improved nearby and\nintermediate-redshift samples, particularly those calibrated onto\nUSNO/SDSS-like systems.\n