We combine high redshift Type Ia supernovae from the first 3 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 } \left ( \mathrm { stat } \right ) ^ { +0.07 } _ { -0.14 } \left ( \mathrm% { sys } \right ) 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 systematics 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 .