We report measurements of \Omega _ { \mathrm { M } } , \Omega _ { \Lambda } , and w from eleven supernovae at z = 0.36 – 0.86 with high-quality lightcurves measured using WFPC2 on the HST .
This is an independent set of high-redshift supernovae that confirms previous supernova evidence for an accelerating Universe .
The high-quality lightcurves available from photometry on WFPC2 make it possible for these eleven supernovae alone to provide measurements of the cosmological parameters comparable in statistical weight to the previous results .
Combined with earlier Supernova Cosmology Project data , the new supernovae yield a measurement of the mass density \Omega _ { \mathrm { M } } = 0.25 ^ { +0.07 } _ { -0.06 } ( statistical ) \pm 0.04 ( identified systematics ) , or equivalently , a cosmological constant of \Omega _ { \Lambda } = 0.75 ^ { +0.06 } _ { -0.07 } ( statistical ) \pm 0.04 ( identified systematics ) , under the assumptions of a flat universe and that the dark energy equation of state parameter has a constant value w = -1 .
When the supernova results are combined with independent flat-universe measurements of \Omega _ { \mathrm { M } } from CMB and galaxy redshift distortion data , they provide a measurement of w = -1.05 ^ { +0.15 } _ { -0.20 } ( statistical ) \pm 0.09 ( identified systematic ) , if w is assumed to be constant in time .
In addition to high-precision lightcurve measurements , the new data offer greatly improved color measurements of the high-redshift supernovae , and hence improved host-galaxy extinction estimates .
These extinction measurements show no anomalous negative E ( B - V ) at high redshift .
The precision of the measurements is such that it is possible to perform a host-galaxy extinction correction directly for individual supernovae without any assumptions or priors on the parent E ( B - V ) distribution .
Our cosmological fits using full extinction corrections confirm that dark energy is required with P ( \Omega _ { \Lambda } > 0 ) > 0.99 , a result consistent with previous and current supernova analyses which rely upon the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution .