We present a new compilation of Type Ia supernovae ( SNe Ia ) , a new dataset of low-redshift nearby-Hubble-flow SNe and new analysis procedures to work with these heterogeneous compilations .
This “ Union ” compilation of 414 SN Ia , which reduces to 307 SNe after selection cuts , includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey , the older datasets , as well as the recently extended dataset of distant supernovae observed with HST .
A single , consistent and blind analysis procedure is used for all the various SN Ia subsamples , and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers .
We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements ( CMB and BAO ) .
The constraint we obtain from supernovae on the dark energy density is \Omega _ { \Lambda } = 0.713 ^ { +0.027 } _ { -0.029 } { ( stat ) } ^ { +0.036 } _ { -0.039 } { ( sys ) } , for a flat , \Lambda CDM Universe .
Assuming a constant equation of state parameter , w , the combined constraints from SNe , BAO and CMB give w = -0.969 ^ { +0.059 } _ { -0.063 } { ( stat ) } ^ { +0.063 } _ { -0.066 } { ( sys ) } .
While our results are consistent with a cosmological constant , we obtain only relatively weak constraints on a w that varies with redshift .
In particular , the current SN data do not yet significantly constrain w at z > 1 .
With the addition of our new nearby Hubble-flow SNe Ia , these resulting cosmological constraints are currently the tightest available .