Strong gravitational lenses with measured time delays between the multiple images and models of the lens mass distribution allow a one-step determination of the time-delay distance , and thus a measure of cosmological parameters .
We present a blind analysis of the gravitational lens RXJ1131 - 1231 incorporating ( 1 ) the newly measured time delays from COSMOGRAIL , the COSmological MOnitoring of GRAvItational Lenses , ( 2 ) archival Hubble Space Telescope imaging of the lens system , ( 3 ) a new velocity-dispersion measurement of the lens galaxy of 323 \pm 20 km s ^ { -1 } based on Keck spectroscopy , and ( 4 ) a characterization of the line-of-sight structures via observations of the lens ’ environment and ray tracing through the Millennium Simulation .
Our blind analysis is designed to prevent experimenter bias .
The joint analysis of the data sets allows a time-delay distance measurement to 6 % precision that takes into account all known systematic uncertainties .
In combination with the Wilkinson Microwave Anisotropy Probe seven-year ( WMAP7 ) data set in flat w CDM cosmology , our unblinded cosmological constraints for RXJ1131 - 1231 are : H _ { 0 } = 80.0 ^ { +5.8 } _ { -5.7 } km s ^ { -1 } Mpc ^ { -1 } , \Omega _ { de } = 0.79 \pm 0.03 , w = -1.25 ^ { +0.17 } _ { -0.21 } .
We find the results to be statistically consistent with those from the analysis of the gravitational lens B1608 + 656 , permitting us to combine the inferences from these two lenses .
The joint constraints from the two lenses and WMAP7 are H _ { 0 } = 75.2 ^ { +4.4 } _ { -4.2 } km s ^ { -1 } Mpc ^ { -1 } , \Omega _ { de } = 0.76 ^ { +0.02 } _ { -0.03 } and w = -1.14 ^ { +0.17 } _ { -0.20 } in flat w CDM , and H _ { 0 } = 73.1 ^ { +2.4 } _ { -3.6 } km s ^ { -1 } Mpc ^ { -1 } , \Omega _ { \Lambda } = 0.75 ^ { +0.01 } _ { -0.02 } and \Omega _ { k } = 0.003 ^ { +0.005 } _ { -0.006 } in open \Lambda CDM .
Time-delay lenses constrain especially tightly the Hubble constant H _ { 0 } ( 5.7 % and 4.0 % respectively in w CDM and open \Lambda CDM ) and curvature of the universe .
The overall information content is similar to that of Baryon Acoustic Oscillation experiments .
Thus , they complement well other cosmological probes , and provide an independent check of unknown systematics .
Our measurement of the Hubble constant is completely independent of those based on the local distance ladder method , providing an important consistency check of the standard cosmological model and of general relativity .