We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing , using 1321 deg ^ { 2 } of griz imaging data from the first year of the Dark Energy Survey ( DES Y1 ) .
We combine three two-point functions : ( i ) the cosmic shear correlation function of 26 million source galaxies in four redshift bins , ( ii ) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins , and ( iii ) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears .
To demonstrate the robustness of these results , we use independent pairs of galaxy shape , photometric redshift estimation and validation , and likelihood analysis pipelines .
To prevent confirmation bias , the bulk of the analysis was carried out while ‘ ‘ blind ’ ’ to the true results ; we describe an extensive suite of systematics checks performed and passed during this blinded phase .
The data are modeled in flat \Lambda CDM and w CDM cosmologies , marginalizing over 20 nuisance parameters , varying 6 ( for \Lambda CDM ) or 7 ( for w CDM ) cosmological parameters including the neutrino mass density and including the 457 \times 457 element analytic covariance matrix .
We find consistent cosmological results from these three two-point functions , and from their combination obtain S _ { 8 } \equiv \sigma _ { 8 } ( \Omega _ { m } / 0.3 ) ^ { 0.5 } = 0.773 ^ { +0.026 } _ { -0.020 } and \Omega _ { m } = 0.267 ^ { +0.030 } _ { -0.017 } for \Lambda CDM ; for w CDM , we find S _ { 8 } = 0.782 ^ { +0.036 } _ { -0.024 } , \Omega _ { m } = 0.284 ^ { +0.033 } _ { -0.030 } , and w = -0.82 ^ { +0.21 } _ { -0.20 } at 68 % CL .
The precision of these DES Y1 constraints rivals that from the Planck cosmic microwave background measurements , allowing a comparison of structure in the very early and late Universe on equal terms .
Although the DES Y1 best-fit values for S _ { 8 } and \Omega _ { m } are lower than the central values from Planck for both \Lambda CDM and w CDM , the Bayes factor indicates that the DES Y1 and Planck data sets are consistent with each other in the context of \Lambda CDM .
Combining DES Y1 with Planck , Baryonic Acoustic Oscillation measurements from SDSS , 6dF , and BOSS , and type Ia supernovae from the Joint Lightcurve Analysis ( JLA ) dataset , we derive very tight constraints on cosmological parameters : S _ { 8 } = 0.802 \pm 0.012 and \Omega _ { m } = 0.298 \pm 0.007 in \Lambda CDM , and w = -1.00 _ { -0.04 } ^ { +0.05 } in w CDM .
Upcoming DES analyses will provide more stringent tests of the \Lambda CDM model and extensions such as a time-varying equation of state of dark energy or modified gravity .