Dark Energy Survey Year 3 results: cosmological constraints from galaxy clustering and weak lensing

We present the first cosmology results fromlarge-scale structure usingthe full 5000 deg2 ofimaging data from the Dark Energy Survey (DES) Data Release 1. We perform an analysis of large-scale structure combining three two-point correlation functions (3 × 2pt): (i) cosmic shear using 100 million source galaxies, (ii) galaxy clustering, and (iii)the cross-correlation of source galaxy shear withlens galaxy positions, galaxy–galaxylensing. To achievethe cosmological precisionenabled bythesemeasurements has required updatesto nearly every part of the analysis from DES Year 1, including the use of two independent galaxy clustering samples, modeling advances, and several novel improvements in the calibration of gravitational shear and photometric redshift inference. The analysis was performed under strict conditions to mitigate confirmation or observer bias; we describe specific changes made to the lens galaxy sample following unblinding of the results and tests of the robustness of our results to this decision. We model the data within the flat ΛCDM and wCDM cosmological models, marginalizing over 25 nuisance parameters. We find consistent cosmological results between the three two-point correlation functions; their combination yields clustering amplitude S8 ¼ 0.776þ0.017 −0.017 and matter density Ωm ¼ 0.339þ0.032 −0.031 in ΛCDM, mean with 68% confidence limits; S8 ¼ 0.775þ0.026 −0.024 , Ωm ¼ 0.352þ0.035 −0.041 , and dark energy equation-of-state parameter w ¼ −0.98þ0.32 −0.20 in wCDM. These constraints correspond to an improvementin signal-to-noise oftheDESYear 33 × 2pt data relativetoDESYear 1 by a factor of 2.1,about 20% morethan expected fromtheincreasein observing area alone.This combination ofDES datais consistent withthe prediction of the model favored by the Planck 2018 cosmic microwave background (CMB) primary anisotropy data, which is quantified with a probability-to-exceed p ¼ 0.13–0.48. We find better agreement between DES 3 × 2pt and Planck than in DES Y1, despite the significantly improved precision of both.When combining DES 3 × 2pt data with available baryon acoustic oscillation, redshift-space distortion, and type Ia supernovae data, we find p ¼ 0.34. Combining all of these datasets with Planck CMB lensing yields joint parameter constraints of S8 ¼ 0.812þ0.008 −0.008 , Ωm ¼ 0.306þ0.004 −0.005 , h ¼ 0.680þ0.004 −0.003 , and Pmν < 0.13 eV (95% C.L.) in ΛCDM; S8 ¼ 0.812þ0.008 −0.008 , Ωm ¼ 0.302þ0.006 −0.006 , h ¼ 0.687þ0.006 −0.007 , and w ¼ −1.031þ0.030 −0.027 in wCDM.