Dark Energy Survey Year 3 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing

We present the first cosmology results from large-scale structure in the Dark Energy Survey (DES) spanning 5000 deg$^2$. We perform an analysis combining three two-point correlation functions (3$\times$2pt): (i) cosmic shear using 100 million source galaxies, (ii) galaxy clustering, and (iii) the cross-correlation of source galaxy shear with lens galaxy positions. The analysis was designed to mitigate confirmation or observer bias; we describe specific changes made to the lens galaxy sample following unblinding of the results. We model the data within the flat $\Lambda$CDM and $w$CDM cosmological models. We find consistent cosmological results between the three two-point correlation functions; their combination yields clustering amplitude $S_8=0.776^{+0.017}{-0.017}$ and matter density $\Omega{\mathrm{m}} = 0.339^{+0.032}{-0.031}$ in $\Lambda$CDM, mean with 68% confidence limits; $S_8=0.775^{+0.026}{-0.024}$, $\Omega_{\mathrm{m}} = 0.352^{+0.035}{-0.041}$, and dark energy equation-of-state parameter $w=-0.98^{+0.32}{-0.20}$ in $w$CDM. This combination of DES data is consistent with the prediction of the model favored by the Planck 2018 cosmic microwave background (CMB) primary anisotropy data, which is quantified with a probability-to-exceed $p=0.13$ to $0.48$. When combining DES 3$\times$2pt data with available baryon acoustic oscillation, redshift-space distortion, and type Ia supernovae data, we find $p=0.34$. Combining all of these data sets with Planck CMB lensing yields joint parameter constraints of $S_8 = 0.812^{+0.008}{-0.008}$, $\Omega{\mathrm{m}} = 0.306^{+0.004}{-0.005}$, $h=0.680^{+0.004}{-0.003}$, and $\sum m_{\nu}<0.13 ;\mathrm{eV; (95% ;CL)}$ in $\Lambda$CDM; $S_8 = 0.812^{+0.008}{-0.008}$, $\Omega{\mathrm{m}} = 0.302^{+0.006}{-0.006}$, $h=0.687^{+0.006}{-0.007}$, and $w=-1.031^{+0.030}_{-0.027}$ in $w$CDM. (abridged)