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

## Abstract

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)

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### Scholars@Duke

#### Daniel M. Scolnic

Use observational tools to measure the expansion history of the universe. Trying to answer big questions like 'what is dark energy?'.

#### Michael A. Troxel

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