The DECADE cosmic shear project IV: cosmological constraints from 107 million galaxies across 5,400 deg$^2$ of the sky

TL;DR

The DECADE cosmic shear project analyzes 107 million galaxies over 5,400 deg$^2$ to derive cosmological constraints, demonstrating robust methods that can utilize previously intractable datasets to enhance weak lensing survey power.

Contribution

This work presents the first cosmological constraints from the DECADE dataset, showcasing the effectiveness of cosmic shear analysis on inhomogeneous data and combining results with DES Y3 for improved precision.

Findings

Constraints on $S_8$ and $ m \Omega_m$ consistent with other surveys

Combined data favor $S_8=0.791 \\pm 0.023$

Demonstrates robustness of cosmic shear methods on inhomogeneous datasets

Abstract

We present cosmological constraints from the Dark Energy Camera All Data Everywhere (DECADE) cosmic shear analysis. This work uses shape measurements for 107 million galaxies measured through Dark Energy Camera (DECam) imaging of $5,\!412$ deg$^2$ of sky that is outside the Dark Energy Survey (DES) footprint. We derive constraints on the cosmological parameters $S_8 = 0.791^{+0.027}_{-0.032}$ and $\Omega_{\rm m} =0.269^{+0.034}_{-0.050}$ for the $\Lambda$CDM model, which are consistent with those from other weak lensing surveys and from the cosmic microwave background. We combine our results with cosmic shear results from DES Y3 at the likelihood level, since the two datasets span independent areas on the sky. The combined measurements, which cover $\approx\! 10,\!000$ deg$^2$, prefer $S_8 = 0.791 \pm 0.023$ and $\Omega_{\rm m} = 0.277^{+0.034}_{-0.046}$ under the $\Lambda$CDM model. These results are the culmination of a series of rigorous studies that characterize and validate the DECADE dataset and the associated analysis methodologies (Anbajagane et. al 2025a,b,c). Overall, the DECADE project demonstrates that the cosmic shear analysis methods employed in Stage-III weak lensing surveys can provide robust cosmological constraints for fairly inhomogeneous datasets. This opens the possibility of using data that have been previously categorized as ``unusable'' for cosmic shear analyses, thereby increasing the statistical power of upcoming weak lensing surveys.