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

TL;DR

DECADE addresses the tension between weak-lensing and CMB constraints by delivering independent cosmological constraints from a large, independent cosmic shear dataset outside the DES footprint. The analysis follows a DES Y3–style pipeline, employing Metacalibration for shear estimation, SOMPZ redshift calibration, and a TATT intrinsic alignment model while marginalizing over baryonic effects with HMCode. The results show $S_8$ and $\Omega_m$ consistent with Planck within about $1$–$1.5\sigma$, and the combined DECADE+DES Y3 data improve the precision on $S_8$ by roughly 26% compared to the individual surveys. The work demonstrates that Stage-III lensing methodologies can yield robust cosmological constraints on datasets with substantial inhomogeneity and highlights IA and small-scale modeling as critical areas for future improvement.

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 $Ω_{\rm m} =0.269^{+0.034}_{-0.050}$ for the $Λ$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 $Ω_{\rm m} = 0.277^{+0.034}_{-0.046}$ under the $Λ$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.

Figures (13)

• Figure 1: The footprint of the DECADE cosmic shear analysis, in relation to those of three other Stage-III surveys: DES Y3 (grey), KiDS-1000 (dark blue), and HSC Y3 (purple). We also show the footprints for the LSST wide-field survey (black solid), the Euclid wide-field survey (black dotted), the SPT Ext-10k survey (orange), and ACT DR6 (yellow). See the introduction for references to the different experiments.
• Figure 2: Redshift distributions, $n(z)$, for the four tomographic bins defined in the source galaxy sample. We show both the fiducial redshift distributions derived from the SOMPZ method and also those from combining SOMPZ with information from the clustering redshift (WZ) method [see Section 3.7 of][]paper2.
• Figure 3: Our cosmic shear data vector and best-fit predictions under a $\Lambda$CDM and wCDM model. The upper (lower) triangle shows the $\xi_+$ ($\xi_-$) data vectors. Each panel corresponds to a bin pair, denoted in the legend. The shaded region marks angular scales removed during inference due to uncertainty in modeling baryonic effects in the matter power spectra. We show normalized residuals, $\delta \xi_\pm = (\xi^{\rm\, data}_\pm - \xi^{\rm\, theory}_\pm)/\sigma_{\xi_\pm}$, in the lower sub-panel for each bin pair. The horizontal gray band covers the 1$\sigma$ region around $\delta \xi_\pm = 0$.
• Figure 4: The fiducial $\Lambda$CDM cosmic shear constraints for $\Omega_{\rm m}$ and $S_8$. The $\star$ denotes constraints reanalysed using our pipeline. All constraints are also listed in Table \ref{['tab:constraints']}. Left: Results from DECADE (red), DES Y3 analyzed with our pipeline (black solid), the combination of the two (blue), and Planck (black dashed). The DECADE data constrains $S_8=0.791^{+0.027}_{-0.032}$, which is consistent with DES Y3 and also has similar constraining power to DES Y3 when both are analyzed with the same pipeline. The $S_8$ constraints from DECADE (DECADE + DES Y3) are consistent with Planck within the $1.1\sigma$ ($1.2\sigma$) level. Right: Comparison of the DECADE constraints with other published results. We do not reanalyze any data in this case and use the public posteriors. The DECADE results are consistent with existing constraints within $\lesssim 1 \sigma$. See Section \ref{['sec:sec:Consistency']} for references and links to the chains from the other lensing surveys.
• Figure 5: Cosmic shear constraints under a $w$CDM model, for $\Omega_{\rm m}$, $S_8$ and $w$ for DECADE (red), DES Y3 (black solid), the combination of DECADE and DES y3 (blue), and Planck (black dashed). The constraint from DECADE (DECADE + DES Y3) is $w = -1.47^{+0.41}_{-0.25}$ ($w = -1.57^{+0.38}_{-0.16}$), which is consistent with Planck and with the $\Lambda$CDM expectation of $w = -1$ (dotted gray line). The DES Y3 data was reanalyzed using our pipeline. All presented constraints are listed in Table \ref{['tab:constraints']}.