The Dark Energy Camera All Data Everywhere cosmic shear project V: Constraints on cosmology and astrophysics from 270 million galaxies across 13,000 deg$^2$ of the sky

TL;DR

This study leverages the largest weak-lensing dataset to date by combining DECADE (NGC+SGC) with DES Y3 over 13,000 deg$^2$ and 270 million galaxies to constrain $\Lambda$CDM, dynamical dark energy, and baryon-feedback models. It uses HMCode-based nonlinear matter power spectra and a flexible intrinsic alignment model in a Bayesian framework, incorporating a comprehensive covariance and external data (DESI DR2 BAO and DES SNe) where applicable. The results show LCDM compatibility with Planck at the few-sigma level and reveal that dynamical dark energy constraints improve modestly with lensing, while multiple baryon-modeling approaches yield consistent suppression signals when priors are wide enough; scale cuts mitigate biases to $\sim 0.3\sigma$, and small-scale information primarily helps self-calibrate baryon models rather than sharply tightening cosmology. The work underscores the complementarity of lensing with external probes for small-scale physics and provides a data/product release to catalyze further multi-probe cosmology.

Abstract

We present constraints on models of cosmology and astrophysics using cosmic shear data vectors from three datasets: the northern and southern Galactic cap of the Dark Energy Camera All Data Everywhere (DECADE) project, and the Dark Energy Survey (DES) Year 3. These data vectors combined consist of 270 million galaxies spread across 13,000 ${\rm deg}^2$ of the sky. We first extract constraints for $Λ$CDM cosmology and find $S_8= 0.805^{+0.019}_{-0.019}$ and $Ω_{\rm m} = 0.262^{+0.023}_{-0.036}$, which is consistent within $1.9 σ$ of constraints from the Planck satellite. Extending our analysis to dynamical dark energy models shows that lensing provides some (but still minor) improvements to existing constraints from supernovae and baryon acoustic oscillations. Finally, we study six different models for the impact of baryons on the matter power spectrum. We show the different models provide consistent constraints on baryon suppression, and associated cosmology, once the astrophysical priors are sufficiently wide. Current scale-cut approaches for mitigating baryon contamination result in a residual bias of $\approx 0.3σ$ in the $S_8, Ω_{\rm m}$ posterior. Using all scales with dedicated baryon modeling leads to negligible improvement as the new information is used solely to self-calibrate the baryon model on small scales. Additional non-lensing datasets, and/or calibrations of the baryon model, will be required to access the full statistical power of the lensing measurements. The combined dataset in this work represents the largest lensing dataset to date (most galaxies, largest area) and provides an apt testing ground for analyses of upcoming datasets from Stage IV surveys. The DECADE shear catalogs, data vectors, and likelihoods are made publicly available.

Figures (16)

• Figure 1: The footprint of the DECADE cosmic shear analysis (light blue), in relation to those from other surveys. Reproduced from Figure 1 of paper4, but now presenting the DECADE SGC region as well. We show three other Stage-III surveys: DES Y3 (grey), KiDS-1000 (dark blue), and HSC Y3 (purple), and 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 Section \ref{['sec:data_methods']} for references to the different experiments.
• Figure 2: The $\Lambda$CDM constraints from DECADE and DES Y3. We refer to the combination of DECADE NGC, DECADE SGC, and DES Y3 as "DECam 13k", and that of just DECADE NGC and DES Y3 as "DECam 10k". We show the latter for easier comparisons with the results of paper4 and to highlight the improvement from the inclusion of the DECADE SGC data. The full 13,000 $\deg^2$ (13k) dataset has a Figure of Merit that improves by three times over the DES Y3-only result (Table \ref{['tab:constraints']}). The combination with external data (DESI DR2 BAO and DES Y5 SNe) constrains $\Omega_{\rm m}$ and prefers lower values of $S_8$, which are still consistent with the posterior of the 13k shear-only analysis.
• Figure 3: The constraints on two dynamical dark energy models --- the phenomological $w_0w_a$ model (left) and a first-principles scalar field model from Shajib:2025:wphi (right). In both cases, the combination of cosmic shear plus BAO does not find any deviation from $\Lambda$CDM, while combining BAO and SNe does show deviations. Adding lensing to this latter combination marginally improves the constraints. See Table \ref{['tab:dynamDE']} for numerical values.
• Figure 4: The baryonic suppression at $z = 0$ from the different models. We show three popular methods --- BCEmu, Bacco, and HMx. For each, we provide a version obtained from a halo-model calculation using the BaryonForge pipeline. See text for details. The black dotted line in each panel is the BCEmu result for the DECam 13k dataset, shown as reference. In general, the BCEmu-derived matter power suppression is stronger than those from the other models. However, concordance can be achieved by adequately widening the priors of the other models (the models tagged with "Wide" in the above plot). See Appendix \ref{['appx:BaryonModel']} for more details on the modeling and the choice of priors. The BFG-BCEmu results matches the BCEmu result if the former adopts the narrower cosmology priors of the latter (Figure \ref{['fig:Testfixcosmo']}). The inclusion of external data, from DESI DR2 BAO and DES Y5 SNe (bottom), provides results that are consistent with the fiducial case.
• Figure 5: The $\Lambda$CDM constraints from (i) using our fiducial model ("No baryons") or one that includes baryon power suppression ("BCEmu") and (ii) using a data vector with all scales or with scale cuts. The constraints from including the baryon modeling (with and without scale cuts) is consistent with those from the fiducial model with scale cuts. The results indicate that after scale cuts are applied, the residual bias is $0.3\sigma$ in the $S_8$-$\Omega_{\rm m}$ plane. Using all scales with an explicit baryon model has a 6% higher FoM compared to using scale cuts with no baryon model. See Section \ref{['sec:Baryons']} for more discussion.