Dark Energy Survey Year 6 Results: Weak Lensing and Galaxy Clustering Cosmological Analysis Framework

TL;DR

This paper develops and validates a comprehensive analysis framework for weak lensing and galaxy clustering data from DES Year 6, enabling unbiased cosmological constraints while accounting for key theoretical uncertainties.

Contribution

It introduces a validated, robust analysis pipeline for cosmic shear, galaxy clustering, and their combination, incorporating systematic uncertainties and scale cuts for DES Year 6 data.

Findings

Validated analysis pipelines for cosmic shear and galaxy clustering.

Confirmed unbiased cosmological constraints with mock data.

Provided a framework applicable to future surveys like LSST.

Abstract

We present the methodology for the weak lensing and galaxy clustering analyses of the Dark Energy Survey (DES) Year 6 data set. In this work, we design and validate the analysis pipeline for the cosmic shear, galaxy clustering plus galaxy$-$galaxy lensing ($2 \times 2$pt), and the joint analysis in the $3 \times 2$pt. Our framework accounts for key theoretical uncertainties, such as baryonic feedback and galaxy bias, incorporating both linear and non-linear models. We apply scale cuts in regimes where theoretical modeling becomes unreliable. The robustness of the pipeline is validated using mock data and simulations, confirming unbiased cosmological constraints and highlighting the importance of posterior projection effects in the validation process. As a result, we deliver robust and validated analysis pipelines for cosmic shear, $2 \times 2$pt, and $3 \times 2$pt in $\Lambda$CDM and $w$CDM scenarios, including a well-defined set of scales suitable for real data analysis, a robust prescription for theoretical systematics, and the theoretical covariance of the signal. This comprehensive methodology also lays the groundwork for future galaxy surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time.