Dark Energy Survey Year 6 Results: Point-spread Function Modeling

TL;DR

This paper details the improvements in PSF modeling for weak lensing analysis using six years of DES data, including new techniques like color-dependent modeling and diagnostics, resulting in reduced systematic errors.

Contribution

Introduces novel PSF modeling enhancements such as color dependence and diagnostics, improving accuracy for weak lensing in DES Y6 data.

Findings

Significantly smaller systematic errors in Y6 PSF models compared to Y3.

Inclusion of g band data improves photometric redshift estimation.

Enhanced diagnostics reveal reduced biases in PSF modeling.

Abstract

We present the point-spread function (PSF) modeling for weak lensing shear measurement using the full six years of the Dark Energy Survey (DES Y6) data. We review the PSF estimation procedure using the PIFF (PSFs In the Full FOV) software package and describe the key improvements made to PIFF and modeling diagnostics since the DES year three (Y3) analysis: (i) use of external Gaia and infrared photometry catalogs to ensure higher purity of the stellar sample used for model fitting, (ii) addition of color-dependent PSF modeling, the first for any weak lensing analysis, and (iii) inclusion of model diagnostics inspecting fourth-order moments, which can bias weak lensing measurements to a similar degree as second-order modeling errors. Through a comprehensive set of diagnostic tests, we demonstrate the improved accuracy of the Y6 models evident in significantly smaller systematic errors than those of the Y3 analysis, in which all $g$ band data were excluded due to insufficiently accurate PSF models. For the Y6 weak lensing analysis, we include $g$ band photometry data in addition to the $riz$ bands, providing a fourth band for photometric redshift estimation. Looking forward to the next generation of wide-field surveys, we describe several ongoing improvements to PIFF, which will be the default PSF modeling software for weak lensing analyses for the Vera C. Rubin Observatory's Legacy Survey of Space and Time.