Dark Energy Survey Year 3: Blue Shear

TL;DR

This paper demonstrates that selecting blue, star-forming galaxies for weak lensing reduces the impact of intrinsic galaxy alignments, leading to more stable cosmological constraints and improved model fit.

Contribution

It shows that sample selection based on galaxy color can effectively mitigate intrinsic alignments in cosmic shear analyses, improving cosmological parameter estimation.

Findings

Cosmological constraints from blue galaxies are stable against IA model variations.

Sample selection reduces IA impact, decreasing $S_8$ uncertainty by 1.5 times.

Goodness-of-fit is improved when using blue galaxy samples.

Abstract

Modeling the intrinsic alignment (IA) of galaxies poses a challenge to weak lensing analyses. The Dark Energy Survey is expected to be less impacted by IA when limited to blue, star-forming galaxies. The cosmological parameter constraints from this blue cosmic shear sample are stable to IA model choice, unlike passive galaxies in the full DES Y3 sample, the goodness-of-fit is improved and the $\Omega_{m}$ and $S_8$ better agree with the cosmic microwave background. Mitigating IA with sample selection, instead of flexible model choices, can reduce uncertainty in $S_8$ by a factor of 1.5.