Lensing Bias in Cosmic Shear

TL;DR

Lensing bias occurs in cosmic shear measurements because gravitational lensing can change galaxy brightness and size, leading to biased cosmological parameter estimates if uncorrected, especially in Stage III experiments like DES.

Contribution

This paper quantifies the impact of lensing bias on cosmic shear measurements and highlights the necessity of correction for accurate cosmological inference.

Findings

Lensing bias significantly affects shear power spectrum estimates.

Uncorrected bias can lead to 2-3 sigma errors in cosmological parameters.

The effect is particularly relevant for Stage III surveys like DES.

Abstract

Only galaxies bright enough and large enough to be unambiguously identified and measured are included in galaxy surveys used to estimate cosmic shear. We demonstrate that because gravitational lensing can scatter galaxies across the brightness and size thresholds, cosmic shear experiments suffer from lensing bias. We calculate the effect on the shear power spectrum and show that - unless corrected for - it will lead analysts to cosmological parameters estimates that are biased at the 2-3\sigma level in DETF Stage III experiments, such as the Dark Energy Survey.