Emulating redshift mixing due to blending in weak gravitational lensing

TL;DR

This paper introduces a novel simulation-based method to correct for redshift mixing caused by blending in weak gravitational lensing, improving the accuracy of shear measurements in cosmology.

Contribution

The authors develop a new emulation technique for shear response to neighboring galaxies, enabling correction of redshift distribution biases due to blending in weak lensing analyses.

Findings

Effective redshift bias reduced by approximately 0.05 when correction is applied.

Method validated under various observing conditions and galaxy populations.

Simulation approach is compatible with future cosmological data analyses.

Abstract

Galaxies whose images overlap in the focal plane of a telescope, commonly referred to as blends, are often located at different redshifts. Blending introduces a challenge to weak-lensing cosmology probes since such blends are subject to shear signals from multiple redshifts. This effect can be described by joining shear bias and redshift characterisation in the effective redshift distribution, $n_{\gamma}(z)$, which includes the response of apparent shapes of detected objects to shear of galaxies at redshift, $z$. In this work, we propose a novel method to correct $n_{\gamma}(z)$ for redshift-mixed blending by emulating the shear response to neighbouring galaxies. We designed a `half-sky-shearing' simulation with Subaru Hyper Suprime Cam (HSC) wide-like specifications, which allowed us to extract the response of a detected object's measured ellipticity to the shearing of neighbouring galaxies among numerous galaxy pairs. We demonstrate the feasibility of accurately emulating these pairwise responses and validate the robustness of our approach under varying observing conditions and galaxy population uncertainties. We find that the effective redshift of sources at the high-redshift tail of the distribution is about 0.05 lower than expected when the effect is not modelled. Given adequately processed image simulations, our correction method can be readily incorporated into future cosmological analyses to mitigate this source of systematic error.