Measurement and Calibration of Noise Bias in Weak Lensing Galaxy Shape Estimation

TL;DR

This paper investigates how pixel noise impacts shear bias in weak lensing galaxy shape estimation, demonstrating a calibration method that significantly reduces bias to meet future survey accuracy requirements.

Contribution

It introduces a simulation-based calibration approach to correct noise-induced shear biases in maximum-likelihood galaxy shape measurements.

Findings

Noise can cause 1-10% shear bias in measurements.

Calibration reduces bias to acceptable levels for upcoming surveys.

Method improves the accuracy of weak lensing shear estimates.

Abstract

Weak gravitational lensing has the potential to constrain cosmological parameters to high precision. However, as shown by the Shear TEsting Programmes (STEP) and GRavitational lEnsing Accuracy Testing (GREAT) Challenges, measuring galaxy shears is a nontrivial task: various methods introduce different systematic biases which have to be accounted for. We investigate how pixel noise on the image affects the bias on shear estimates from a Maximum-Likelihood forward model-fitting approach using a sum of co-elliptical S\'{e}rsic profiles, in complement to the theoretical approach of an an associated paper. We evaluate the bias using a simple but realistic galaxy model and find that the effects of noise alone can cause biases of order 1-10% on measured shears, which is significant for current and future lensing surveys. We evaluate a simulation-based calibration method to create a bias model as a function of galaxy properties and observing conditions. This model is then used to correct the simulated measurements. We demonstrate that this method can effectively reduce noise bias so that shear measurement reaches the level of accuracy required for estimating cosmic shear in upcoming lensing surveys.