A simple fitting method (gfit) for galaxy shape measurement in weak lensing surveys

TL;DR

The paper introduces gfit, a simple forward deconvolution method for galaxy shape measurement in weak lensing surveys, achieving low bias and efficient performance on simulated data.

Contribution

It presents a novel, simple fitting approach using a single elliptical Sersic profile to measure galaxy shapes with minimal systematic errors.

Findings

gfit achieved the lowest additive bias among tested methods

gfit obtained the second lowest multiplicative bias

gfit demonstrated competitive performance with low computational cost

Abstract

It is anticipated that the large sky areas covered by planned wide-field weak lensing surveys will reduce statistical errors to such an extent that systematic errors will instead become the dominant source of uncertainty. It is therefore crucial to devise numerical methods to measure galaxy shapes with the least possible systematic errors. We present a simple "forward deconvolution" method, gfit, to measure galaxy shapes given telescope and atmospheric smearings, in the presence of noise. The method consists in fitting a single 2D elliptical S\'ersic profile to the data, convolved with the point spread function. We applied gfit to the data proposed in the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Galaxy Challenge. In spite of its simplicity, gfit obtained the lowest additive bias {($\sqrt{\mathcal{A}}=0.057\times10^{-4}$)} on the shear power spectrum among twelve different methods and the second lowest multiplicative bias {($\mathcal{M}/2=0.583\times10^{-2}$)}. It remains that gfit is a fitting method and is therefore affected by noise bias. However, the simplicity of the underlying galaxy model combined with the use of an efficient customized minimization algorithm allow very competitive performances, at least on the GREAT10 data, for a relatively low computing time.