Weak gravitational lensing with DEIMOS

TL;DR

This paper presents a new, mathematically exact method for weak gravitational lensing measurements that deconvolves galaxy brightness moments from the PSF without shape assumptions, demonstrating high accuracy and competitive performance.

Contribution

The paper introduces a novel deconvolution technique for weak lensing that uses iterative Gaussian weighting and higher-order moments, improving shear estimation accuracy.

Findings

Accurately estimates shear without shape assumptions.

Performs well on GREAT08 challenge data.

Offers a complete C++ implementation.

Abstract

We introduce a novel method for weak-lensing measurements, which is based on a mathematically exact deconvolution of the moments of the apparent brightness distribution of galaxies from the telescope's PSF. No assumptions on the shape of the galaxy or the PSF are made. The (de)convolution equations are exact for unweighted moments only, while in practice a compact weight function needs to be applied to the noisy images to ensure that the moment measurement yields significant results. We employ a Gaussian weight function, whose centroid and ellipticity are iteratively adjusted to match the corresponding quantities of the source. The change of the moments caused by the application of the weight function can then be corrected by considering higher-order weighted moments of the same source. Because of the form of the deconvolution equations, even an incomplete weighting correction leads to an excellent shear estimation if galaxies and PSF are measured with a weight function of identical size. We demonstrate the accuracy and capabilities of this new method in the context of weak gravitational lensing measurements with a set of specialized tests and show its competitive performance on the GREAT08 challenge data. A complete C++ implementation of the method can be requested from the authors.