Shear Measurement with Poorly Resolved Images

TL;DR

This paper investigates the impact of poor seeing conditions on weak lensing shear measurements, demonstrating that accurate shear estimators can be obtained even with relatively low-resolution images.

Contribution

It shows that shear measurements remain accurate with seeing sizes around 1.5 arcsec, challenging the assumption that excellent seeing is necessary for weak lensing.

Findings

No correlation between systematic shear error and image resolution.

Shear estimators remain accurate with poorer seeing conditions.

Fourier Quad pipeline effectively measures shear in suboptimal images.

Abstract

Weak lensing studies typically require excellent seeing conditions for the purpose of maximizing the number density of well-resolved galaxy images. It is interesting to ask to what extent the seeing size limits the usefulness of the astronomical images in weak lensing. In this work, we study this issue with the data of the DECam Legacy Survey (DECaLS), which is a part of the target selection program for the Dark Energy Spectroscopic Instrument (DESI). Using the Fourier Quad shear measurement pipeline, we demonstrate that images with relatively poor seeing conditions (around 1.5 arcsec) can still yield accurate shear estimators. We do not find any correlation between systematic shear error and the image resolution.