A demonstration of position angle-only weak lensing shear estimators on the GREAT3 simulations

TL;DR

This paper demonstrates the effectiveness of position angle-only shear estimators on realistic galaxy simulations, addressing biases and achieving performance comparable to established methods in weak lensing analysis.

Contribution

The study applies and evaluates a position angle-only shear estimator on the GREAT3 simulations, incorporating bias correction and multiple measurement techniques.

Findings

Achieved shear estimation with Q~400 for all methods.

Demonstrated bias correction effectiveness in anisotropic PSF conditions.

Performance close to traditional model and moments-based methods.

Abstract

We develop and apply the position angle-only shear estimator of Whittaker et al. (2014) to realistic galaxy images. This is done by demonstrating the method on the simulations of the GREAT3 challenge (Mandelbaum et al. 2014b), which include contributions from anisotropic PSFs. We measure the position angles of the galaxies using three distinct methods - the integrated light method, quadrupole moments of surface brightness, and using model-based ellipticity measurements provided by IM3SHAPE. A weighting scheme is adopted to address biases in the position angle measurements which arise in the presence of an anisotropic PSF. Biases on the shear estimates, due to measurement errors on the position angles and correlations between the measurement errors and the true position angles, are corrected for using simulated galaxy images and an iterative procedure. The properties of the simulations are estimated using the deep field images provided as part of the challenge. A method is developed to match the distributions of galaxy fluxes and half-light radii from the deep fields to the corresponding distributions in the field of interest. We recover angle-only shear estimates with a performance close to current well-established model and moments-based methods for all three angle measurement techniques. The Q-values for all three methods are found to be Q~400. The code is freely available online at http://www.jb.man.ac.uk/~mbrown/angle_only_shear/.