Twist and Turn: Weak Lensing Image Distortions to Second Order

TL;DR

This paper extends weak gravitational lensing analysis to second order by introducing new distortions called twist and turn, and provides estimators and initial constraints using HST survey data.

Contribution

It identifies and characterizes the new distortions twist and turn in weak lensing, including their properties and estimators, advancing the understanding of higher-order lensing effects.

Findings

Mean twist estimator is consistent with zero.

No evidence of systematic effects in twist correlation functions.

First constraints on twist from HST survey data.

Abstract

We account for all the image distortions relevant to weak gravitational lensing to second order. Besides the familiar shear, convergence, rotation and flexions, we find a new image distortion with two distinct descriptions, the twist and the turn. Like rotation, this distortion is not activated gravitationally to first order, but will be activated by systematic effects. We examine the rotational properties of twist and turn, and their effect on images in real and shapelet space. We construct estimators for the new distortion, taking into account the centroid shift which it generates. We then use these estimators to make first constraints on twist using the STAGES HST survey; we find that the mean twist estimator is consistent with zero. We measure correlation functions for our twist estimator on the survey, again finding no evidence of systematic effects.