Gravitational Flexion by Elliptical Dark Matter Haloes

TL;DR

This paper derives equations for gravitational lensing flexion caused by elliptical dark matter haloes, demonstrating that flexion can tightly constrain galaxy halo shapes more effectively than shear in future surveys.

Contribution

It introduces simplified equations for flexion due to elliptical mass distributions, enabling faster computations and improved constraints on galaxy halo ellipticities.

Findings

Flexion constraints are comparable for two types and much tighter than shear.

Flexion can significantly improve measurements of galaxy halo shapes.

Equations are reduced to one-dimensional integrals for computational efficiency.

Abstract

We present equations for the gravitational lensing flexion expected for an elliptical lens mass distribution. These can be reduced to one-dimensional finite integrals, thus saving significant computing time over a full two-dimensional calculation. We estimate constraints on galaxy halo ellipticities for a range of potential future surveys, finding that the constraints from the two different types of flexion are comparable and are up to two orders of magnitude tighter than those from shear. Flexion therefore appears to be a very promising potential tool for constraining the shapes of galaxy haloes from future surveys.