Three-point galaxy-galaxy lensing as a probe of dark matter halo shapes

TL;DR

This paper introduces a new 3-point lensing method to measure dark matter halo shapes, overcoming misalignment issues, and demonstrates its effectiveness with simulations and future survey prospects.

Contribution

It presents a novel 3-point correlation technique to accurately measure dark matter halo ellipticities, immune to galaxy-halo misalignments.

Findings

Systematic errors in ellipticity measurement are below 5%.

Future surveys like LSST can detect halo ellipticities with this method.

The estimator effectively uses all triangle configurations in the 3-point function.

Abstract

We propose a method to measure the ellipticities of dark matter halos using the lens-shear-shear 3-point correlation function. This method is immune to effects of galaxy-halo misalignments that can potentially limit 2-point galaxy-galaxy lensing measurements of halo anisotropy. Using a simple model for the projected mass distributions of dark matter halos, we construct an ellipticity estimator that sums over all possible triangular configurations of the 3-point function. By applying our estimator to halos from N-body simulations, we find that systematic errors in the recovered ellipticity will be at the <5% fractional level. We estimate that future imaging surveys like LSST will have sufficient statistics to detect halo ellipticities using 3-point lensing.