Estimate of halo ellipticity as a function of radius with flexions

TL;DR

This paper presents a novel method using lensing flexion ratios to measure the radial variation of halo ellipticity, reducing bias and improving accuracy in dark matter halo characterization.

Contribution

The authors introduce a new technique leveraging flexion ratios and a weight function to accurately estimate halo ellipticity as a function of radius, addressing bias issues.

Findings

Method reduces bias in ellipticity estimates

Flexion ratios can trace galaxy cluster centers

Numerical tests confirm accuracy of the approach

Abstract

The cold dark matter theory predicts triaxial dark matter haloes. The radial distribution of halo ellipticity depends on baryonic processes and the nature of dark matter particles (collisionless or collisional). Here we show that we can use lensing flexion ratios to measure the halo ellipticity as a function of radius. We introduce a weight function and study the relationship between the first and second order statistics of flexion ratios, both of which can be used to reduce the bias in the estimate of ellipticity. we perform numerical tests for our method, and demonstrate that it can reduce the bias and determine the halo ellipticity as a function of radius. We also point out that the minimum mean flexion ratio can be used to trace the centres of galaxy clusters.