Ellipticities of Galaxy Cluster Halos from Halo-Shear-Shear Correlations

TL;DR

This paper presents the first detection of galaxy cluster halo ellipticities using halo-shear-shear correlations, revealing that more massive and high-richness halos tend to be more elliptical, consistent with simulations.

Contribution

Introduces a novel method to measure halo ellipticities without needing major axis determination, using HSSC and shear catalogs from large surveys.

Findings

Average projected ellipticity of dark matter halos is approximately 0.48.

Higher mass halos tend to have larger ellipticities.

High-richness halos show increased ellipticity, indicating dynamical youth.

Abstract

We report the first detection of the halo ellipticities of galaxy clusters by applying the halo-shear-shear correlations (HSSC), without the necessity of major axis determination. We use the Fourier\_Quad shear catalog based on the Hyper Suprime-Cam Survey and the group catalog from the DESI Legacy Surveys for the measurement of group/cluster lensing and HSSC. Our analysis includes the off-centering effects. We obtain the average projected ellipticity of dark matter halos with mass $13.5 < {\rm log} (M_G h/ M_\odot) < 14.5$ within 1.3 virial radius to be $0.48^{+0.12}_{-0.19}$. We divide the sample into two groups based on mass and redshift, and we find that halos with higher mass tend to exhibit increased ellipticity. We also reveal that high-richness halos have larger ellipticities, confirming the physical picture from numerical simulation that high-richiness halos have a dynamical youth and more active mass accretion phase.