Halo cluster shapes: Insights from simulated galaxies and ICL with prospects for weak lensing applications

TL;DR

This study uses hydrodynamical simulations to analyze galaxy cluster shapes and alignments, assessing how luminous tracers like galaxy members and intra-cluster light can inform weak lensing measurements and cluster shape estimations.

Contribution

It provides new insights into the alignment and shape of galaxy cluster components, evaluating the effectiveness of luminous tracers for weak lensing and shape constraints.

Findings

Galaxy members and ICL are less spherical than DM but well aligned with the cluster's major axis.

Galaxies in more concentrated subhalos are more elongated and better aligned with DM.

Positions of galaxy members can reliably trace cluster surface density orientation.

Abstract

We present a detailed study of the shapes and alignments of different galaxy cluster components using hydrodynamical simulations. We compute shape parameters from the Dark Matter (DM) distribution, the galaxy members and the intra-cluster light (ICL). We assess how well the DM cluster shape can be constrained by means of the identified galaxy member positions and the ICL. Further, we address the dilution factor introduced when estimating the cluster elongation using weak-lensing stacking techniques, which arises due to the misalignment between the total surface mass distribution and the distribution of luminous tracers. The dilution is computed considering the alignment between the DM and the Brightest Cluster Galaxy, the galaxy members and the ICL. Our study shows that distributions of galaxy members and ICL are less spherical than the DM component, although both are well aligned with the semi-major axis of the later. We find that the distribution of galaxy members hosted in more concentrated subhalos is more elongated than the distribution of the DM. Moreover, these galaxies are better aligned with the dark matter component compared to the distribution of galaxies hosted in less concentrated subhalos. We conclude that the positions of galaxy members can be used as suitable tracers to estimate the cluster surface density orientation, even when a low number of members is considered. Our results provide useful information for interpreting the constraints on the shapes of galaxy clusters in observational studies.