Tracing Structure: Shape and Centroid Deviations in 39 Strong Lensing Clusters as a Test of Cluster Formation Predictions

TL;DR

This study compares the shapes and alignments of different components in strong lensing galaxy clusters to test predictions from $\\Lambda$CDM cosmology, revealing insights into cluster assembly and the relation between dark matter, stars, and gas.

Contribution

It introduces a multi-component analysis of cluster shapes and centroids using diverse observational data to evaluate their alignment and relation to the gravitational potential.

Findings

ICL closely aligned with dark matter halo in position and centroid

ICL and CLM are more elliptical than ICM and BCG

Misalignments are linked to cluster assembly and merger history

Abstract

Strong lensing galaxy clusters provide a unique and powerful way to test simulation-derived structure predictions that follow from $\Lambda$ Cold Dark Matter ($\Lambda$CDM) cosmology. Specifically, the relative alignments of the dark matter (DM) halo, stars, and hot intracluster gas in these clusters offer insights into how well theoretical structure predictions hold. We measure the position angles, ellipticities, and locations/centroids of the brightest cluster galaxy (BCG), the Intracluster Light (ICL), the hot Intracluster Medium (ICM), and the Core Lensing Mass (CLM) for a sample of strong lensing galaxy clusters from the Sloan Giant Arcs Survey (SGAS). We measure the shapes (position angles and ellipticities) and centroids of these distributions using ellipse-fitting methods applied to different datasets: HST WFC3 imaging for the BCG and ICL, Chandra X-ray observations for the ICM, and strong-lensing mass reconstructions for the CLM. Additionally, we incorporate ICM morphological measures to classify the dynamical state of the cluster sample. Using this multi-component approach, we constrain the shape and centroids of these distributions in this sample and evaluate the different observable components in terms of their ability to trace the gravitational potential of their respective clusters. We find that misalignments between cluster components can be explained by astrophysical processes related to cluster assembly, relaxation, and merger histories. We find that the ICL is most closely aligned with its host DM halo, as traced by the CLM distribution, in both position angle and centroid. Additionally, we find that on average the ICL and CLM are more elliptical than the ICM and BCG.