Shape Profiles and Orientation Bias for Weak and Strong Lensing Cluster Halos

TL;DR

This study investigates the shapes and alignments of galaxy cluster halos from simulations, revealing their prolate nature on small scales, projection biases in concentration estimates, and the alignment of isodensities.

Contribution

It provides a detailed analysis of halo shapes, orientations, and projection effects, including a publicly available catalog of results from the MultiDark MDR1 simulation.

Findings

Halos are extremely prolate on small scales and more spherical on larger scales.

Projection effects can overestimate concentration indices by up to 18%.

Isodensities are well-aligned, but individual halos show axis deviations up to 30 degrees.

Abstract

We study the intrinsic shape and alignment of isodensities of galaxy cluster halos extracted from the MultiDark MDR1 cosmological simulation. We find that the simulated halos, are extremely prolate on small scales, and increasingly spherical on larger ones. Due to this trend, analytical projection along the line of sight produces an overestimate of the concentration index as a decreasing function of radius, which we quantify by using both the intrinsic distribution of 3D concentrations ($c_{200}$) and isodensity shape on weak and strong lensing scales. We find this difference to be $\sim 18\%$ ($\sim 9\%$) for low (medium) mass cluster halos with intrinsically low concentrations ($c_{200}=1-3$), while we find virtually no difference for halos with intrinsically high concentrations. Isodensities are found to be fairly well-aligned throughout the entirety of the radial scale of each halo population. However, major axes of individual halos have been found to deviate by as much as $\sim 30^{\circ}$. We also present a value-added catalog of our analysis results, which we have made publicly available to download.