The relationship between substructure in 2D X-ray surface brightness images and weak lensing mass maps of galaxy clusters: A simulation study

TL;DR

This study uses high-resolution simulations to compare 2D X-ray and weak lensing maps of galaxy clusters, revealing the potential and limitations of current observational techniques in identifying substructures.

Contribution

Introduces a novel unsharp-masking method for identifying substructures in simulated galaxy cluster maps and analyzes the correlation between substructure mass and area.

Findings

Almost all dark matter subhaloes with M>10^12 h^-1 M_sun are identified at full resolution.

Approximately one third of galaxy-sized substructures lack X-ray counterparts.

Mass-area correlation persists even when maps are degraded to observational resolution.

Abstract

In this paper, we undertake a study to determine what insight can be reliably gleaned from the comparison of the X-ray and the weak lensing mass maps of galaxy clusters. We do this by investigating the 2D substructure within three high-resolution cosmological simulations of galaxy clusters. Our main results focus on non-radiative gas dynamics, but we also consider the effects of radiative cooling at high redshift. For our analysis, we use a novel approach, based on unsharp-masking, to identify substructures in 2D surface mass density and X-ray surface brightness maps. At full resolution (~ 15 h^-1 kpc), this technique is capable of identifying almost all self-bound dark matter subhaloes with M>10^12 h^-1 M_sun. We also report a correlation between the mass of a subhalo and the area of its corresponding 2D detection; such a correlation, once calibrated, could provide a useful estimator for substructure mass. Comparing our 2D mass and X-ray substructures, we find a surprising number of cases where the matching fails: around one third of galaxy-sized substructures have no X-ray counterpart. Some interesting cases are also found at larger masses, in particular the cores of merging clusters where the situation can be complex. Finally, we degrade our mass maps to what is currently achievable with weak-lensing observations (~100 h^-1 kpc at z=0.2). While the completeness mass limit increases by around an order of magnitude, a mass-area correlation remains. Our paper clearly demonstrates that the next generation of lensing surveys should start to reveal a wealth of information on cluster substructure. (Abridged)