Core Mass Estimates in Strong Lensing Galaxy Clusters Using a Single-Halo Lens Model

TL;DR

This paper evaluates a simplified single-halo lens model for estimating galaxy cluster core masses from strong lensing data, demonstrating its accuracy and limitations using simulated images.

Contribution

It introduces and tests the Single-Halo Model (SHM) as an efficient, automated method for estimating cluster core masses from lensing constraints, with quantified accuracy.

Findings

Projected core mass has ~8.5% scatter and 0.9% bias compared to true mass.

Excluding models that fail visual inspection reduces scatter to ~3.9%.

Lensing geometry affects model success, especially for giant arc configurations.

Abstract

The core mass of galaxy clusters is an important probe of structure formation. Here, we evaluate the use of a Single-Halo model (SHM) as an efficient method to estimate the strong lensing cluster core mass, testing it with ray-traced images from the `Outer Rim' simulation. Unlike detailed lens models, the SHM represents the cluster mass distribution with a single halo and can be automatically generated from the measured lensing constraints. We find that the projected core mass estimated with this method, M$_{\rm SHM}$, has a scatter of $8.52\%$ and a bias of $0.90\%$ compared to the "true" mass within the same aperture. Our analysis shows no systematic correlation between the scatter or bias and the lens-source system properties. The bias and scatter can be reduced to $3.26\%$ and $0.34\%$, respectively, by excluding models that fail a visual inspection test. We find that the SHM success depends on the lensing geometry, with single giant arc configurations accounting for most of the failed cases due to their limiting constraining power. When excluding such cases, we measure a scatter and bias of $3.88\%$ and $0.84\%$, respectively. Finally, we find that when the source redshift is unknown, the model-predicted redshifts are overestimated, and the M$_{\rm SHM}$ is underestimated by a few percent, highlighting the importance of securing spectroscopic redshifts of background sources. Our analysis provides a quantitative characterization of M$_{\rm SHM}$, enabling its efficient use as a tool to estimate the strong lensing cluster core masses in the large samples, expected from current and future surveys.