Effects of the halo concentration distribution on strong-lensing optical depth and X-ray emission

TL;DR

This study uses simulated galaxy-cluster merger trees to examine how the distribution of halo concentrations affects strong lensing efficiency and X-ray emission, revealing that concentration scatter can significantly increase lensing optical depth.

Contribution

It demonstrates that the scatter in halo concentration distribution influences strong lensing and X-ray properties, with implications for cluster selection and interpretation.

Findings

Concentration scatter increases lensing optical depth by up to 50%.

Less concentrated clusters are often the most efficient lenses and X-ray emitters.

Cluster selection by concentration has minimal impact on lensing cross sections.

Abstract

We use simulated merger trees of galaxy-cluster halos to study the effect of the halo concentration distribution on strong lensing and X-ray emission. Its log-normal shape typically found in simulations favors outliers with high concentration. Since, at fixed mass, more concentrated halos tend to be more efficient lenses, the scatter in the concentration increases the strong-lensing optical depth by $\lesssim50%$. Within cluster samples, mass and concentration have counteracting effects on strong lensing and X-ray emission because the concentration decreases for increasing mass. Selecting clusters by concentration thus has no effect on the lensing cross section. The most efficiently lensing and hottest clusters are typically the \textit{least} concentrated in samples with a broad mass range. Among cluster samples with a narrow mass range, however, the most strongly lensing and X-ray brightest clusters are typically 10% to 25% more concentrated.