The galaxy-galaxy strong lensing cross-sections of simulated LCDM galaxy clusters

TL;DR

This study uses high-resolution hydrodynamical simulations to evaluate galaxy-galaxy strong lensing probabilities in galaxy clusters, finding current models align with observations and do not challenge LCDM cosmology.

Contribution

It demonstrates the importance of simulation resolution and galaxy formation models in accurately predicting GGSL probabilities in LCDM clusters.

Findings

Numerically converged GGSL probabilities require higher resolution simulations.

Different galaxy formation models yield varying substructure densities affecting GGSL.

Observed GGSL rates are consistent with LCDM predictions.

Abstract

We investigate a recent claim that observed galaxy clusters produce an order of magnitude more galaxy-galaxy strong lensing (GGSL) than simulated clusters in a LCDM cosmology. We take galaxy clusters from the C-EAGLE hydrodynamical simulations and calculate the expected amount of GGSL for sources placed behind the clusters at different redshifts. The probability of a source lensed by one of the most massive C-EAGLE clusters being multiply imaged by an individual cluster member is in good agreement with that inferred for observed clusters. We show that numerically converged results for the GGSL probability require higher resolution simulations than had been used previously. On top of this, different galaxy formation models predict cluster substructures with different central densities, such that the GGSL probabilities in LCDM cannot yet be robustly predicted. Overall, we find that galaxy-galaxy strong lensing within clusters is not currently in tension with the LCDM cosmological model.