Strongly lensed cluster substructures are not in tension with $\Lambda$CDM

TL;DR

This study compares observed galaxy cluster substructures with simulations and finds good agreement, indicating no tension with the DM model and highlighting the importance of baryonic physics in simulations.

Contribution

It demonstrates that DM simulations with baryons accurately reproduce observed subhalo properties, challenging previous claims of discrepancies.

Findings

Simulated subhalo mass distribution matches observations.

Mass-max relation agrees with observed data.

Results suggest no tension between DM and observed cluster substructures.

Abstract

Strong gravitational lensing observations can test structure formation models by constraining the masses and concentrations of subhaloes in massive galaxy clusters. Recent work has concluded that cluster subhaloes are more abundant and/or concentrated than predicted by $\Lambda$CDM simulations; this finding has been interpreted as arising from unidentified issues with simulations or an incorrect understanding of the nature of dark matter. We test these hypotheses by comparing observed subhalo masses and maximum circular velocities $v_\mathrm{max}$ to predictions from the high resolution Hydrangea galaxy cluster simulation suite, which is based on the successful EAGLE galaxy formation model. The simulated subhalo mass distribution and mass-$v_\mathrm{max}$ relation agrees well with observations, due to the presence of baryons during tidal stripping. Similar agreement is found for the lower-resolution Illustris-TNG300 simulation. In combination, our results suggest that the abundance and concentration of cluster substructures are not in tension with $\Lambda$CDM, but may provide useful constraints for the refinement of baryon physics models in simulations.