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

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 $v_{\max }$ 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-$v_{\max }$ 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.

6 pages, 4 figures; minor changes following first referee report (conclusions unchanged)

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• Too dense to go through: The importance of low-mass clusters for satellite quenching
• Improved strong lensing modelling of galaxy clusters using the Fundamental Plane: Detailed mapping of the baryonic and dark matter mass distribution of Abell S1063
• Dianoga SIDM: galaxy cluster self-interacting dark matter simulations
• Pilot-WINGS: An extended MUSE view of the structure of Abell 370
• The galaxy-galaxy strong lensing cross-sections of simulated LCDM galaxy clusters
• Self-Interacting Dark Matter, Core Collapse and the Galaxy-Galaxy Strong Lensing Discrepancy
• The Hateful Eight: Connecting Massive Substructures in Galaxy Clusters like Abell 2744 to their Dynamical Assembly State using the Magneticum Simulations
• Scatter in the satellite galaxy SHMR: fitting functions, scaling relations & physical processes from the IllustrisTNG simulation
• The history and mass content of cluster galaxies in the EAGLE simulation
• Exotic Image Formation in Strong Gravitational Lensing by Clusters of Galaxies -- IV. Elliptical NFW Lenses and Hyperbolic Umbilics
• The Three Hundred: $M_{sub}-V_{circ}$ relation
• Self-Interacting Dark Matter with Mass Segregation: A Unified Explanation of Dwarf Cores and Small-Scale Lenses
• Galaxies in the central regions of simulated galaxy clusters