A persistent excess of galaxy-galaxy strong lensing observed in galaxy clusters

Massimo Meneghetti, Weiguang Cui, Elena Rasia, Gustavo Yepes, Ana Acebron, Giuseppe Angora, Pietro Bergamini, Stefano Borgani, Francesco Calura, Giulia Despali, Carlo Giocoli, Giovanni Granata, Claudio Grillo, Alexander Knebe, Andrea V. Macciò, Amata Mercurio, Lauro Moscardini, Priyamvada Natarajan, Antonio Ragagnin, Piero RosatiEros Vanzella

Research output: Contribution to journalArticlepeer-review


Context. Previous studies have revealed that the estimated probability of galaxy-galaxy strong lensing in observed galaxy clusters exceeds the expectations from the Λ cold dark matter cosmological model by one order of magnitude. Aims. We aim to understand the origin of this excess by analyzing a larger set of simulated galaxy clusters, and investigating how the theoretical expectations vary under different adopted prescriptions and numerical implementations of star formation and feedback in simulations. Methods. We performed a ray-tracing analysis of 324 galaxy clusters from the THREE HUNDRED project, comparing the GADGET-X and GIZMO-SIMBA runs. These simulations, which start from the same initial conditions, were performed with different implementations of hydrodynamics and galaxy formation models tailored to match different observational properties of the intracluster medium and cluster galaxies. Results. We find that galaxies in the GIZMO-SIMBA simulations develop denser stellar cores than their GADGET-X counterparts. Consequently, their probability for galaxy-galaxy strong lensing is higher by a factor of ∼ 3. This increment is still insufficient to fill the gap with observations as a discrepancy by a factor ∼ 4 still persists. In addition, we find that several simulated galaxies have Einstein radii that are too large compared to observations. Conclusions. We conclude that a persistent excess of galaxy-galaxy strong lensing exists in observed galaxy clusters. The origin of this discrepancy with theoretical predictions is still unexplained in the framework of the cosmological hydrodynamical simulations. This might signal a hitherto unknown issue with either the simulation methods or our assumptions regarding the standard cosmological model.

Original languageEnglish (US)
Article numberL2
JournalAstronomy and Astrophysics
StatePublished - Oct 1 2023


  • Dark matter
  • Galaxies: clusters: general
  • Gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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