A new strong-lensing model for the massive galaxy cluster PLCKG287.0+32.9.

Galaxy clusters are an essential tool to constrain cosmological models and the study of their mass distribution can be used to test the predictions of the currently favoured $\Lambda$-CDM model. Cosmological simulations, in fact, produce accurate predictions and any significant deviations from the theoretical expectations would imply that the dynamical history of the hierarchical formation of clusters does not proceed according to the $\Lambda$-CDM paradigm, for example, because of a different nature of Dark Matter. In this context, using newly obtained VLT/MUSE spectroscopic data, we present a new strong lensing model of the galaxy cluster PLCKG287.0+32.9, a powerful gravitational lens at $z=0.38$ for which previous works, based solely on photometry, found a very large Einstein radius $\theta_e$ > $40''$. The study of this cluster could help to shed some light on the tension between the predictions of $\Lambda$-CDM model and observational evidence found in other powerful lenses: being at the highly non-linear tail of the probability distribution of Einstein radii, an accurate lensing model can actually make the difference between a mild outlier for $\Lambda$-CDM and a clear challenge.