Constraints on MOND from the lensing cluster MS2137-23

The cluster of galaxies MS2137-23 presents the most constrained lensing configuration of gravitational images ever detected in a distant cluster of galaxies. With a set of two arc systems with known redshifts and many other arclets spread between ≈ 30 h−1 kpc and 1 h−1 Mpc, MS2137-27 is well suited to probe its mass profile and to challenge theoretical expectations from CDM scenario with more speculative alternatives, like MOND models. In this note, I describe the recent lensing analysis I carried out on this cluster using together arcs and CHANDRA X-ray data. Even with this unique data set, I cannot reject neither an isothermal model nor an NFW model. The MOND model is not compatible with the observations, unless a significant fraction of the baryonic matter has not been detected by CHANDRA. The need for much more baryons in the MOND model than for the dark matter paradigm implies significant dynamical differences between these models which can be explored at very large radial distance. In particular, MOND lensing signal becomes isotropic beyond 1 h−1 Mpc, in contrast with collisionless DM halos which produce elliptical potentials. This difference can in principle be used to test MOND prescriptions, regardless the exact relation between matter and the gravitational deflection law assumed for MOND.