A radial mass profile analysis of the lensing cluster MS2137-23

We reanalyse the strong lens modeling of the cluster of galaxies MS2137-23 using a new $UBVRIJK$ data set obtained with the ESO VLT. We infer the photometric redshifts of the two main arc systems which are both found to be at $z=1.6\pm 0.1$. After subtraction of the central cD star light in the previous F702/HST imaging we found only one object lying underneath. This object has the expected properties of the fifth image associated to the tangential arc. It lies at the right location, shows the right orientation and has the expected S/N. Using these new constraints we improve the modeling of the central dark matter distribution of the cluster, using an isothermal model with a core, and the NFW-like model. The constraints provided by the fifth image are primary on the center position of the lens, but its position is in better agreement with an isothermal model. The arc positions together with the shear map also better fit the isothermal model. Some generalized-NFW mass profiles are still acceptable, provided its power index is in the range 0.7< \alpha< 1.2. A detailed model including the effect of the stellar mass distribution to the total mass inward does not change our conclusions. Using our new strong+ weak lensing model together with Chandra X-ray data and the cD stellar component we finally discuss intrinsic properties of the gravitational potential. Whereas X-ray and dark matter have a similar orientation and ellipticity at various radius, the cD stellar isophotes are twisted by 13deg. The azimuthal shift we observe between the radial arc position and the predictions of elliptical models correspond to what is expected from a mass distribution twist. This shift may result on a projection effect of the cD and the cluster halos, thus revealing the triaxiality of the mass components.