Weak lensing analysis of MS 1008-1224 with the VLT

We present a gravitational lensing analysis of the cluster of galaxies MS 1008-1224 (z = 0.31), based on very deep observations obtained using the VLT with FORS1 and ISAAC during the science verification phase. Two different mass reconstruction algorithms were applied to the B-, V-, R- and I-band data to obtain similar projected mass distributions in all the bands. The FORS1 (BVRI) and ISAAC (JK) data were combined to determine the photometric redshift distribution of galaxies within the ISAAC field and to estimate the mass. We inferred from weak shear a minimum mass of 2.3 x 10(14) h(-1) M-circle dot on large scales (within similar to700 h(-1) kpc, diameter) which agrees well with the X-ray mass mass estimate. The Mass-to-light ratios are also in excellent agreement. The observed mass profile is consistent with Pseudo-Isothermal Sphere models as well as a Navarro, Frenk and White model. In the inner regions the lensing mass is about twice as high as the X-ray mass which supports the long-held view that complex physical processes occuring in the innermost parts of lensing-clusters are mainly responsible for the X-ray-lensing mass discrepancy. We found that the central part of the cluster comprises two mass peaks whose center of mass is located 10-20 arcsec north of the cD galaxy. A similar offset between the cD and the peak of the X-ray distribution has been reported before. The optical, X-ray and the mass distributions show that MS 1008-1224 is composed of several subsystems which are probably undergoing a merger. It is likely that the gas is not in equilibrium in the innermost regions which vitiates the X-ray mass estimate there. We discovered that MS 1008-1224 shows a remarkable case of cluster-cluster lensing. The photometric redshifts show an excess of galaxies located 30 arcsec south-west of the cD galaxy at a redshift of similar to0.9. This distant cluster is therefore also lensed by MS 1008-1224, which, if confirmed with spectroscopic data, would make this the first known case of magnification of a distant cluster by another one.