MODELING THE CLOVERLEAF - CONTRIBUTION OF A GALAXY CLUSTER AT Z-SIMILAR-TO-1.7

We present a new investigation of the Cloverleaf (z=2.558) based on th e combination of archival HST/WFPC2 data, recent IRAM C0(7-6) maps and wide field CFHT/FOCAM images. The deepest WFPC2 observation (F814W) s hows a significant overdensity of I-814W similar to 23-25 galaxies aro und the Cloverleaf that we interpret as the presence of a cluster of g alaxies along the line of sight. The typical magnitude, red color (R-I similar to 0.9) and small angular size of these galaxies suggest that the cluster is very distant and could be associated with the absorpti on systems observed in the spectra of the quasar spots (either z = 1.4 38, 1.66, 1.87 or 2.07). The Cloverleaf is probably the result of the lensing effects of a system which includes, in addition to a single ga laxy, one of the most distant clusters of galaxies ever detected. With this assumption, we have modelled the lens using the HST/WFPC2 data a nd the IRAM/CO(7-6) map. We have considered two cases: one in which th e mass model is a galaxy and a dark halo at z=1.7, and a second one in which the mass model is the combination of a cluster (centered on the overdensity of galaxies) and an individual galaxy located amid the Cl overleaf, both at z=1.7. The high-resolution IRAM/CO map provides for the first time the orientation and the ellipticity of the CO spots ind uced by the shear component. Velocity - positional effects are detecte d at the 8 sigma level in the CO map. A strong limit can then be put o n the size, shape and location of the CO source around the quasar. The CO source is found to form a disk-or ring-like structure orbiting the central engine at similar to 100 km/s at a radial distance of similar to 100 pc, leading to a central mass of similar to 10(9) M-. possibly in the form of a black hole. The cluster component increases signific antly the convergence of the lens and this pulls down the requirement on the mass of the lensing galaxy by a factor 2. This may help explain the mystery of why the lensing galaxy has not been detected yet. A de ep high resolution infrared image should reveal the nature and locatio n of the lensing galaxy. The presence of an additional lensing cluster along the line of sight to the Cloverleaf strengthens the suspicion t hat many bright quasars are magnified by distant clusters of galaxies at redshifts larger than 1.