1998A&A...339L..65K

We present new elements in the identification of the Cloverleaf lens-system based on recent NICMOS-2/F160W observations. After a careful PSF subtraction of the 4 images of the quasar, the residual H_F160W image reveals the presence of a faint object (H∼20.5) amid the 4 quasars. This object corresponds to a single galaxy that we identify as the primary lens of the lens-system. From the R, I and H photometry of the galaxies surrounding the Cloverleaf we also derive a photometric redshift. We find that most of them are consistent with belonging to a galaxy cluster/group with mean redshift <z≥0.9±0.1: they are likely to be the other component in the lens-system that provides the additional ``external" shear. Furthermore, we detect 2 very red objects (I-H∼4): the faintest one has no observed optical (R_F702W and I_F814W) counterpart, and the brightest has a predicted redshift z∼2, and may be identified with one of the Cloverleaf absorbers. This gravitational-lens system constitutes an excellent target for imaging/spectroscopy with the new generation of 8m ground-based telescopes.