IDENTIFICATION OF A HIGH-REDSHIFT CLUSTER IN THE FIELD OF Q2345+007 THROUGH DEEP BRIJK PHOTOMETRY

This paper describes new results on the identification of the complex gravitational lens responsible for the double quasar Q 2345+007. A gra vitational shear field was detected recently about 45 '' away from the QSO, centered on an excess of faint blue galaxies. The redshift distr ibution is still unknown, so the mass and the photometric properties o f the deflector are still a matter of debate. We present deep photomet ric data obtained in the near-IR (J and K'), which are used together w ith preexisting optical BRI photometry to build spectral energy distri butions for all the objects of the field, and to derive a photometric redshift estimate by comparison with synthetic spectrophotometric data . We propose a statistical method to analyse the redshift distribution , based on the cumulative histogram of the redshift ranges allowed for the different objects. An excess of galaxies at a redshift of z simil ar or equal to 0.75 is clearly detected in the field of Q 2345+007, wi th a 2D distribution showing a maximum located at the center of the we ak shear field. Besides, the redshift inferred for this cluster is als o compatible with that found for an absorption system in the spectrum of the B component of the quasar. We interpret this overdensity of obj ects as a distant cluster of galaxies responsible for the gravitationa l shear field. Two other redshift concentrations are studied: z = 0.28 which corresponds to the spectroscopic redshift of three galaxies but for which no strong excess of objects is identified, and z similar or equal to 1.2, where an excess of galaxies is also detected, but with a rather smooth 2D distribution over our field of view. We also discus s the existence of other possible excesses of galaxies at redshift pla nes compatible with the absorption systems detected in the spectra of the QSOs. Most cluster-member candidates at z similar or equal to 0.75 are undergoing a star-formation process or are burst systems where th e star formation stopped between 1 and 3 Gyr ago.