SIMBAD references

We have conducted an optical and infrared imaging in the neighbourhoods of four triplets of quasars. R,z',J and K_simages were obtained with MOSAIC II and ISPI at Cerro Tololo Inter-American Observatory. Accurate relative photometry and astrometry were obtained from these images for subsequent use in deriving photometric redshifts. We analysed the homogeneity and depth of the photometric catalogue by comparing with results coming from the literature. The good agreement shows that our magnitudes are reliable to study large-scale structure reaching limiting magnitudes of R = 24.5,z' = 22.5,J = 20.5 and K_s= 19.0. With this catalogue we can study the neighbourhoods of the triplets of quasars searching for galaxy overdensities such as groups and galaxy clusters.