Abstract
We present our preliminary results on the study of high luminosity ULIRGs (LFIR > 1012.3 L⊙) in the 1 Jy sample. Deep, high resolution optical R images with a 7 arcmin × 7 arcmin field of view for 2/3 of the whole sample, show that they are generally found in very rich environments, seem to be late-stage merger products (long tidal tails are found in only three systems), and all show multiple nuclei (double nuclei in eleven: two ion{H}{2}, fourLINERs, four Sy2s and one Sy1). The GTC first-light instruments are very well suited for addressing the question of the energy source of ULIRGs and will provide us with a more refined view of the proposed evolutionary sequence.
