ULIRGs: Origin and Evolution

We present our preliminary results on the study of the high luminosity ULIRGs (log(LFIR) > 12.3) in the 1Jy sample. Deep, high resolution optical R images with 7 arcmin x 7 arcmin field of view for 2/3 of the whole sample, show that they are generally found in very rich environments, they seem to be late stage merger products (long tidal tails are found in only 3 systems) and all of them show multiple nuclei (double nuclei in 11: 2HII, 4 LINERs, 4 Sy2 and 1 Sy1). GTC first light instruments are very well suited for addressing the question of the energy source of ULIRGs, together with a more refined view of the proposed evolutionary sequence.