EVOLUTION OF LUMINOUS IRAS SOURCES - CCD IMAGING

We present optical imaging of a sample of 64 luminous IRAS galaxies which cover a wide range of IRAS spectra and luminosity and also include a range of optical types. The objects are almost all in current or recent tidal interaction. We discuss the connections between the strength and age of the interaction, the IR spectrum and luminosity, and the optical colors, and other properties of the galaxies. The principal result is that the powerful IR sources with steep IR spectra are stronger and dynamically younger interacting systems, while the flat IR spectrum objects are older. We discuss star formation, dust obscuration, and the timescales for nuclear activity compared with IR and tidal events. We describe a self-consistent evolution scenario connecting the luminous IR sources. We suggest that there are two principal evolution paths in IR-luminous galaxies, mainly depending on whether a nuclear broad emission-line region is formed. The suggested evolution connects one type of Sy 2 galaxy with LINERs, and another type of Sy 2 with Sy 1 and QSO galaxies.