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(PostScript file)We have obtained high resolution near-infrared imaging for the Southern ISOPHOT-S ULIRGs to investigate their evolution stage. The majority (68%) of the ULIRGs imaged are double systems and all show distorted morphologies. From the 23 double nuclei systems 17 of them appear at linear separations between 4-14 kpc with a mean separation of 6.5 kpc. Using the separations measured from our new near-infrared imaging as well as from the literature, we have examined whether ULIRGs that are advanced mergers are more AGN-like. We have found no such evidence contrary to what is postulated by the classical evolutionary scenario. No correlation is found between the stage of merger in ULIRGs and their infrared luminosity. In fact we find that systems in the early stages of merging may well output maximum luminosity. We also find that the total mass of interstellar gas, as estimated from the CO (1-0) luminosity, does not decrease with decreasing merger separation. When both an AGN and a starburst occur concurrently in ULIRGs, we find that the starburst dominates the luminosity output. We propose that the available gas reservoir and the individual structure of the interacting galaxies plays a major role in the evolution of the system.
Keywords: galaxies: active -- galaxies: starburst -- infrared: galaxies
Status: Astronomical Journal in press
Address: mailto: dar@mpe.mpg.de
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Last update: 11-Oct-1999 by K.Seidenschwang