Optical luminosity functions for compact groups of galaxies

We present new results on the optical luminosity function (OLF) of compact groups (CGs) using the data in the catalog assembled by Hickson (1982), the Hickson compact groups (HCGs). We use the Catalog of Paired Galaxies (CPG; Karachentsev 1972) and the Catalog of Isolated Galaxies (CIG; Karachentseva 1973) as control samples. We expected the HCG sample to show an interaction-induced luminosity enhancement at least as large as the one observed in binary samples. We expect this excess because galaxies in CGs are subject to more frequent tidal encounters and mergers. We find only weak evidence for an enhancement among the CG spiral population. We also searched for the expected population of CG merger remnants. If groups merge rapidly and assume the form of field elliptical galaxies we should see the signature of these recent coalescence events in the OLF of field samples like the CIG. We do not find a population of field ellipticals that are luminous enough to be the remnants of merged CGs. It is difficult to see how the CIG selection procedures could have missed this luminous merger population. All the evidence points toward a much longer evolutionary timescale for CGs than current models predict.