Properties of Very Luminous Galaxies

Recent analysis of the SSRS2 data based on cell-counts and two-pointcorrelation function has shown that very luminous galaxies are much morestrongly clustered than fainter galaxies. In fact, the amplitude of thecorrelation function of very luminous galaxies ($L > L^*$) asymptoticallyapproaches that of $R \ge 0$ clusters. In this paper we investigate theproperties of the most luminous galaxies, with blue absolute magnitude $M_B \le-21$. We find that: 1) the population mix is comparable to that in other rangesof absolute magnitudes; 2) only a small fraction are located in bona fideclusters; 3) the bright galaxy-cluster cross-correlation function issignificantly higher on large scales than that measured for fainter galaxies;4) the correlation length of galaxies brighter than \MB $ \sim -20.0$,expressed as a function of the mean interparticle distance, appears to followthe universal dimensionless correlation function found for clusters and radiogalaxies; 5) a large fraction of the bright galaxies are in interacting pairs,others show evidence for tidal distortions, while some appear to be surroundedby faint satellite galaxies. We conclude that very luminous optical galaxiesdiffer from the normal population of galaxies both in the clustering and otherrespects. We speculate that this population is highly biased tracers of mass,being associated to dark halos with masses more comparable to clusters thantypical loose groups.