Structure and formation of superclusters - VI. Morphology-density-luminosity relation of isolated and grouped galaxies.

The morphology and luminosity distributions of isolated and grouped galaxies is studied in three superclusters. The morphology-density relation for grouped galaxies, found by Dressler and by Postman & Geller, is confirmed. The morphology distribution of isolated galaxies depends rather weakly on the degree of isolation. The samples of most isolated galaxies contain no ellipticals and only a few lenticulars. Absolute magnitudes of brightest isolated galaxies are one magnitude fainter than magnitudes of brightest galaxies in groups and clusters. Further support is given to accumulating evidence that observed morphology and luminosity differences between isolated and grouped galaxies are basically intrinsic, due to formation differences.