The morphological segregation of galaxies in clusters .2. The properties of galaxies in the Coma cluster

We have looked for differences in the galaxy properties along the Hubble sequence and for the dependence of these properties on the environment, in an absolute magnitude complete sample of 187 galaxies in the Coma cluster. The morphological type of all galaxies was determined from our own high resolution data. We also compared this sample with other published complete samples of galaxies in the Perseus and Virgo clusters and in the local field. Ellipticals and lenticulars are highly homogeneous in all their internal photometric properties. These galaxies are well described just by their morphological type and luminosity, regardless of the environment. On the other hand, some of the external properties of these galaxies and of their subclasses differ markedly. Then, for early-type galaxies, the environment determines the space density of each type but not the internal properties of the type, which are the same in all environments. Spirals form a heterogeneous class of objects whose photometric properties depend on one extra parameter. As a result, spirals that are blue in the optical also have blue ultraviolet-optical colors, higher mean surface brightness (or smaller radii) for their magnitude, strongly avoid the cluster center and have high velocities relative to the cluster center. The spatial distribution of spirals as a whole class is uniform. For spirals, therefore, the environment does not determine the space density, which is the same in all environments, but strongly affects the internal galaxy properties. The galaxies in Coma, as in Perseus, are segregated primarily with respect to the supercluster main direction, thus providing a new interpretation of the morphology-radius and morphology-density relations. Finally, the NGC 4839 group is richer in early-type galaxies than other regions at the same distance from the cluster center, showing that the morphological segregation could be a useful tool for discriminating fortuitous alignments from real groups.