A Computational and Observational Study of Peculiar Galaxies in the Coma Cluster

Expected numbers of elliptical galaxies distorted tidally in the Coma cluster are formulated in terms of the various parameters of the cluster, and of cross section of galaxy-galaxy encounters and duration of associated tidal distortions. For the latter two quantities, numerical computations are carried out by simulating elliptical galaxies with hundreds of test particles. Comparisons are made with the number of peculiar galaxies observed in the Coma cluster. The hypothesis that the "missing mass" of the Coma cluster is hidden in the form of invisible galaxies or huge black holes of ordinary galaxy masses is also tested. It is concluded that tidal interaction between the visible galaxies plays only a minor role in the origin of the peculiar galaxies in the Coma cluster. Most of them would be due to their individual non-tidal mechanisms. If invisible galaxies or massive black holes are assumed as cluster members, their encounters with the luminous members increase the frequency of observable tidal distortion, and approximately half of the number of the peculiar galaxies could be explained in terms of tidal interaction. This result is discussed in relation to some special types of the peculiar galaxies in the Coma cluster. Key words: Coma cluster; Missing mass; Peculiar galaxy; Tidal interaction.