ABSTRACT
Various concentrations of galaxies are observed, from poor groups to rich clusters. The study of clusters of galaxies is important both for understanding their intrinsic natures as fundamental systems where galaxies are formed and evolve, and for investigating the large-scale structure of the universe. The cD galaxies which play an important role in the classifications are defined as extraordinarily large D galaxies. The luminosity function, which is the number of member galaxies as a function of magnitude or luminosity, is a useful tool for investigation of the photometric properties of clusters of galaxies. The close coincidence of the distance between the two groupings greatly contributes to reducing the uncertainty in distance inherent to extragalactic works dealing with a large sample. In order to study the basic physics behind the structure and formation mechanism of galaxies, it is essential to know how many independent parameters are present.
