Digital surface photometry of galaxies toward a quantitative classification. III - A mean concentration index as a parameter representing the luminosity distribution

Analysis of the luminosity distribution of 261 galaxies in a homogeneous sample shows that a variety of luminosity profiles can be sequentially characterized by a single parameter related to the central concentration of luminosity, the mean concentration index. A good correlation is found between the index and the morphological type, although the scatter is relatively large. A source of the scatter, variation of the intrinsic surface brightness, is investigated using empirical models. It is suggested that the index when combined with the mean surface brightness, is sensitive to the bulge-to-disk ratio of a galaxy. The mean concentration index versus surface brightness diagram may provide a useful tool to investigate the luminosity structure of a galaxy and to characterize galaxy content of clusters of galaxies out to ∼100 Mpc.