Digital surface photometry of galaxies toward a quantitative classification. IV. Principal component analysis of surface-photometric parameters.

Principal component analysis is applied to five samples composed of galaxies in the Virgo Cluster and the Ursa Major clouds: a standard sample consisting of 201 galaxies, a Virgo sample, an Ursa Major sample, an elliptical sample, and a disk sample. The standard sample includes galaxies of all morphological types. Included in the analysis are four surface-photometric parameters - diameter, magnitude, mean surface brightness, and mean concentration index - derived in the previous papers of this series. The results for these three samples indicate that both elliptical galaxies and disk galaxies lie in the same plane in the space of the four surface-photometric parameters.