G. de Vaucouleurs

THE LUMINOSITY CLASSIFICATION OF GALAXIES AND SOME APPLICATIONS.

Abstract : The Van den Bergh luminosity classification for spiral galaxies was statistically tested for possible systematic effects depending on declination and galactic latitude; no significant correlation can be detected other than a slight excess of high-luminosity systems in low galactic latitudes probably due to selection effects in the Shapley-Ames Catalogue. The calibration of luminosity classes in terms of absolute magnitude was derived from residuals in the velocity-magnitude relation using improved magnitudes in the B system corrected for galactic absorption (mc) and an enlarged list of redshifts (V-o). If L = 1, 2, 3, ..., 9 for DDO classes I, I-II, II, ..., V, then a least-squares fit through the relation, log V-o = const + 0.2(1+mu)m-c-0.1 (1+ lambda)L, gives Mu=0.048=0.047 (m.e.) and lambda=0.029=0.050 (8<m-c<14; n=213 galaxies), i.e., a negligible correction to the previously assumed slope delta-M/deltaL=0.50 and in the mean (over a large area of the sky) a negligible departure from the theoretical slope of the V(m) relation. Van den Berghs data can be used to check Van Albadas suggestion that the anistropy of the velocitymagnitude relation for nearby galaxies is due to systematic variations with direction of the mean absolute magnitude of galaxies having a given type and magnitude. The tests give little support to this hypothesis and systematic departures in the V(m) relations in different parts of the sky remain even when allowance is made for luminosity effects. (Author)