Total magnitudes of Virgo galaxies. II. An investigation into the m(p) scale of Volume I of Zwicky et al.'s Catalogue of Galaxies and of Clusters of Galaxies

We investigate the photographic-magnitude (in.) scale of Volume I of the Ca talogue of Galaxies and of Clusters of Galaxies for galaxies in the Virgo d irection. It is found that for 11.5 less than or equal to B-t < 14.5, the m (p) values listed correspond very closely (with a scatter of only 0.16 magn itude) to blue magnitudes measured to the <mu>(B) = 24.4 isophote. If m(p) values need to be used as estimates of total blue magnitude the scatter is 0.27 magnitude over the same range in B-t and the mean offset is m(p) - B-t = 0.28 magnitude. However, a serious scale error at the bright end causes both the isophotal and total luminosities of galaxies brighter than Bt simi lar to 11.5 to be severely underestimated. At the faint end there also appe ars to be a significant scale error. This causes galaxy luminosities to be seriously overestimated faintward of B-t similar to 14.5. We demonstrate th at this is a real effect based on a detailed galaxy-by-galaxy study of the catalogue's completeness down to B-t = 17.0. The catalogue is found only to be complete to B-t similar to 14.7 whilst its degree. of incompleteness is found to be relatively constant at the 30% level over the range 14.75 less than or equal to B-t < 15.75. Most of the missing objects are found to be elliptical galaxies and so late-type objects are over-represented at the fa int end.