A COMPARATIVE-STUDY OF MORPHOLOGICAL CLASSIFICATION OF APM GALAXIES

We investigate the consistency of visual morphological classifications of galaxies by comparing classifications for 831 galaxies from six in dependent observers. The galaxies were classified on laser print copy images or on computer screen using scans made with the Automated Plate Measuring (APM) machine. Classifications are compared using the Revis ed Hubble numerical type index T. We find that individual observers ag ree with one another with rms combined dispersions of between 1.3 and 2.3 type units, typically about 1.8 units. The dispersions tend to dec rease slightly with increasing angular diameter and, in some cases, wi th increasing axial ratio (b/a). The agreement between independent obs ervers is reasonably good but the scatter is nonnegligible. In spite o f the scatter, the Revised Hubble T system can be used to train an aut omated galaxy classifier, e.g. an artificial neural network, to handle the large number of galaxy images that are being compiled in the APM and other surveys.