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A COMPARATIVE STUDY OF MORPHOLOGICAL CLASSIFICATIONS OF APM GALAXIES

We investigate the consistency of visual morphological classifications of galaxies by comparing classifications for 831 galaxies from six independent observers. The galaxies were classified on laser print copy images or on computer screen produced from scans with the Automated Plate Measuring (APM) machine. Classifications are compared using the Revised Hubble numerical type index T. We find that individual observers agree 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 decrease slightly with increasing angular diameter and, in some cases, with increasing axial ratio $(b/a)$. The agreement between independent observers is reasonably good but the scatter is non-negligible. In spite of the scatter the Revised Hubble T system can be used to train an automated 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.