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| © CAMBRIDGE UNIVERSITY PRESS 1998 |
Galaxies are like people. The better you get to know them the more peculiar they often seem to become. Each individual galaxy may be thought of as representing a deviation from some underlying ideal type. ``Classical morphology is useful because it succeeds to some extent in distinguishing galaxies which are physically different'' (Kormendy 1982, p. 125). It is the task of a galaxy morphologist (1) to recognize the archetype to which a galaxy belongs, and (2) to organize these archetypes of galaxies into a simple scheme that might eventually be interpreted in terms of galactic evolution. This review is mainly devoted to the morphology and classification of normal galaxies, which may be regarded as objects that are in the ``ground state'' (Ozernoy 1974). Galaxies in excited states, such as quasars and Seyfert galaxies, will not be discussed in detail. Furthermore no mention will be made of purely descriptive classification systems such as those of Wolf (1908) and of Vorontsov-Velyaminov & Krasnogorskaja (1962). For a more detailed discussion of such systems the reader is referred to Sandage (1975). An Atlas of Peculiar Galaxies, that appear to fall outside the range of morphological types that are usually encountered among galaxies, has been published by Arp (1966). The vast majority of objects pictured in Arp's atlas appear peculiar because they are interacting (or have recently interacted) with their companions. However, some objects in Arp's catalog are dwarfs that are not peculiar at all (e.g. Atlas Nos. 2, 3, 4 and 5). Such dwarfs were probably included only because late-type dwarf galaxies generally look patchier, and hence more chaotic, than more luminous galaxies. Furthermore such dwarfs are rare (and therefore unfamiliar to many of us) in galaxy samples that have been selected by apparent magnitude.
For an excellent introduction to the beauty and variety of galaxy morphology the reader is referred to The Color Atlas of Galaxies (Wray 1988) which shows how dust, old red stars, and young blue stars, are distributed in different types of galaxies.