The Yerkes system of form classification for galaxies was introduced by W. W. Morgan (1958, 1959) at which time he gave classifications for a large number of objects in that system. The primary basis for the new classification was an earlier discovery (Morgan and Mayall 1957) that, for the majority of galaxies, a correlation exists between the integrated spectral type at low dispersion and the degree of central concentration of light in the system. Irregular and spiral galaxies with little or no nuclear concentration have spectra of types A or F, while spirals with relatively large nuclei and giant elliptical galaxies have G and K types. These spectroscopic differences presumably arise from the different stellar populations which dominate the inner regions.
In the Yerkes form classification, therefore, the fundamental parameter the "population group," which is denoted by lower-case letters a through k (as in the stellar spectral sequence). It is determined entirely from the brightness of the nuclear region relative to the body of the galaxy on direct photographs. Two additional parameters make up the Yerkes classification: a "form family" parameter (principally I, S, B, E, and D for irregulars, spirals, barred spirals, ellipticals, and systems with rotational symmetry but no spiral structure, respectively); and an "inclination class" parameter which ranges from 1 (for a circular cross-section) to 7 (for an edge-on system). Further details about the classification system can be found in the papers by Morgan cited above.
A number of photographs were secured during September and October 1971 in order to obtain classifications on the Yerkes system for galaxies in the southern sky, as well as to explore the capabilities of the new University of Toronto 24-inch reflector at the Las Campanas Observatory of the Carnegie Institution of Washington in Chile. The galaxies were photographed on 103a-O and 103a-D plates, which were developed in MWP-2 developer. Because of the fine seeing at Las Campanas and the high optical quality of the telescope, the plates are very suitable for classification. Since the Yerkes system requires relatively short exposures to preserve information about the inner regions of the bright systems observed, exposure times were less than one hour. A number of the most interesting photographs are reproduced in figures 1 - 22.
The classifications for twenty-eight galaxies are listed in Table I. Some of them had previous classifications in the lists of Morgan. Eight of these were adopted as standards in the present classification, as indicated in the Remarks to Table I. A few of the standards were modified slightly after being carefully evaluated. A number of additional comments about individual galaxies are given in the Remarks and Notes to the Table.
We are grateful to the National Research Council of Canada for supporting this research and are indebted to Dr. Horace Babcock and the CARSO staff for their valuable assistance on Las Campanas. Special thanks are due to Warren Magill of the David Dunlap Observatory and to the staff of the University of Toronto Press for their efforts to make high quality reproductions of the original negatives.