Published in PASP 70, 1958.
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A PRELIMINARY CLASSIFICATION OF THE FORMS OF GALAXIES ACCORDING TO
THEIR STELLAR POPULATION
W. W. Morgan
Yerkes
Observatory,
University of Chicago
Abstract. A revised system of classification of the forms of
galaxies is
described. The principal criterion of type is the degree of central
concentration of the light of each galaxy; in this respect the new
system can be considered a modification of that of Hubble.
The basis for the new classification is the spectroscopic work
on composite spectra of galaxies by Morgan and Mayall. The
correlation between form and stellar population found by these
investigators has been utilized to set tip a form classification which
would be indicative of the general kind of stellar population
encountered in the majority of galaxies classified.
A total of 608 galaxies have been classified on the new system
from plates obtained principally by Edwin Hubble in the Mount
Wilson-Palomar collection.
Possible applications of the new classification to problems of
galactic distribution and evolution are outlined. There is a definite
indication of large-scale fluctuations in the average stellar
population characteristics of galaxies within distances corresponding
to redshifts of around 2000 km/sec.
Table of Contents
INTRODUCTION
- REASONS FOR A NEW FORM CLASSIFICATION
- OUTLINE OF THE NEW FORM CLASSIFICATION
- The Terminology for the Fundamental Parameter
- Secondary Parameters: the "Form Family"
- Secondary Parameters: the "Inclination Class"
- Generalities Concerning the Classification
System
- SOME PHOTOGRAPHIC CONSIDERATIONS
- The Amount of Information in a Photographic Image
of a Galaxy
- The Photographic Gradation of the Prints
- A DESCRIPTION OF THE NEW CLASSIFICATION IN TERMS
OF THE STANDARD GALAXIES
- The I Systems (Plates I-V)
- The S Systems (Plates VI-XVI)
- The B Systems (Plates XVII-XIX)
- The D Systems (Plates XX-XXIV)
- Systems With Peculiar or Complex Nuclei
(Plates XXV-XXVII)
- REASONS FOR A NEW CLASSIFICATION. CONCLUSION
- TABLE I
- NOTES TO TABLE I
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