Table Of ContentStructure and Evolution of Galaxies
NATO ADVANCED STUDY INSTITUTES SERIES
Proceedings of the Advanced Study Institute Programme, which aims
at the dissemination of advanced knowledge and
the formation of contacts among scientists from different countries
The series is published by an international board of publishers in conjunction
with NATO Scientific Affairs Division
A Life Sciences Plenum Publishing Corporation
B Physics London and New York
C Mathematical and D. Reidel Publishing Company
Physical Sciences Dordrecht and Boston
D Behavioral and Sijthoff International Publishing Company
Social Sciences Leiden
E Applied Sciences Noordhoff International Publishing
Leiden
Series C - Mathematical and Physical Sciences
Volume 21 Structure and Evolution of Galaxies
Structure and Evolution
of Galaxies
Lectures Presented at the NATO Advanced Study Institute
held at the International School of Astrophysics at the
'Ettore M ajorana' Centre for Scientific Culture in Erice (Sicily)
Italy, June 22-July 9, 1974
edited by
G IAN CARLO SETTI
University of B%gna, Laboratorio di Radioastronomia CNR,
Via Irnerio 46, 40126 Bologna, Italy
D. Reidel Publishing Company
Dordrecht-Holland / Boston-U.S.A.
Published in cooperation with NATO Scientific Affairs Division
Library of Congress Cataloging in Publication Data
Main entry under title:
Structure and evolution of galaxies.
(NATO advanced study institutes series: Series C, Mathematical and physical
sciences; v. 21).
"Lectures delivered at the 2nd course of the International School of Astrophysics
at the 'Ettore Majorana' Centre for Scientific Culture in Erice, Sicily, June 22-July 9,
1974."
Includes bibliographical references and index.
1. Galaxies - Congresses. 2. Stars - Congresses. I. Setti, Giaricarlo.
II. Series.
QB857.S86 523.1'12 75-22261
ISBN-13: 978-94-010-1720-6 e-ISBN-13: 978-94-010-1718-3
DOl: 10.1007/978-94-010-1718-3
Published by D. Reidel Publishing Company
P.O. Box 17, Dordrecht, Holland
Sold and distributed in the U.S.A., Canada, and Mexico
by D. Reidel Publishing Company, Inc.
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All Rights Reserved
Copyright © 1975 by D. Reidel Publishing Company, Dordrecht, Holland
No part of the material protected by this copyright notice may be reproduced or utilized
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without permission from the copyright owner
Softcover reprint of the hardcover 1st edition 1975
CONTENTS
FOREWORD vn
S. van den Bergh
GALAXIES INCLUDING GLOBULAR CLUSTERS AND LOCAL GROUP
L. Gratton
STELLAR POPULATIONS 13
L. Woltjer
STELLAR DYNAMICS 45
K. H. Prendergast
MODELS OF GALAXIES 59
E. M. Burbidge
MASS DETERMINATIONS IN SPIRAL GALAXIES; NON-CIRCULAR MOTIONS 71
J. H. Oort
PHENOMENOLOGY OF SPIRAL GALAXIES 85
C. C. Lin
THEORY OF SPIRAL STRUCTURE 119
P. G. Mezger
INTERSTELLAR MATTER 143
F. D. Kahn
DYNAMICS OF INTERSTELLAR MATTER 179
H. Reeves
ATOMS AS MONITORS OF GALACTIC EVOLUTION 197
R. D. Ekers
RADIO CONTINUUM EMISSION FROM GALAXIES 217
VI CONTENTS
S. van den Bergh
DETERMINATION OF THE HUBBLE PARAMETER: AN INTERIM REPORT 247
W. L. W. Sargent
GALAXIES AND THEIR EVOLUTION 261
G. R. Burbidge
GALACTIC NUCLEI AND RADIO SOURCES 275
M. J. Rees
FORMATION OF GALAXIES, RADIO SOURCES AND RELATED PROBLEMS 285
SUBJECT INDEX 325
FOREWORD
This volume contains a series of lectures delivered at the 2nd
course of the International School of Astrophysics at the "Ettore
Majorana" Centre for Scientific Culture in Erice (Sicily) from
June 22 to July 9, 1974.
The course was jointly planned by L. Woltjer and myself and
was fully supported by a grant from the NATO Advanced Study Institute
Programme. It was organized with the aim of providing students and
young researchers with an up to date account of the structure and
evolution of galaxies and was attended by 94 participants from
20 countries.
The study of galaxies is one of the most important areas of
contemporary astrophysics both for its intrinsic interest and
because it is a prerequisite to a quantitative understanding of the
structure of the universe. Recently, a qualitatively new under
standing has become available through both observational andtheore
tical progress. On the observational side, new techniques applied
at the large optical telescopes and, in particular, the impressive
results obtained wi.th the high resolution radio telescopes have made
it possible to obtain a detailed mapping of the structure of galaxies
other than our own. At the same time, new theoretical insights and
the availability of powerful computers to construct models holds
out the hope that a full understanding of the structur.es of galaxies
may be within our reach. The various aspects of this exciting
subject, from the study of our own galaxy to the problem of the
formation of galaxies, have been covered in a series of lectures
totalling 58 hours and 15 topical seminars given by the participants.
I wish to express my gratitude to the Scientific Affairs Division
of the North Atlantic Treaty Organization for the generous support
given to the course and to Prof. A. Zichichi for providing the
facilities of the "E. Majorana" Centre. I am also deeply indebted
to Dr. G. Zamorani for his invaluable assistance in the editing of
this volume; to Mr. L. Baldeschi for helping with the organization
of the meeting and for preparing a number of the diagrams contained
in this volume; to Mrs. B. Mandel for the patient typing of much of
this material; to Mrs. P. Zanlungo-Greiger and Miss P. Savalli for
secretarial assistance in Erice; and to Mr. R. Primavera for the
photographic reproduction of many of the figures.
VIII FOREWORD
A special thanks is, of course, due to all of the lecturers
and participants who have contributed so much to the success of the
course and have provided the manuscripts for this volume.
Finally, I want to express my sincere gratitude to Prof. L.
Woltjer, with whom it has been a pleasure to work.
Giancarlo Setti
University of Bologna
Laboratorio di Radioastronomia CNR
Via Irnerio 46
40126 Bologna, Italy
GALAXIES INCLUDING GLOBULAR CLUSTERS AND LOCAL GROUP
S. van den Bergh
David Dunlap Observatory, University of Toronto
Richmond Hill, Ontario, Canada
1. STELLAR POPULATIONS IN THE GALAXY
According to Baade (1944) the stellar population in the central
bulge of M3l resolves at the same magnitude level as do the glob
ular clusters associated with that galaxy. This observation led
Baade to conclude that the nuclear bulge of the Andromeda Nebula
consists of globular cluster-like stars. He immediately realized
that this idea could be tested by studying the stellar content
of the nuclear bulge of our own galactic system. In particular it
should be possible to observe the RR Lyrae variables in the nuclear
bulge of the Galaxy which would be associated with such a globular
cluster-like population. Baade (1951) therefore proceeded to search
for such cluster-like variables in a low-absorpt~on window centered
on the globular cluster NGC6522 at ~=lo, b=-4°. The expectation
that the nuclear bulge should contain large numbers of RR Lyrae
stars was fully confirmed by Baade (1951) who found more than 100
such variables in the field surrounding NGC6522. At first sight this
observation appeared to give strong support to the view that the
nuclear bulge of the galaxy consists of a globular cluster-like
population.
The first doubts about this population picture, in which ellip
tical galaxies and the central bulges of spiral nebulae consist of
globular cluster-like stars, arose in 1957. Morgan and Mayall (1957)
were able to show that the integrated spectrum of the nuclear region
of M3l is dominated by cyanogen giants. This observation shows that
the dominant contribution to the blue-green region of the spectrum
is provided by strong-lined (i.e. not metal-poor) stars. Subsequently
Nassau and Blanco(1958) were able to show that the RR Lyrae stars
in the field surrounding NGC6522 were outnumbered two to one by
G. Setti red.), Stmcture and Evolution of Galaxies, 1-11. All Rights Reserved.
Copyright © 1975 by D. Reidel Publishing Company, Dordrecht-Holland.
2 s. VAN DEN BERGH
M-type giants. Since M giants do not occur in halo-type globular
clusters it follows that the dominant stellar population in the
nuclear bulge of the galaxy cannot be pure Population II. This
conclusion was strongly confirmed by Morgan {1959) who was able to
show that the integrated spectrum of the nuclear bulge is dominated
by strong-lined cyanogen giants. This conclusion is confirmed by
observations of the colour-magnitude diagram of the nuclear bulge
at b=-4° by van den Bergh (1971). These observations show that the
dominant stellar population at [Z[=0.6 kpc resembles that in the
old metal-rich cluster NGC188. Metal-poor halo stars account for
at most a few percent of all giant stars. UBV photometry of sky-
free star patches in the nuclear bulge also shows that most of the
brightest main sequence stars in the nuclear bulge must be metal-rich.
Within the nuclear bulge the fraction of metal-poor stars is observed
to increase with increasing distance from the galactic plane. At
[ZI=1.2 kpc van den Bergh (1974) finds a significantly larger frac
tion of Population II giants than are observed at IZ[=0.6 kpc.
The model which emerges from these studies is that the dominant
stellar population in the nuclear bulge of the Galaxy consists of
old metal-rich stars similar to those in the old open cluster
NGC188 and that it contains only a sprinkling of true globular
cluster stars.
The colour-magnitude diagram of stars near the Sun shows that
these objects constitute a mixed population that contains young
spiral arm stars, large numbers of old disk stars and a sprinkling
of metal-poor stars. The radial variation in the relative importance
of old and young stellar populations in the Galaxy is dramatically
shown in spectra published by Morgan and Osterbrock (1969). These
show that the spectrum of the i~tegrated light of the nuclear bulge
of the Galaxy observed through the transparent window near NGC6522
has a spectral type near KO with the metallic line indicator near
A4390 being strong. This indicates that most of the light is contrib
uted by metal-rich stars. A spectrum obtained from a partially
obscured region about 20 from NGC6522 shmvs a strenghtening of Hy
and Ho yielding an overall integrated spectral type near F8 for the
galactic disk. This observation shows that the integrated spectral
type of the galaxy exhibits a radial variation in the same sense as
that which is observed in the Andromeda Nebula.
The first evidence for a possible metallicity gradient within
th~ galactic disk was provided by van den Bergh (1958) who showed
that Cepheids with periods in the range two to four days are predom
inantly located in the anti-centre direction whereas Cepheids with
periods of seven to nine days mainly occur in the direction towards
the galactic centre. This conclusion has recently been strenghtened
by Hartwick (1970) who finds that the ratio of the number of red to
blue supergiants increases with increasing distance from the galactic
centre as it does in M33 (Walker 1964). Finally Janes and McClure
(1972) find that K giants with unusually strong cyanogen absorption
probably originated in regions interior to the Sun. These observa
tions of a possible abundance gradient among the stars in the
