Starbursts Triggers, Nature, and Evolution: Les Houches School, September 17–27, 1996

264 Pages·1998·8.41 MB·English

by  R. Kennicutt (auth.)

STARBURSTS
TRIGGERS, NATURE,
AND EVOLUTION
Les Bouches School, September 17-27, 1996
Editors
Bruno GUIDERDONI
Ajit KEMBHAV I
EDP Sciences
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Springer-Verlag
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Centre de Physique des Houches
Books already publisbed in tbis series
1 Porous Silicon Science and Technology
6 Catalysis by Metals
J.-C. VIAL and J. DERRIEN, Eds. 1995
A. J. RENOUPREZ
2 Nonlinear Excitations in Biomolecules and H. JOBIC, Eds. 1997
M. PEYRARD, Ed. 1995
3 Beyond Quasicrystals 7 Scale Invariance and Beyond
F. AXEL and D. GRATIAS, Eds. 1995 B. DUBRULLE, F. GRANER
4 Quantum Mechanical Simulation Methods and D. SORNETTE, Eds. 1997
for Studying Biologica! Systems 8 New Non-Perturbative Methods and
D. BICOUT and M. FIELD, Eds. 1996
Quantization on the Light Cone
5 New Tools in Turbulence Modelling P. GRANGE, A. NEVEU, H.C. PAUL!,
O. METAIS and J. FERZIGER, Eds. 1997 S. PINSKY and E. WERNER, Eds 1998
Book series coordinated by Michele LEDUC
Editors of "Starbursts: Triggers, Nature, and Evolution" (N° 9)
Bruno Guiderdoni (Institut d' Astrophysique de Paris, CNRS, France)
Ajit Kembhavi (lnter-University Centre for Astronomy and Astrophysics, Pune,
India)
ISBN 978-2-86883-334-1 ISBN 978-3-662-29742-1 (eBook)
DOI 10.1007/978-3-662-29742-1
This work is subject to copyright. Ali rights are reserved, whether the whole or part of the material is
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laws ofMarch Il, 1957 and September 9, 1965, respectively. Violations fali under the prosecution act of
the French and German Copyright Laws.
© Springer-Verlag Berlin Heidelberg 1998
Originally published by Springer-Verlag Berlin Heidelberg New York in 1998
Softcover reprint ofthe hardcover 1st edition 1998
AUTHORS
Jean-Pierre Chieze, DSMIDAPNIA/Service d' Astrophysique, CEA Saclay,
91191 Gif-sur-Yvette cedex 01, France
Fran~oise Combes, Observatoire de Paris, DEMIRM, 61 avenue de l'Observatoire,
75014 Paris, France
Edith Falgarone, Ecole Normale Superieure, Observatoire de Paris and CNRS,
24 rue Lhomond, 75005 Paris, France
Robert Kennicutt, Steward Observatory, University of Arizona, Tucson AZ 85721,
USA
Georges Meynet, Geneva Observatory, 1290 Sauvemy, Switzerland
Francesco Palla, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5,
50 125 Firenze, Italy
Joseph Silk, Departments of Astronomy and Physics, and Center for Particle
Astrophysics, University of California, Berkeley CA 94720, USA
FOREWORD
Starbursts are regions of unusually rapid star formation, often located in the central
parts of galaxies. They differ from more normal regions of star formation in terms of
the throughput of mass and the rapidity with which the gas is consumed. In the last
twenty years, extensive observational data at most wavelengths have become
available on starbursts, but many important issues remain to be addressed,
observationally as well as theoretically.
How are strong episodes of star formation triggered? What is the quantity of gas
converted into stars during bursts? What is the initial mass function of stars in these
events? How does the feedback from stars influence the interstellar medium and
self-regulate star formation? What is the subsequent chemical and photometric
evolution? How do starbursts rule the formation and evolution of galaxies?
In recent years, many observational data at different wavelengths (optical, radio,
infrared, X-ray) have become available. However, these observations are still
fragmentary in the sense that different classes of objects have been observed in
different ways, and the coverage is not consistently deep or complete. As a
consequence, an overall observational picture of starburst galaxies is missing, and
theoretical understanding and modelling have remained highly tentative. The
purpose of the school Starbursts: Triggers, Nature, and Evolution was to gather
theorists and observers with complementary approaches to the starburst
phenomenon, in order to summarize the state-of-the-art of the observations and
models, emphasizing the consistency of the various viewpoints.
Multiwavelength observations of starburst and "normal" galaxies now provide
interesting clues to the parameters ruling large-scale star formation. On smaller
scales, the hierarchy of gas clouds, from giant molecular clouds to compact cores,
has been observed in great detail and has begun to be theoretically understood. It is
now possible to address the formation of isolated and clustered stars, and to
understand the mechanisms of feedback to the interstellar medium. These new ideas
can also be studied through hydrodynamical simulations. The spectrophotometric
and chemical evolution of starburst and post-starburst stellar populations can be
followed, thanks to our knowledge of steiJar evolution for the whole range of
masses.
Extragalactic optical and infrared surveys have unveiled the increasing
importance of galaxy interaction and merging for the triggering of starbursts.
Numerical simulations now reproduce many original features of these galaxies,
including their disturbed morphologies and gas inflows fuelling the starbursts.
Finally, a consistent scenario of galaxy formation and evolution, which makes use of
these ideas in the cosmological paradigm of hierarchical structure formation,
is slowly emerging. In such an exciting context, we hope that the lecture
notes gathered in this volume will provide a better understanding of these
new insights into the physics of starbursts, and help in answering at least some of
the questions raised above.
VI
Acknawledgements
This session at the Centre de Physique des Houches and the present volume of
lecture notes could not have been achieved without the financial support of the
"Training and Mobility of Researchers" Programme of the European Commission
(contract ERB-4064-PL-95-0251), the Division of "Permanent Training" of the
Centre National de Ia Recherche Scientifique, the Inter-University Center for
Astronomy and Astrophysics (Pune), the Institute of Astrophysics (Paris), the
Division of Science and Technology ofthe Ministry of Foreign Affairs, the ACCES
Programme of the Ministry of Higher Education and Research, the Department of
Science and Technology of the Government of India, the French Embassy in Delhi,
and the University Joseph Fourier of Grenoble.
We are grateful to Alain Omont and Jayant Narlikar for advice in the critical
initial stages, to Michele Leduc for her help and continuous support, to Ghislaine
Chioso, Brigitte Rousset and Claire Simon for their patience and skill in the
management of the session, to Mme J. Fichard for her help, to Jyotsna Apte, Manjiri
Mahabal and Archana Kamnapure for secretarial assistance, and to Santosh
Khadilkar for help with the poster. Finally, this volume would not have existed
without the work and expertise of our lecturers, and without the presence of the
students, who came from various countries. They attended the lectures with
enthusiasm. We hope that these lecture notes, which hopefully will become a
standard reference in the field, will aid them in their research work.
Bruno Guiderdoni and Ajit Kembhavi
CONTENTS
LECTURE I
Fundamental Aspects of Star Formation in Galaxies
by R. Kennicutt
1. Introduction·······················'····································································· 1
2. Star formation properties of normal galaxies .... ....... ......... .............. .. .... .. 2
2.1. Quantitative diagnostics of star formation rates.............................. 2
2.2. SFRs of normal galaxies................................................................. 10
2.3. Interpretation: Star formation histories........................................... 12
3. The initial mass function......................................................................... 12
3.1. Introduction..................................................................................... 12
3.2. Nomenclature.................................................................................. 14
3.3. The solar neighborhood IMF .......................................................... 16
3.4. Galactic clusters and associations................................................... 17
3.5. The Magellanic Clouds................................................................... 20
3.6. Other galaxies................................................................................. 21
3.7. Conclusions..................................................................................... 23
4. Physical regulation of SFRs in galaxies .................................................. 25
4.1. Introduction..................................................................................... 25
4.2. The Schmidt law............................................................................. 25
4.3. Physical interpretation of the Schmidt law ..................................... 31
4.4. Star formation thresholds................................................................ 31
4.5. Gravitational stability thresholds .................................................... 31
4.6. Other threshold mechanisms........................................................... 35
LECTURE2
From Giant Molecular Clouds to Compact Cores
by E. Falgarone
1. Introduction . .. .. .. ..... ........... .. ..... .. ... ..... .......... ..... ..... ................ ......... .. ...... 41
2. The tracers of cold molecular material.................................................... 42
2.1. Molecular hydrogen: A tracer of the interface between dense
molecular gas and atomic gas in a UV-rich environment............... 42
VIII
2.2. Transitions of polar molecules: Tracers of density
and temperature.............................................................................. 44
2.3. The shapes and properties of the rotational line profiles: Tracers
of the velocity field .. .. .. . . . .. .. .. . .. .. . . . .. . . . . . ... .. .. .. . .. .. .. . . . .. .. .. . .. .. .. .. .. .. .. .. . 46
2.4. The thermal dust emission: Tracer of gas column density.............. 47
2.5. The tracers of magnetic field........................................................... 50
3. The local giant molecular clouds: comparison of their properties........... 53
3.1. Large-scale properties..................................................................... 54
3.2. Filamentary structures: Large and small-scale structures............... 56
3.3. The dense cores and the unseen scales............................................ 58
4. The· hierarchy of molecular clouds.......................................................... 62
5. The non-thermal energy densities of molecular complexes .................... 66
5.1. The turbulent velocity field............................................................. 66
5 .2. The coupling of the bulk of gas to the magnetic field..................... 71
6. Scenarios for generating cycles of star formation activity ...................... 71
7. Conclusions and perspectives.................................................................. 72
LECTURE3
Elements of Hydrodynamics
Applied to the Interstellar Medium
by J.-P. Chieze
1. Equations of fluid motion ............. ,.......................................................... 77
1.1. Mass conservation........................................................................... 77
1.2. Momentum conservation................................................................. 78
1.3. The stress tensor and viscosity........................................................ 81
1.4. Body forces..................................................................................... 85
1.5. Gravitation .. .. . .. . . . . .. .. .. .. . . . .. .. ... .. .. . .. .. . . . . . .. .. . .. .. . . . .. .. . . ... .. .. .. .. . .. . . . . .. . . .. . 86
1.6. The energy equation and dissipation............................................... 87
1.7. Entropy evolution............................................................................ 88
1.8. Fragmented systems of uniform energy density.............................. 88
2. Gas microphysics .................................................................................... 89
2.1. Coupling coefficients between plasma components........................ 89
2.2. Decay rate of the fluid momenta..................................................... 90
2.3. Rate of energy exchange between the two fluids............................ 90
2.4. Rate coefficients.............................................................................. 91
2.5. Post-shock relaxation in a low-density medium.............................. 93
2.6. Heat conduction .............................................................................. 93
CONTENTS IX
3. Inhomogeneous gas cooling.................................................................... 96
3.1. A multiphase model of the gas........................................................ 96
3.2. Mass-entropy spectrum................................................................... 97
LECTURE4
Isolated and Clustered Star Formation:
Observations and Theoretical Models
by F. Palla
I. Introduction ............................................................................................. I 0 I
3. Modes and distribution of star formation................................................ I 02
2.1. Stimulated star formation................................................................ I 02
2.2. Spontaneous star formation............................................................. 103
4. The quest for low-mass protostars........................................................... 104
3.1. Evolutionary properties of YSOs .................................................... I 04
3.2. Kinematic signatures of collapse.................................................... I 05
3.3. Outflows and jets............................................................................ I 07
5. The formation of high-mass stars............................................................ II 0
4.1. The evolution of ultracompact HII regions...................................... Ill
4.2. The search for massive protostars ................................................... 114
5. Isolated star formation............................................................................. 115
5 .I. Protostellar collapse: The mass accretion rate ............. ................... 116
5.2. Protostellar evolution...................................................................... 120
5.3. Early stellar evolution..................................................................... 122
6. Collective star formation ......................................................................... 123
6.1. The evidence for clustering............................................................. 126
6.2. Properties of clustering ................................................................... 127
LECTURES
Stellar Physics and Starburst Evolution
by G. Meynet
I. Introduction............................................................................................. 133
2. Stellar physics.......................................................................................... 134
2.1. Recall of some important processes in stellar evolution .. .. .. .. .. .. .. .. . 135
2.2. The evolutionary scenarios............................................................. 136
X
2.3. A few comments on some important physical ingredients
of stellar models.............................................................................. 138
3. Tests of stellar models............................................................................. 142
3.1. Pre-MS evolution of massive stars.................................................. 143
3.2. Stars on the main sequence............................................................. 144
3.3. Evolved massive stars..................................................................... 146
4. Massive star populations in galaxies....................................................... 148
4.1. The Wolf-Rayet stars...................................................................... 150
4.2. WR star populations in galaxies of the local group......................... 152
4.3. Massive star populations in starburst galaxies................................ 154
5. Chemical evolution.................................................................................. 161
5 .I. Nucleosynthetic sites, processes and time scales ...... ...................... 161
5.2. Metallicity dependence of the stellar yields.................................... 165
5.3. Chemical evolution in starbursts: the puzzling case of nitrogen..... 166
6. Conclusion............................................................................................... 168
LECTURE6
Starburst Triggering and Environmental Effects
by F. Combes
I. Introduction............................................................................................. 175
2. Stability of a two-fluid medium.............................................................. 176
3. Mechanisms to trigger starbursts............................................................. 178
4. Dynamical mechanisms: non-axisymmetry and torques ......................... 179
4.1 Angular momentum transfer for the stellar component .................. 179
4.2. Angular momentum transfer for the gas component....................... 181
4.3. Feedback and self-regulation.......................................................... 184
5. Fueling activity by bars........................................................................... 185
5.1. The inner Lindblad resonance......................................................... 186
5.2. Nuclear disks and nuclear bars........................................................ 188
5.3. Bar destruction through mass concentration ............ ....................... 189
5.4. Gas-dominated central disk............................................................. 190
6. Environmental effects.............................................................................. 190
6.1. Numerical codes and gas modelling............................................... 191
6.2. Star-formation processes................................................................. 191
6.3. Formation of large complexes......................................................... 192
6.4. Lessons from mergers..................................................................... 193
6.5. Gas morphology in mergers............................................................ 196