S ROPHYSIC S LIBRARY LIBRARY - Springer978-1-4612-3936... · 2017. 8. 26. · LIBRARY ASTRC) OMY A 0 ASTRC)PHYSI S LIBR RY Series Editors: M. Harwit, R. Kippenhahn, J.-P. Zahn Tools

LIBRARY

A TRC) OMY A D

S ROPHYSIC S LIBRARY

Series Editors: M. Harwit, R. Kippenhahn, l-P. Zahn

~~tv'bER ~TUD}: ~1~'Of-J

Advisory Board:

IN. Bahcall P.L. Biermann S. Chandrasekhar S.M. Faber L.V. Kuhi P.G. Mezger P.A. Strittmatter

LIBRARY

ASTRC) OMY A 0

ASTRC)PHYSI S LIBR RY

Series Editors: M. Harwit, R. Kippenhahn, J.-P. Zahn

Tools of Radio Astronomy K. Rohlfs

Physics of the Galaxy and Interstellar Matter H. Schemer and H. Elsasser

Galactic and Extragalactic Radio Astronomy, 2nd Edition G.L. Verschuur and K.I. Kellermann, Editors

Astrophysical Concepts, 2nd Edition M. Harwit

Observational Astrophysics P.Lena

G.L.Verschuur K.I. Kellermann Editors With the Assistance of E. Bouton

Galactic and Extragalactic Radio Astronomy Second Edition

With 207 Figures

Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona Budapest

Gerrit L. Verschuur

Kenneth I. Kellermann

National Radio Astronomy Observatory, Charlottesville, VA 2290\, USA

Series Editors

Martin Harwit National Air and Space Museum Smithsonian Institution 7th SI. and Independence Ave. S.W. Washington, D.C. 20560, USA

Rudolf Kippenhahn Max-Planck-Institut fUr Physik und Astrophysik Institut fUr Astrophysik Karl-Schwarzschild-Stral3e 1 D-8046 Garching, Fed. Rep. of Germany

lean-Paul Zahn Universite Paul Sabatier Observatoires du Pic-du-Midi et de Toulouse 14, Avenue Edouard-Belin F-314OQ Toulouse, France

Corer picture: The Elliptical Radio Galaxy M87 (Virgo A) jet and lobe structure. The image shows the complex filamentary structure as well as the radio jet (to the upper right of the image). (Observers: F.N. Owen. D.C. Hines. Courtesy NRAOjAUI.)

Library of Congress Cataloging-in-Publication Data Galactic and extragalactic radio astronomy.

(Astronomy and astrophysics library) Rev. ed. of: Galactic and extra-galactic radio

astronomy. 1974. Bibliography: p. Includes index. 1. Radio astronomy. I. Verschuur, Gerrit L.,

1937- . II. Kellermann, Kenneth I., 1937-III. Galactic and extra-galactic radio astronomy. IV. Series. QB475.AIG35 1988 522'.682 87-24340 © 1974, 1988 by Springer-Verlag New York Inc.

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ISBN-13:978-0-387-97735-5 e-ISBN-13:978-1-4612-3936-9 DOl: 10.1007/978-1-4612-3936-9

Preface

Galactic and Extragalactic Radio Astronomy, Second Edition discusses radio observations of the universe beyond the solar system. It is intended for graduate students and practicing astronomers who wish to familiarize themselves with the wealth of astronomical phenomena that are "visible" at radio frequencies. The subject matter and general level essentially follow that of the first edition, but the content has been brought up to date to reflect the enormous growth in radio astronomy during the past 15 years. Indeed, the impact of radio observations of astronomical phenomena is now so great that the individual chapters could each be expanded into an entire book. Within the restraints of page limits, the authors have tried to emphasize fundamental ideas and to provide a guide to the literature for more detailed concepts. As in our previous book, the emphasis and completeness of the chapters reflects the interests and style of the individual authors.

The chapters have been reviewed by independent referees and we wish to thank E.M. Berkhuijsen, L. Blitz, J.M. Cordes, D.P. Cox, J. Crovisier, P.J. Diamond, J.R. Dickel, D.E. Hogg, W.M. Irvine, P.e. Myers, B. Partridge, R. Porcas, M.S. Roberts, R. Sancisi, and P.A. Shaver for their very substantial contributions which have improved the accuracy and clarity of the text. We also wish to thank P. Smiley, P. Weems, G. Kessler, R. Monk, and B. Cassell for their careful work in preparing the illustrative material, and the many secretaries involved who so carefully prepared the manuscript, and the National Radio Astronomy Observatory for its support throughout the preparation of this book. One of us (GLV) is particularly grateful to Drs. H. Hvatum and P. Vanden Bout. The National Radio Astronomy Observatory is operated by Associated Universities, Inc. under contract with the National Science Foundation.

GERRIT L. VERSCHUUR

KENNETH I. KELLERMANN

Contents

Preface ................................... , ........ " . . . . . . .. . . . v Contributors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi

1. Galactic Nonthermal Continuum Emission CHRIS J. SALTER and ROBERT L. BROWN

1.1 Introduction ............................................. . 1.1.1 Historical Preface .................................... . 1.1.2 Early Surveys of Galactic Radio Emission ................ .

a. Angular Distribution ofthe Cosmic Radio Waves ......... . b. Spectral Distribution of the Cosmic Radio Waves ......... . c. The Situation Circa-1956 .............................. .

1.2 Physical Processes ........................................ . 1.2.1 Synchrotron Radiation ................................ .

a. Single Partic1e Emission ............................... . b. Radiation from an Ensemble of Particles ................. . c. Influence of the Medium .............................. .

1.2.2 The Faraday Effect ................................... . 1.3 Total Intensity Observations of the Galactic Radio

Continuum .............................................. . 1.3.1 The Medium-Resolution Surveys ....................... . 1.3.2 High-Resolution Surveys of the Galactic Plane ........... . 1.3.3 The Galactic Loops and Spurs ......................... . 1.3.4 The Nonthermal Radiation and Galactic Structure ........ . 1.3.5 A Galactic Radio Halo? ............................... .

1.4 The Spectrum of the Nonthermal Emission ................... . 1.4.1 The Galactic Spectrum Above 10 MHz .................. . 1.4.2 The Very-Low-Frequency Spectrum .................... . 1.4.3 The Energy Spectrum of Cosmic-Ray Electrons ........... .

1.5 Linear Polarization of the Nonthermal Emission ............... . 1.5.1 Surveys of Linear Polarization of the Galactic Emission .... . 1.5.2 Implications for the Local Magnetic Field ................ . 1.5.3 Magnetic Fields in the Galactic Loops ................... . 1.5.4 Rotation Measure Data and the Galactic Magnetic Field ... .

1.6 The Galactic Nonthermal Radiation in Perspective ............. . Recommended Reading .......................................... . References ..................................................... .

1 1 1 3 3 5 6 6 6 7 9

10 11

12 13 15 15 18 22 23 24 25 26 28 28 30 31 32 33 34 34

viii Contents

2. HII Regions and Radio Recombination Lines MARK A. GORDON ......................................... 37

2.1 Ionized Interstellar Hydrogen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.1.1 Emission Nebulae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.1.2 Diffuse Thermal Background ........................... 38

2.2 Radiation Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.3 Continuum Thermal Emission (Bremsstrahlung) . . . . . . . . . . . . . . . . 40

2.3.1 Absorption and Emission Coefficients. . . . . . . . . . . . . . . . . . . . 40 2.3.2 Transfer Equation for Continuum Radiation .............. 41 2.3.3 Low-Frequency Radiation from HII Regions. . . . . . . . . . . . . . 42 2.3.4 High-Frequency Radiation from HII Regions. . . . . . . . . . . . . . 42 2.3.5 Integrated Observations of HII Regions .................. 42 2.3.6 Reality and the "Homogeneous Nebula" Approximation .... 43 2.3.7 Continuum Observations ofHII Regions. . . . .. . . . . .. . . . . . 44 2.3.8 Thermal Emission from Dust ........................... 45

2.4 Basic Theory of Radio Recombination Lines ................... 46 2.4.1 Line Frequencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 2.4.2 Shape Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.4.3 Absorption and Emission Coefficients . . . . . . . . . . . . . . . . . . . . 50 2.4.4 Transfer Equation for Line Radiation .................... 52

2.5 Refinements to the Transfer Equations ........................ 53 2.5.1 Local Thermodynamic Equilibrium. . . . . . . . . . . . . . . . . . . . . . 53 2.5.2 Departures from LTE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 2.5.3 Turbulence Broadening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 2.5.4 Pressure Broadening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

2.6 Single-Dish Observations of Radio Recombination Lines from HII Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 2.6.1 Early Observations ofIntegrated Line Intensities. . . . . . . . . . . 59 2.6.2 Non-LTE Density-Gradient Models. . . .. . . .. . .. . . .. . .. . . 62 2.6.3 Clumped Models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 2.6.4 Comparison of the Density-Gradient and Clumped Models. . 65 2.6.5 Empirical Determinations of Electron Temperature. . . . . . . . . 67

2.7 Exploration of the Milky Way by Radio Recombination Lines. .. . 68 2.7.1 Galactic Distribution of HII Regions. . . . . . . . . . . . . . . . . . . . . 68 2.7.2 Galactocentric Variations of Electron Temperatures. . . . . . . . 71 2.7.3 Abundance Ratio of Helium to Hydrogen. . . . . . . . . . . . . . . . . 71 2.7.4 The Diffuse Component. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

2.8 Radio Observations of HII Regions with High Angular Resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 2.8.1 Continuum Observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 2.8.2 Recombination-Line Observations. . . . . . . . . . . . . . . . . . . . . . . 82

2.9 Other Aspects of Radio Recombination Lines .................. 83 2.9.1 Low Frequencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 2.9.2 Zeeman Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 2.9.3 The Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Contents ix

2.9.4 Planetary Nebulae .................................... 88 2.9.5 Dark Clouds ......................................... 88 2.9.6 Galaxies and Quasars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

RecommendedReading. ... ... ... .... ....... ...... .... ............ 92 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

3. Neutral Hydrogen and the Diffuse Interstellar Medium SHRINIVAS R. KULKARNI and CARL HEILES ..................... 95

3.1 Introduction: Fundamentals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 3.1.1 Radiative Transfer and Excitation of the HI Line. . . . . . . . . . . 96 3.1.2 Observations of the Diffuse Medium ..................... 101

a. Brief Review of the Four Phases: CNM, WNM, WIM, HIM. 101 b. Galactic Distribution of HI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

3.1.3 Interstellar Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 a. Excitation of CI Fine Structure. . . . . . . . . . . . . . . . . . . . . . . . . . 105 b. Excitation of the CII Fine-Structure Lines ................ 106 c. Pressure of the WIM .................................. 106

3.1.4 Theory of the Kinetic Temperature of Diffuse Interstellar Gas................................................. 107

a. Cooling Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 b. Heating Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 c. The Equilibrium Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . 110 d. Is Statistical Equilibrium Always Obtained? . . . . . . . . . . . . . . . 111

3.1.5 Elements of Interstellar Gas Dynamics ................... 111 a. Static Equilibrium: The z-Structure in the Galaxy ... . . . . . . . 112 b. Static Equilibrium: A Uniform Spherical Magnetized Cloud. 112 c. Transient Features: Shocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

3.1.6 Two Famous Models of the Interstellar Medium. . . . . . . . . . . 115 3.2 Structure of the Diffuse Interstellar Medium: HI Emission. . . . . . . . 118

3.2.1 Low-Velocity Gas.. . ... . . ... ... . ... .... .. . . ... . . .. . .. . 118 a. Shells ............................................... 118 b. Filaments.................................... . . . . . . . . 122 c. Major HI Concentrations Around Dark Clouds

and Newly Formed Stars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 d. Shapes of HI Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 e. Structure of HI Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

3.2.2 Intermediate-Velocity Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 3.2.3 Supershells and "Worms" .............................. 126

3.3 Temperature and Ionization of the Diffuse Interstellar Medium ... 126 3.3.1 HI Absorption: Techniques, Data, and Analysis. . . . . . . . . . . . 126

a. Techniques and Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 b. Derived Spin Temperature: Definition and Limitations. . . . . . 128

3.3.2 Temperature of Warm HI .............................. 129 3.3.3 Temperature of the Cold HI (CNM). . . . . . . . . . . . . . . . . . . . . . 131

x Contents

a. Classical Absorption Studies: The T-r Relation ............ 131 b. Statistics of Clouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

3.3.4 Temperature Structure of HI Clouds. . . . . . . . . . . . . . . . . . . . . 133 a. Temperature Structure and the T-r Relation. . . . . . . . . . . . . . . 134 b. PhysicalImplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

3.3.5 Ionization of the Diffuse Interstellar Medium. . . . . . . . . . . . . . 135 a. Observations......................................... 135 b. Ionization Within Diffuse Clouds. . . . . . . . . . . . . . . . . . . . . . . . 137 c. Where Do the Electrons Reside? . . . . . . . . . . . . . . . . . . . . . . . . . 137 d. The Energy Source for the WIM . . . . . . . . . . . . . . . . . . . . . . . . . 138

3.3.6 Filling Factors of the WIM, WNM, and CNM.......... ... 140 3.4 Interstellar Magnetic Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

3.4.1 Methods of Measurement .............................. 142 a. B J.: Linear Polarization of Starlight . . . . . . . . . . . . . . . . . . . . . . 142 b. B.l: Linear Polarization of Synchrotron Radiation. . . . . . . . . . 142 c. B.l: Linear Polarization of Radio-Wavelength Spectral Lines. 143 d. B II : Faraday Rotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 e. B II : Zeeman Splitting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 f. Faraday Rotation Versus Zeeman Splitting ............... 144

3.4.2 Fields in External Galaxies ............................. 144 3.4.3 The Galactic Field on Scales Above 100 pc . . . . . . . . . . . . . . . . 144

a. The Field Strength .................................... 144 b. The Field Direction ................................... 146

3.4.4 The Galactic Field on Scales of 100 pc and Below. . . . . . . . . . 147 3.5 Summary................................................. 149

Recommended Reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

4. Molecules as Probes of the Interstellar Medium and of Star Formation BARRY E. TURNER.... .... . .......... . ....... ... . ... ... . .... 154

4.1 Introduction .............................................. 154 4.1.1 Historical Perspective. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 4.1.2 The Central Role of Molecular Spectroscopy . . . . . . . . . . . . . . 155

4.2 The Large-Scale Morphology of the ISM ...................... 158 4.2.1 The Physical Regimes of the ISM. ... ... . ... .... ... ...... 158

a. "Coronal" Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 b. Intercloud Gas ....................................... 158 c. Diffuse Interstellar Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 d. Cold Dark Clouds .................................... 160 e. Globules............................................. 160 f. Giant Molecular Clouds ............................... 160 g. Hot Molecular Cores in GMCs ......................... 161

4.2.2 The Morphology of Dense Molecular Clouds. . . . . . . . . . . . . . 162 4.2.3 GMCs and Spiral Arms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Contents xi

4.3 The Nature of Star-Forming Regions ......................... 165 4.3.1 Small Star-Forming Cores in SMCs and GMCs. . . . . . . . . . . . 165 4.3.2 Massive Star-Forming Cores in GMCs . . . . . . . . . . . . . . . . . . . 166 4.3.3 Large-Scale Relationships of Star-Forming Regions ........ 167

a. Low-Mass-Star-Forming Regions ....................... 168 b. Massive-Star-Forming Regions. . . . . . . . . . . . . . . . . . . . . . . . . . 169

4.3.4 Intermediate-Scale Structure: Velocity Outflows and Disks .. 170 4.3.5 Magnetic Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 4.3.6 Small-Scale Structure of Star-Forming Regions . . . . . . . . . . . . 174

a. The Orion Molecular Core ............................. 174 b. Other Star-Forming Cores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

4.3.7 A Summary of Star Formation Morphology. . . .. . . . .. . .. . . 179 4.4 The Stability of Molecular Clouds and Cores. . . . . . . . . . . . . . . . . . . 180

4.4.1 Star Formation Rates and the Stability of Molecular Clouds. 180 4.4.2 Global Relations Between (n, L, Av) for Molecular Clouds ... 180 4.4.3 Rotation..................................... . . . . . . . . 182 4.4.4 Magnetic Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 4.4.5 Stellar Winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 4.4.6 "Gravito-Turbulence" or "Star Cloud Turbulence" ......... 183

4.5 The Formation of Stars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 4.5.1 Low-Mass Stars from Low-Mass Cores. . . . . . . . . . . . . . . . . . . 184 4.5.2 Formation of Massive Stars from Massive Cores. . . . . . . . . . . 185

a. A Summary of Observational Constraints. . . . . . . . . . . . . . . . . 185 b. Massive-Star Formation: Enhanced Accretion plus Shocks .. 187

4.5.3 A Stochastic Picture of Star Formation. . . . . . . . . . . . . . . . . . . 188 4.6 Future Prospects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

4.6.1 High-Resolution Studies of Star Formation ............... 190 a. Global Aspects As Seen in Other Galaxies ................ 190 b. Star-Forming Cores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 c. The Question of the Elusive "Proto star" . . . . . . . . . . . . . . . . . . 191 d. Ori(KL) and Detailed Studies of Star-Forming Regions. . . . . 192

4.6.2 Submillimeter and Far-IR Studies ....................... 192 a. Far-IR Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 b. Submillimeter Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

Recommended Reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

5. Interstellar Molecules and Astrochemistry BARRY E. TURNER and Lucy M. ZIURYS . . . . . . . . . . . . . . . . . . . . . . . 200

5.1 Molecules in Space: An Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 5.1.1 A Brief History ....................................... 200 5.1.2 The Presently Known Interstellar Molecules .............. 204 5.1.3 Interstellar Chemistry: Some Generalities. . . . . . . . . . . . . . . . . 206

5.2 Where Molecules Are Found: Basic Morphology of the Dense Interstellar Medium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

xii Contents

5.2.1 Diffuse Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 5.2.2 Envelopes of GMCs and SMCs ("Dark Clouds") . . . . . . . . . . . 211 5.2.3 Cold Cores and Low-Mass Star-Forming Cores

in Molecular Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 5.2.4 Warm Massive Cores in GMCs ......................... 214 5.2.5 Shocked Regions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 5.2.6 Circum stellar Envelopes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

5.3 Molecular Abundances and Their Determination ............... 219 5.3.1 Method of Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

a. The Simplest Derivation of Column Densities ............. 220 b. Elementary Column Density Estimates When Many

Transitions Are Observed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 c. Column Density Estimates from Radiative Transfer

Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 5.3.2 Problems in Abundance Determinations. . . . . . . . . . . . . . . . . . 223

a. Clumping..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 b. Fractional Abundances ................................ 224 c. Collisional Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 d. Kinetic Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 e. Radiation Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

5.3.3 Representative Abundances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 5.4 The Four Basic Schemes of Interstellar Chemistry. . . . . . . . . . . . . . . 226

5.4.1 Ion-Molecule Chemistry ............................... 230 5.4.2 Surface Chemistry on Dust Grains . . . . . . . . . . . . . . . . . . . . . . . 235

a. Difficulties for Grain-Surface Chemistry: Diffuse and Cold Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

b. Grain-Surface Chemistry in Warm Clouds. . . . . . . . . . . . . . . . 237 c. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

5.4.3 Shock Chemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 5.4.4 Circum stellar Chemistry ............................... 241

a. Carbon-Rich Envelopes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 b. Oxygen-Rich Envelopes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 c. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

5.5 Current Dilemmas and Future Directions. . . . . . . . . . . . . . . . . . . . . . 244 5.5.1 The Composition ofInterstellar Dust Grains . . . . . . . . . . . . . . 244 5.5.2 Diffuse Bands ........................................ 245 5.5.3 Synthesis of Complex Molecules. . . . . . . . . . . . . . . . . . . . . . . . . 246 5.5.4 Ring Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 5.5.5 NO Bonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 5.5.6 Chemistry Involving Second- and Third-Row Elements ..... 248 5.5.7 "Biological" Molecules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 5.5.8 Unidentified Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 5.5.9 A Final Perspective: What Has Astrochemistry Revealed? ... 249


Contents xiii

6. Astronomical Masers MARK J. REID and JAMES M. MORAN . . . . . . . . . . . . . . . . . . . . . . . . . . 255

6.1 Introduction .............................................. 255 6.2 Maser Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

6.2.1 Radiative Transfer .................................... 257 6.2.2 Input Sources ........................................ 262 6.2.3 Geometry and Apparent Sizes. . . . . . . . . . . . . . . . . . . . . . . . . . . 263 6.2.4 Saturation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 6.2.5 Line Widths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 6.2.6 Polarization.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 6.2.7 Pump Models ........................................ 269

a. Interstellar Maser Pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 b. Stellar Maser Pumps .................................. 273

6.3 Interstellar Masers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 6.3.1 H 2 0 Masers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 6.3.2 on Masers .......................................... 278

6.4 Stellar Masers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 6.4.1 Supergiants .......................................... 287

6.5 Extragalactic Masers ....................................... 288 6.6 Interstellar Scattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 6.7 Distance Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

Recommended Reading ..................... , . .. . . ... . .. . . . .. . . .. . 293 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

7. The Structure of Our Galaxy Derived from Observations of Neutral Hydrogen

W. BUTLER BURTON ........................................ 295 7.1 Observations of Galactic Neutral Hydrogen. . . . . . . . . . . . . . . . . . . . 295 7.2 Kinematics of Galactic Neutral Hydrogen ..................... 303

7.2.1 Velocities Due to Differential Galactic Rotation. . . . . . . . . . . . 303 7.2.2 The Galactic Rotation Curve ........................... 305 7.2.3 Galactic Constants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 7.2.4 Deviations from Circular Symmetry and Circular Motions .. 317

7.3 Mapping the Galaxy Using Neutral Hydrogen Observations. . . . . . 322 7.3.1 Line Profile Characteristics Caused by Geometrical Effects .. 322 7.3.2 Profile Characteristics Caused by Kinematic Irregularities . . . 324 7.3.3 Some Remarks on the Spiral Structure of the Galaxy ....... 326

7.4 The Inner-Galaxy Gas Layer ................................ 328 7.4.1 Radial Distribution of the Inner-Galaxy Gas and

Dust Layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 7.4.2 Thickness and Flatness of the Inner-Galaxy Gas and

Dust Layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 7.4.3 Other Parameters of the Inner-Galaxy Gas and Dust Layer. . 337

7.5 The Outer-Galaxy Gas Layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

xiv Contents

7.5.1 The Shape of the Warped, Flaring, Outer-Galaxy Gas Layer. .. . . . . ... . . . .. . . .. . . .. . . . .. . . .. . .. . .. .. . . .. . .. 340

7.5.2 Some Characteristics of the Warped Gas Layer in Other Galaxies ... : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

7.5.3 Brief Remarks on the Phenomenon of High-Velocity Clouds. . . . . .. . . . .. . . . .. . . ... . .. . . . .. . .. . .. . . .. . . .. . . 350


8. The Galactic Center HARVEY S. LISZT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

8.1 Introduction and Apologia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 8.2 Radio Continuum Emission from the Provinces of Sagittarius. . . . . 360

8.2.1 Sgr D ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360 8.2.2 Sgr B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360 8.2.3 Sgr C ............................................... 362 8.2.4 Sgr E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 8.2.5 Taking Stock of the Situation in the Provinces. . . . . . . . . . . . . 364

8.3 Sgr A and Its Immediate Environment ........................ 365 8.3.1 The Compact Source Sgr A * . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 8.3.2 Sgr A East Is Both East and West ....................... 368 8.3.3 Sgr A West. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

a. A Massive Rotating Ring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 b. A Small "Bar" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

8.3.4 Sgr A * Redux ........................................ 372 8.3.5 All the King's Horses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372

8.4 Material in Sgr A Observed on 10- to 50-pc Scales .............. 372 8.5 The Neutral Gas Reservoir in the Inner Galactic Regions ........ 374

8.5.1 The "Expanding 3-kpc Arm" . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 8.5.2 A Tilted Disk - The Galaxy's Bar? . . . . . . . . . . . . . . . . . . . . . . . 374 8.5.3 More on the Central Gas Reservoir. . . . . . . . . . . . . . . . . . . . . . 376


9. Radio Stars ROBERT M. HJELLMING.. . . . .. . . . .. . . .. . .. . . .. . .. . . . .. . . .. . . . 381

9.1 The Early Years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381 9.1.1 The Search for the Radio Sun. . . . . . . . . . . . . . . . . . . . . . . . . . . 381 9.1.2 Early Flare Star Observations. . . . . . . . . . . . . . . . . . . . . . . . . . . 382 9.1.3 When Is a Star a Radio Star? ........................... 382 9.1.4 The "Twilight" Years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 9.1.5 The Dawn of Stellar Radio Astronomy. . . . . . . . . . . . . . . . . . . 385

9.2 Fundamental Radio Emission Processes and Stellar Radiative Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 9.2.1 Radiative Transfer in Stellar Environments. . . . . . . . . . . . . . . . 386

Contents xv

9.2.2 Fundamental Radiation Processes . . . . . . . . . . . . . . . . . . . . . . . 389 a. Thermal Bremsstrahlung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 b. Magneto-Bremsstrahlung .............................. 389 c. Thermal Versus Nonthermal and Incoherent Versus

Coherent ............................................ 391 9.3 Solar Radio Emission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

9.3.1 Types of Solar Radio Emission. . . . . . . . . . . . . . . . . . . . . . . . . . 391 9.3.2 Quiet Sun Emission and the Slowly Varying Component. . . . 392 9.3.3 Enhanced Radio Emission Associated with Sunspots and

Active Regions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 9.3.4 Solar Noise Storms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 9.3.5 Solar Radio Bursts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

a. Radio Emission Associated with First-Stage Flares . . . . . . . . . 396 b. Radio Emission Associated with Second-Stage Flares . . . . . . . 397

9.3.6 The Solar Wind. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 9.4 Flare Stars and Active Binaries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

9.4.1 Flare Star Radio Emission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 9.4.2 "Radio-Active" Binaries-Particularly RS CVn's. . . . . . . . . . . 400 9.4.3 Pre-Main-Sequence Stars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405

9.5 Stellar Winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 9.5.1 Ionized Stellar Winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 9.5.2 Stellar Wind Observables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 9.5.3 Cool, Weakly Ionized Winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 407 9.5.4 VV Cephei Binaries-Ionized Subregions of Cool Supergiant

Winds............................................... 407 9.5.5 Symbiotic Stars-Interacting Winds and Ionized

Subregions of Winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 9.6 Cataclysmic Variables ...................................... 409

9.6.1 Classical Novae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 9.6.2 Recurrent Novae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 9.6.3 Dwarf Novae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 9.6.4 Magnetic Cataclysmic Variables. . . . . . . . . . . . . . . . . . . . . . . . . 415

9.7 Radio-Emitting X-Ray Binaries .............................. 416 9.7.1 Summary of Major Radio-Emitting X-Ray Binaries ....... 416 9.7.2 Relativistic Jets and Synchrotron Flaring in Cyg X-3 ...... 417

a. Cyg X-3 as a Sychrotron Flaring Source. . . . . . . . . . . . . . . . . 417 b. Cyg X-3 as a Relativistic Jet Source . . . . . . . . . . . . . . . . . . . . . 420

9.7.3 Periodic Radio Variations in Cir X-I, LSI +61°303, and Cyg X-3 ............................................ 420

9.7.4 Relativistic Jets in SS433 .............................. 421 9.7.5 Evolving Bubbles, Layers, and Cones of Relativistic

Electrons ........................................... 426 a. Type of Geometry for Synchrotron-Radiating Regions. . . . . 426 b. Radio-Emitting Bubbles and Layers with Spherical

Symmetry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 c. Evolution of Conical Radio Jets . . . . . . . . . . . . . . . . . . . . . . . . 429

xvi Contents

9.7.6 Sco X-1-Radio Variable with Companion Double Radio Source...... . ............ . ................ ......... 431

9.7.7 The Very Large Remnants Around SS433 and Cir X-1 ..... 431 9.7.8 Other X-Ray Binaries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 9.7.9 Transient X-Ray/Radio Stars. . . . . . . . . . . . . . . . . . . . . . . . . . 433 9.7.10 A Unified View of Radio-Emitting X-Ray Binaries. . . . . . . . . 433

9.8 Future Work on Radio Stars ................................ 434 Recommended Reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

10. Supernova Remnants STEPHEN P. REYNOLDS .................................... 439

10.1 Introduction............................................ 439 10.1.1 History........................................... 439

10.2 Supernovae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 10.2.1 Type I and Type II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 10.2.2 Rates.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444

10.3 Observed Properties of Supernova Remnants. . . . . . . . . . . . . . . . . 445 10.3.1 Radio Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 10.3.2 Optical Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 10.3.3 X-Ray Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 10.3.4 Variability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456 10.3.5 Statistics of Supernova Remnants. . . . . . . . . . . . . . . . . . . . . 457 10.3.6 Radio Supernovae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

10.4 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 10.4.1 Evolution......................................... 460 10.4.2 Relation of Evolutionary Theory to Observations . . . . . . . 465 10.4.3 Crablike Supernova Remnants. . . . . . . . . . . . . . . . . . . . . . . 466 10.4.4 Nonthermal Emission from Supernova Remnants. . . . . . . 468 10.4.5 Radio Supernovae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

10.5 Collective Interactions of Supernova Remnants with the Galaxy................................................. 473 10.5.1 Structure ofthe Interstellar Medium .................. 473 10.5.2 Energy and Mass Input into the Interstellar Medium .... 473 10.5.3 Cosmic Rays ......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474

10.6 Future Prospects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 Recommended Reading. .. .... . .... . ... ... . ... ..... ... .... .... ... . 476 Catalogues of Galactic Supernova Remnants. . . . . . . . . . . . . . . . . . . . . . . . . 476 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

11. Pulsars DON C. BACKER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

11.1 Introduction ............................................ 480 11.1.1 Brief History of Neutron Stars. ... ... . ........... .... 480 11.1.2 New Types of Pulsars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481

Contents xvii

11.2 Basic Properties ......................................... 482 11.2.1 Intensity Spectra. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 11.2.2 Dispersion and Distance Scale ....................... 482 11.2.3 Pulse Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484 11.2.4 Standard Model of Emission Mechanism .............. 484

11.3 Pulse Morphology and Polarization ........................ 485 11.3.1 Pulse Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485 11.3.2 Polarization....................................... 487 11.3.3 Hollow-Cone Beam Model . . . . . . . . . . . . . . . . . . . . . . . . . . 487 11.3.4 More Polarization Effects ........................... 489 11.3.5 A Beam Model .................................... 490 11.3.6 Interpulses and Steady Emission. . . . . . . . . . . . . . . . . . . . . . 490

11.4 Intensity Fluctuations .................................... 491 11.4.1 Micropulses....................................... 491 11.4.2 Subpulses......................................... 492 11.4.3 Periodic Subpulse Phenomena ....................... 493 11.4.4 Pulse Nulling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493 11.4.5 Other Modulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

11.5 Interstellar Propagation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 11.5.1 Neutral Hydrogen Absorption ....................... 496 11.5.2 Thermal Plasma Dispersion ......................... 496 11.5.3 Birefringence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497 11.5.4 Secular Variations of Path Integrals. . . . . . . . . . . . . . . . . . . 498 11.5.5 Diffraction Caused by Interstellar Turbulence .......... 498

a. Thin-Screen Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 b. Pulse Broadening ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501 c. Scintillation....................................... 501 d. Scattering Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503

11.5.6 Refraction by Interstellar Turbulence. . . . . . . . . . . . . . . . . . 503 11.6 Timing and Astrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504

11.6.1 Time of Arrival Measurements. . . . . . . . . . . . . . . . . . . . . . . 504 11.6.2 Time of Arrival Analysis ............................ 504 11.6.3 Interpretation of Pulsar Spin Properties ............... 506 11.6.4 Astrometry.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507

11. 7 Binary and Millisecond Pulsars ............................ 508 11. 7.1 The New Pulsars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508 11.7.2 Timing a Binary Pulsar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508 11. 7.3 Timing a Millisecond Pulsar . . . . . . . . . . . . . . . . . . . . . . . . . 511

11.8 Radio Emission Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 11.8.1 Basic Requirements ................................ 513 11.8.2 Emission Site.... .... . ... . . ... ... . ... .. . . .. . . . ... . . 514 11.8.3 Polar-Cap Models ................................. 514

11.9 Origin and Evolution. . . ... . . ... . . .. . ... . ... .... . .. . . ... . . 515 11.9.1 Introduction...................................... 515 11.9.2 Galactic Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 11.9.3 Period Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517

xviii Contents

11.9.4 Binary Pulsar Evolution ........................... . Recommended Reading .......................................... . References ..................................................... .

12. Extragalactic Neutral Hydrogen RICCARDO GIOVANELLI and MARTHA P. HAYNES

12.1 Introduction ........................................... . 12.1.1 The Role of Neutral Hydrogen in Galaxies ............ . 12.1.2 The Information in the 21-cm Line ................... . 12.1.3 Pictorial Presentation of HI Data .................... .

12.2 The Distribution of HI in Galaxies ......................... . 12.2.1 Morphology ..................................... . 12.2.2 Sizes ............................................ . 12.2.3 Warps ........................................... . 12.2.4 Appendages ...................................... .

12.3 Velocity Fields ......................................... . 12.3.1 Rotation Curves .................................. . 12.3.2 Distortions in the Velocity Field ..................... . 12.3.3 The Mass Distribution in Spiral Galaxies ............. . 12.3.4 Dark Matter in Dwarf Galaxies ..................... .

12.4 The Velocity Width as a Distance Indicator ................. . 12.4.1 The Velocity Width-Magnitude Relation ............. . 12.4.2 Deviations from Hubble Flow ....................... .

12.5 HI Content and Other Global Properties ................... . 12.5.1 Relations Between Global Properties for Spirals (Sa and

Later) ........................................... . 12.5.2 HI Content of Early-Type Galaxies .................. .

12.6 Environmental Effects ................................... . 12.6.1 Tidal Interactions ................................. . 12.6.2 Gas Deficiency in Cluster Spirals .................... .

12.7 Cosmological Studies .................................... . 12.7.1 21-cm Redshift Surveys ............................ . 12.7.2 Voids and the Segregation of Galaxian Properties ...... . 12.7.3 HI in Active Galaxies .............................. . 12.7.4 HI in Quasars and in Their Spectra .................. .

Recommended Reading .......................................... . References ..................................................... .

13. Radio Galaxies and Quasars KENNETH I. KELLERMANN and FRAZER N. OWEN ............. .

13.1 Introduction ........................................... . 13.1.1 Optical Counterparts .............................. .

a. Historical Background ............................. . b. Radio Galaxies ................................... . c. Quasars ......................................... .

519 520 520

522 522 522 523 527 528 528 530 531 532 534 534 536 537 540 541 541 543 544

544 546 547 548 549 550 551 552 555 557 560 560

563 563 563 565 565 566

Contents xix

13.1.2 Radio Source Properties ............................ 568 13.1.3 Radio Spectra. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569 13.1.4 Energy Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

13.2 Low-Luminosity Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 13.2.1 Spiral, Seyfert, and Irregular Galaxies. . . . . . . . . . . . . . . . . 575 13.2.2 Elliptical Galaxies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576

13.3 Compact Sources ........................................ 576 13.3.1 Self-Absorption ................................... 576 13.3.2 Inverse Compton Radiation ......................... 577 13.3.3 Polarization....................................... 579 13.3.4 Structure ......................................... 580 13.3.5 Variability........................................ 581 13.3.6 Source Dynamics and Superluminal Motion. . . . . . . . . . . . 585 13.3.7 Relativistic Beaming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588

13.4 Extended Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591 13.4.1 Jets, Lobes, and Hot Spots. . . . . . . . . . . . . . . . . . . . . . . . . . . 592 13.4.2 Jet Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597

a. Straight Jets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 b. Bent Jets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598

13.5 Summary............................................... 599 Recommended Reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600

14. The Microwave Background Radiation JUAN M. USON and DAVID T. WILKINSON.................... 603

14.1 Introduction ............................................ 603 14.1.1 The Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603 14.1.2 Cosmological Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603

14.2 The Spectrum of the Microwave Background. . . . . . . . . . . . . . . . . 605 14.2.1 Summary......................................... 605 14.2.2 Heterodyne Radiometer Methods (A ~ 3 mm) .......... 607 14.2.3 Bolometric Measurements (A ~ 3 mm) . . . . . . . . . . . . . . . . . 612 14.2.4 Measurements Using Interstellar Molecules. . . . . . . . . . . . 615 14.2.5 Summary and Future Prospects. . . . . . . . . . . . . . . . . . . . . . 616

14.3 Polarization of the Microwave Background. . . . . . . . . . . . . . . . . . 617 14.4 Anisotropy Searches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618

14.4.1 Small-Scale Measurements .......................... 618 a. A Scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618 b. Measurements..................................... 621 c. Constraints on Cosmological Models ................. 625 d. Near-Future Improvements. . . . . . . . . . . . . . . . . . . . . . . . . . 626

14.4.2 Measurements of Large-Scale Structure. . . . . . . . . . . . . . . . 627 a. A Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 b. Measurements..................................... 629 c. Likely Near-Future Improvements. . . . . . . . . . . . . . . . . . . . 630

xx Contents

14.5 The Sunyaev-Zel'dovich Effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 14.5.1 Concept and Cosmological Consequences. . . . . . . . . . . . . . 632 14.5.2 Measurements....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635 14.5.3 Cosmological Applications .......................... 637


15. Radio Sources and Cosmology JAMES 1. CONDON. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641

15.1 Introduction........................................... 641 15.2 Basic Relations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642 15.3 The "Wodd Picture" and Source Evolution . . . . . . . . . . . . . . . . . 643 15.4 Source Population Data ................................. 646

15.4.1 The Local Luminosity Function. . . . . . . . . . . . . . . . . . . . . 646 15.4.2 Source Counts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649 15.4.3 Spectral-Index Distributions. . . . . . . . . . . . . . . . . . . . . . . . 652 15.4.4 RedshiftjSpectral-Index Diagrams ................... 653 15.4.5 Redshift and Luminosity Distributions of Strong

Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653 15.4.6 Optical Constraints ............................... 653

15.5 Evolutionary Models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656 15.5.1 Source Distribution Equations. . . . . . . . . . . . . . . . . . . . . . 657 15.5.2 Evolutionary Models of Radio Luminosity Functions. . . 658

15.6 Source Size Evolution ................................... 662 15.6.1 The Angular Size-Redshift Relation. . . . . . . . . . . . . . . . . . 662 15.6.2 The Angular Size-Flux Density Data. . . . . . . . . . . . . . . . . 664 15.6.3 Models of the Angular Size-Flux Density Relation ..... 665

15.7 The Faint-Source Population. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667 15.8 Isotropy and Homogeneity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669 15.9 Cosmology Made Simple: The Shell Model ................. 671 15.10 What Next? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675


Index. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . . .. . . .. . . . . . . . . . . . . . 679

Contributors

DON C. BACKER, Radio Astronomy Laboratory, University of California at Berkeley, Berkeley, California, USA

ROBERT L. BROWN, National Radio Astronomy Observatory, Charlottesville, Virginia, USA

W. BUTLER BURTON, University of Leiden, Sterrewacht Leiden, 2300 RA Leiden, The Netherlands

lAMES 1. CONDON, National Radio Astronomy Observatory, Charlottesville, Virginia, USA

RICCARDO GIOVANELLI, National Astronomy and Ionosphere Center, Arecibo Observatory, Arecibo, Puerto Rico

MARK A. GORDON, National Radio Astronomy Observatory, Tucson, Arizona, USA

MARTHA P. HAYNES, National Astronomy and Ionosphere Center, Astronomy Department, Cornell University, Ithaca, New York, USA

CARL HEILES, Astronomy Department, University of California at Berkeley, Berkeley, California, USA

ROBERT M. HJELLMING, National Radio Astronomy Observatory, Socorro, New Mexico, USA

KENNETH I. KELLERMANN, National Radio Astronomy Observatory, Charlottesville, Virginia, USA

SHRINIVAS R. KULKARNI, Henry M. Robinson Laboratory of Astrophysics, California Institute of Technology, Pasadena, California, USA

HARVEY S. LISZT, National Radio Astronomy Observatory, Charlottesville, Virginia, USA

JAMES M. MORAN, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA

XXII Contributors

FRAZER N. OWEN, National Radio Astronomy Observatory, Soccoro, New Mexico, USA

MARK J. REID, Radio and Geoastronomy, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA

STEPHEN P. REYNOLDS, North Carolina State University, Department of Physics, Raleigh, North Carolina, USA

CHRIS J. SALTER, National Radio Astronomy Observatory, Charlottesville, Virginia, USA

BARRY E. TURNER, National Radio Astronomy Observatory, Charlottesville, Virginia, USA

JUAN M. USON, National Radio Astronomy Observatory, Socorro, New Mexico, USA

DAVID T. WILKINSON, Princeton University, Joseph Henry Laboratories, Department of Physics, Princeton, New Jersey, USA

Lucy M. ZIURYS, Five College Radio Astronomy Observatory, University of Massachusetts, Amherst, Massachusetts, USA

Documents

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