Astrophysics of Gaseous Nebulae
and Active Galactic Nuclei

Second Edition

Donald E. Osterbrock
Lick Observatory

Gary Ferland
University of Kentucky


Contents

Preface xii

Preface to First Edition xvi

1 General Introduction 1

1.1 Introduction 1

1.2 Gaseous Nebulae 1

1.3 Observational Material 4

1.4 Physical Ideas 10

1.5 Diffuse Nebulae 12

1.6 Planetary Nebulae 14

1.7 Nova and Supernova Remnants 16

1.8 Active Galactic Nucl ei 17

1.9 Star Formation in Galaxies 18

      References 22

2 Photoionization Equilibrium 29

2.1 Introduction 29

2.2 Photoionization and Recombination of Hydrogen 32

2.3 Photoionization of a Pure Hydrogen Nebula 35

2.4 Photoionization of a Nebula Containing Hydrogen and Helium 40

2.5 Photoionization of He+ to He++ 47

2.6 Further Iterations of the Ionization Structure 49

2.7 Photoionization of Heavy Elements 50

      References 60

3 Thermal Equilibrium 79

3.1 Introduction 79

3.2 Energy Input by Photoionization 80

3.3 Energy Loss by Recombination 81

3.4 Energy Loss by Free-Free Radiation 84

3.5 Energy Loss by Collisionally Excited Line Radiation 84

3.6 Energy Loss by Collisionally Excited Line Radiation of H 90

3.7 Resulting Thermal Equilibrium 91

      References 94

4 Calculation of Emitted Spectrum 118

4.1 Introduction 118

4.2 Optical Recombination Lines 120

4.3 Optical Continuum Radiation 131

4.4 Radio-Frequency Continuum and Line Radiation 136

4.5 Radiative Transfer Effects in H I 142

4.6 Radiative Transfer Effects in He I 150

4.7 The Bowen Resonance-Fluorescence Mechanisms for O III and O I 152

4.8 Collisional Excitation in He I 154

      References 157

5 Comparison of Theory with Observations 192

5.1 Introduction 192

5.2 Temperature Measurements from Emission Lines 194

5.3 Temperature Determinations from Optical Continuum Measurements 200

5.4 Temperature Determinations from Radio-Continuum Measurements 203

5.5 Temperature Determinations from Radio & UV Absorption Lines 207

5.6 Electron Densities from Emission Lines 210

5.7 Electron Temperatures and Densities from Infrared Emission Lines 215

5.8 Electron Temperatures and Densities from Radio Recombination Lines 216

5.9 Filling and Covering Factors 223

5.10 Ionizing Radiation from Stars 226

5.11 Abundances of the Elements in Nebulae 235

5.12 Calculations of the Structure of Model Nebulae 245

      References 250

6 Internal Dynamics of Gaseous Nebulae 283

6.1 Introduction 283

6.2 Hydrodynamic Equations of Motion 284

6.3 Free Expansion into a Vacuum 289

6.4 Shocks 291

6.5 Ionization Fronts and Expanding H+ Regions 295

6.6 Magnetic Fields 301

6.7 Stellar Winds 303

      References 306

7 Interstellar Dust 316

7.1 Introduction 316

7.2 Interstellar Extinction 316

7.3 Dust within H II Regions 325

7.4 Infrared Thermal Emission 331

7.5 Formation and Destruction of Dust Particles 337

7.6 Grain Opacities 339

7.7 Effects of Grains on Surrounding Gas 341

7.8 Dynamical Effects of Dust in Nebulae 345

      References 348

8 Infrared Radiation and Molecules 371

8.1 Introduction 371

8.2 The Structure of a PDR 372

8.3 The H2 Molecule 376

8.4 The CO Molecule 381

8.5 Comparison with Observations: 385

8.6 Molecules around H II Regions 389

      References 392

9 H II Regions in the Galactic Context 404

9.1 Introduction 404

9.2 Distribution of H II Regions in Other Galaxies 404

9.3 Distribution of H II Regions in Our Galaxy 406

9.4 Stars in H II Regions 410

9.5 Abundances of the Elements 413

9.6 Newly Formed Stars in H II Regions 424

9.7 Starburst Galaxies 427

      References 429

10 Planetary Nebulae 445

10.1 Introduction 445

10.2 Distance Determinations 445

10.3 Space Distribution and Kinematics of Planetary Nebulae 451

10.4 The Origin of Planetary Nebulae and the Evolution of Their Central Stars 453

10.5 The Expansion of Planetary Nebulae 461

10.6 Morphology and Composition 463

10.7 Planetary Nebulae with Extreme Abundances of the Elements 468

10.8 Molecules in Planetary Nebulae 470

10.9 Mass Return from Planetary Nebulae 474

10.10 Planetary Nebulae in Other Galaxies 476

       References 480

11 Heavy Elements and High-Energy Effects 502

11.1 Introduction 502

11.2 Physical Processes Involving Bound Electrons 502

11.3 Physical Processes at Still Higher Energies 508

11.4 Physical Conditions from X-ray Spectroscopy 513

11.5 Collisional Excitation of H0 518

      References 523

12 Nova and Supernova Remnants 537

12.1 Introduction 537

12.2 Nova Shells 537

12.3 The Crab Nebula 546

12.4 The Cygnus Loop 553

12.5 Cas A 559

12.6 Other Supernova Remnants 562

12.7 Spectroscopic Differences between Shock-Heated and Photoionized Regions 564

12.8  h Car 566

      References 570

13 Active Galactic Nuclei - Diagnostics and Physics 595

13.1 Introduction 595

13.2 Historical Sketch 597

13.3 Observational Classification of AGNs 601

13.4 Densities and Temperatures in the Narrow-Line Gas 608

13.5 Photoionization 613

13.6 Broad-Line Region 621

      References 628

14 Active Galactic Nuclei - Results 648

14.1 Introduction 648

14.2 Energy Source 649

14.3 Narrow-Line Region 653

14.4 LINERs 659

14.5 Broad-Line Region 663

14.6 Dust in AGNs 672

14.7 Internal Velocity Field 676

14.8 Physical Picture 685

      References 707

Appendix 1 Measures of Light 725

A1.1 Specific Intensity I 725

A1.2 Flux F 726

A1.3 Mean Intensity J 727

A1.4 Energy Density and Radiation Pressure 727

A1.5 Emittance 728

A1.6 Surface Brightness S 729

A1.7 Emissivity and Observed Quantities 729

      References 730

Appendix 2:  Milne Relation Between Capture and Photoionization Cross Sections 733

Appendix 3 Emission Lines of Neutral Atoms 736

Appendix 4 Nebular Quantum Mechanics 740

References 767

Appendix 5 Atomic Data for Heavy Element Ionization Balance 769

References 786

Appendix 6 Quantum Mechanics of Molecules 788

References 795

Glossary of Physical Symbols 796

Glossary of Acronyms 815

Index