Über die Autorin bzw. den Autor

Bruce T. Draine is professor of astrophysical sciences at Princeton University and a member of the National Academy of Sciences.

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"This is the book that I have been waiting for for twenty years. With exceptional clarity, Draine introduces the underlying physics and brings the basic pieces together to describe the multiphase structure of the interstellar and intergalactic medium. Combined with many useful tables and figures, this book will rapidly become a hit with students and researchers alike. It continues the fine tradition of Princeton professors writing seminal books on this topic."--Ewine van Dishoeck, Leiden University

"A true tour de force, providing a definitive account of the physics of interstellar matter. Written with authority and insight by a master of the subject, Bruce Draine's book will be a treasured guide for new graduate students as well as a comprehensive and rigorous reference for galactic and extragalactic researchers."--Eve Ostriker, University of Maryland

"Draine has written an interstellar-medium textbook worthy of Lyman Spitzer, updated thirty years later. His coverage of atomic, molecular, radiative, thermal, and dynamical processes is excellent. Most valuable to students and professionals are the combinations of physical processes with multiwavelength observations appropriate for the modern astronomer."--J. Michael Shull, University of Colorado at Boulder

"This book is a comprehensive account of the physical processes that take place in the interstellar medium and that determine its behavior. It is likely to become the bible on the subject."--Alexander Dalgarno, Harvard University

"This is an outstanding text on an important topic in astrophysics. Draine carefully goes into the physical processes, providing a unifying discussion that is often missing in other treatments."--Christopher F. McKee, University of California, Berkeley

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Physics of the Interstellar and Intergalactic Medium

PRINCETON UNIVERSITY PRESS

Contents

Preface............................................................................xvii1. Introduction....................................................................12. Collisional Processes...........................................................113. Statistical Mechanics and Thermodynamic Equilibrium.............................224. Energy Levels of Atoms and Ions.................................................325. Energy Levels of Molecules......................................................386. Spontaneous Emission, Stimulated Emission, and Absorption.......................537. Radiative Transfer..............................................................638. H I 21-cm Emission and Absorption...............................................709. Absorption Lines: The Curve of Growth...........................................7510. Emission and Absorption by a Thermal Plasma....................................9211. Propagation of Radio Waves through the ISM.....................................10112. Interstellar Radiation Fields..................................................11913. Ionization Processes...........................................................12714. Recombination of Ions with Electrons...........................................13715. Photoionized Gas...............................................................16216. Ionization in Predominantly Neutral Regions....................................18217. Collisional Excitation.........................................................19018. Nebular Diagnostics............................................................20319. Radiative Trapping.............................................................21920. Optical Pumping................................................................22921. Interstellar Dust: Observed Properties.........................................23522. Scattering and Absorption by Small Particles...................................24823. Composition of Interstellar Dust...............................................26324. Temperatures of Interstellar Grains............................................28525. Grain Physics: Charging and Sputtering.........................................29626. Grain Dynamics.................................................................30427. Heating and Cooling of H II Regions............................................31528. The Orion H II Region..........................................................32629. H I Clouds: Observations.......................................................33130. H I Clouds: Heating and Cooling................................................33731. Molecular Hydrogen.............................................................34432. Molecular Clouds: Observations.................................................35733. Molecular Clouds: Chemistry and Ionization.....................................37334. Physical Processes in Hot Gas..................................................38135. Fluid Dynamics.................................................................38936. Shock Waves....................................................................39737. * Ionization/Dissociation Fronts...............................................41238. * Stellar Winds................................................................42239. Effects of Supernovae on the ISM...............................................42940. * Cosmic Rays and Gamma Rays...................................................44041. Gravitational Collapse and Star Formation: Theory..............................45142. Star Formation: Observations...................................................465A. List of Symbols.................................................................473B. Physical Constants..............................................................476C. Summary of Radiative Processes..................................................477D. Ionization Potentials (eV)......................................................481E. Energy-Level Diagrams...........................................................482F. Collisional Rate Coefficients...................................................496G. Semiclassical Atom..............................................................503H. Debye Length for a Plasma.......................................................505I. Heuristic Model for Ion–Electron Inelastic Scattering.....................506J. Virial Theorem..................................................................508Bibliography.......................................................................511Index..............................................................................529

Chapter One

The subject of this book is the most beautiful component of galaxies – the gas and dust between the stars, or interstellar medium. The interstellar medium, or ISM, is, arguably, also the most important component of galaxies, for it is the ISM that is responsible for forming the stars that are the dominant sources of energy. While it now appears that the mass of most galaxies is primarily in the form of dark matter particles that are collisionless, or nearly so, it is the baryons (accounting for perhaps ~10% of the total mass) that determine the visible appearance of galaxies, and that are responsible for nearly all of the energy emitted by galaxies, derived from nuclear fusion in stars and the release of gravitational energy in accretion disks around black holes. At early times, the baryonic mass in galaxies was primarily in the gas of the interstellar medium. As galaxies evolve, the interstellar medium is gradually converted to stars, and some part of the interstellar gas may be ejected from the galaxy in the form of galactic winds, or in some cases stripped from the galaxy by the intergalactic medium. Infalling gas from the intergalactic medium may add to the mass of the ISM. At the present epoch, the galaxy in which we reside – the Milky Way – has most of its baryons incorporated into stars or stellar remnants. But even today, perhaps 10% of the baryons in the Milky Way are to be found in the ISM. The "mass flow" of the baryons in the Milky Way is illustrated schematically in Figure 1.1.

Our objective is to understand the workings of the ISM – how it is organized and distributed in the Milky Way and other galaxies, what are the conditions (temperature, density, ionization, ...) in different parts of it, and how it dynamically evolves. Eventually, we would like to understand star formation, the process responsible for the very existence of galaxies as luminous objects.

The subject of this book, then, is everything in the galaxy that is between the stars – this includes the following constituents:

• Interstellar gas: Ions, atoms, and molecules in the gas phase, with velocity distributions that are very nearly thermal. • Interstellar dust: Small solid particles, mainly less than ~1 µm in size, mixed with the interstellar gas. • Cosmic rays: Ions and electrons with kinetic energies far greater than thermal, often extremely relativistic – energies as high as 10²¹ eV have been detected.

• Electromagnetic radiation: Photons from many sources, including the cosmic microwave background (CMB); stellar photospheres...