Ebook Info
- Published: 2011
- Number of pages: 568 pages
- Format: PDF
- File Size: 4.81 MB
- Authors: Bruce T. Draine
Description
An essential resource for graduate students and astrophysicistsThis is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium―the gas and dust, as well as the electromagnetic radiation, cosmic rays, and magnetic and gravitational fields, present between the stars in a galaxy and also between galaxies themselves.Topics include radiative processes across the electromagnetic spectrum; radiative transfer; ionization; heating and cooling; astrochemistry; interstellar dust; fluid dynamics, including ionization fronts and shock waves; cosmic rays; distribution and evolution of the interstellar medium; and star formation. While it is assumed that the reader has a background in undergraduate-level physics, including some prior exposure to atomic and molecular physics, statistical mechanics, and electromagnetism, the first six chapters of the book include a review of the basic physics that is used in later chapters. This graduate-level textbook includes references for further reading, and serves as an invaluable resource for working astrophysicists.Essential textbook on the physics of the interstellar and intergalactic mediumBased on a course taught by the author for more than twenty years at Princeton UniversityCovers radiative processes, fluid dynamics, cosmic rays, astrochemistry, interstellar dust, and moreDiscusses the physical state and distribution of the ionized, atomic, and molecular phases of the interstellar mediumReviews diagnostics using emission and absorption linesFeatures color illustrations and detailed reference materials in appendicesInstructor’s manual with problems and solutions (available only to teachers)
User’s Reviews
Editorial Reviews: Review “This is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium. . . . This graduate-level textbook includes references for further reading, and serves as an invaluable resource for working astrophysicists.” ― Lunar and Planetary Information Bulletin Review “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 From the Back Cover “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 About the Author Bruce T. Draine is professor of astrophysical sciences at Princeton University and a member of the National Academy of Sciences. Excerpt. © Reprinted by permission. All rights reserved. Physics of the Interstellar and Intergalactic MediumBy Bruce T. DrainePRINCETON UNIVERSITY PRESSCopyright © 2011 Princeton University PressAll right reserved.ISBN: 978-0-691-12214-4ContentsPreface………………………………………………………………….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……………………………………………………………………529Chapter OneIntroduction 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 (i.e., starlight); radiation emitted by interstellar ions, atoms, and molecules; thermal emission from interstellar grains that have been heated by starlight; free–free emission (“bremsstrahlung”) from interstellar plasma; synchrotron radiation from relativistic electrons; and gamma rays emitted in nuclear transitions and π0 decays. • Interstellar magnetic field: The magnetic field resulting from electric currents in the interstellar medium; it guides the cosmic rays, and in some parts of the ISM, the magnetic field is strong enough to be dynamically important. • The gravitational field: This is due to all of the matter in the galaxy – ISM, stars, stellar remnants, and dark matter – but in some regions, the contribution of the ISM to the gravitational potential leads to self-gravitating clouds. • The dark matter particles: To the (currently unknown) extent that these interact nongravitationally with baryons, electrons, or magnetic fields, or either decay or annihilate into particles that interact with baryons, electrons, or magnetic fields, these are properly studied as part of the interstellar medium. The interactions are sufficiently weak that thus far they remain speculative. There is of course no well-defined boundary to a galaxy, and all of the preceding constituents are inevitably present between galaxies – in the intergalactic medium (IGM) – and subject there to the same physical processes that act within the interstellar medium. The purview of this book, therefore, naturally extends to include the intergalactic medium. The primary aim of this book is to provide the reader with an exposition of the physics that determines the conditions in, and evolution of, the interstellar medium and the intergalactic medium. We will also emphasize the ways that observational data (e.g., strengths of emission lines or absorption lines) can be used to determine the physical properties of the regions where the emission or absorption is occuring. We will employ the units of measurement that are currently used routinely by researchers in this field – for the most part, we use cgs units (including for electromagnetism), supplemented by standard astronomical units such as the parsec (pc), solar mass (M[??]), and solar luminosity (L[??]); see Table 1.1. Historically, astronomers have reported optical wavelengths in Ångstroms (Å). In recent years, much of the physics literature has shifted to nanometers (nm), and consideration was given to doing so here. After weighing pros and cons, I decided to stick with Ångstroms; in practical work, it is necessary to specify optical wavelengths to (at least) four digits to avoid confusion, and it seems easier to remember them without a decimal point. And, after all, conversion from Å to nm is simply division by 10, a rather minor concern in a field that measures distance in pc, brightnesses in magnitudes, and angles in degrees, arcminutes, and arcseconds. So this book will use Ångstroms for wavelengths shorter than 1 µm. I am, however, departing from established tradition by using wavelengths in vacuo for all transitions. This means that the wavelengths of familiar optical lines are now all shifted by ~1 Å – e.g., the famous [O III] doublet is now 4960, 5008, rather than the wavelengths in air (4959, 5007) that have been entrenched in usage for the past century. This will cause some pain for those who have burned the air wavelengths into their memories, but it is time to abandon this anachronism from days when spectroscopy was done in air at (near) standard temperature and pressure. 1.1 Organization of the ISM: Characteristic Phases In a spiral galaxy like the Milky Way, most of the dust and gas is to be found within a relatively thin gaseous disk, with a thickness of a few hundred pc (see the diagram in Fig. 1.2 and the images in Plates 1–5), and it is within this disk that nearly all of the star formation takes place. While the ISM extends above and below this disk, much of our attention will concern the behavior of the interstellar matter within a few hundred pc of the disk midplane. The Sun is located about 8.5 kpc from the center of the Milky Way; as it happens, the Sun is at this time very close to the disk midplane. The total mass of the Milky Way within 15 kpc of the center is approximately 1011 M[??]; according to current estimates, this includes ~5 x 1010 M[??] of stars, ~5 x 1010 M[??] of dark matter, and ~7 x 109> M[??] of interstellar gas, mostly hydrogen and helium (see Table 1.2). About 60% of the interstellar hydrogen is in the form of H atoms, ~20% is in the form of H2 molecules, and ~20% is ionized. The gaseous disk is approximately symmetric about the midplane, but does not have a sharp boundary – it is like an atmosphere. We can define the half-thickness z1/2 of the disk to be the distance z above (or below) the plane where the density has dropped to 50% of the midplane value. Observations of radio emission from atomic hydrogen and from the CO molecule indicate that the half-thickness z1/2 [approximately equals] 250 pc in the neighborhood of the Sun. The thickness 2z1/2 [nearly equals to] 500 pc of the disk is only ~6% of the ~8.5 kpc distance from the Sun to the Galactic center – it is a thin disk. The thinness of the distribution of dust and gas is evident from the 100 µm image showing thermal emission from dust in Plate 2, and the H I 21-cm line image in Plate 3. The baryons in the interstellar medium of the Milky Way are found with a wide range of temperatures and densities; because the interstellar medium is dynamic, all densities and temperatures within these ranges can be found somewhere in the Milky Way. However, it is observed that most of the baryons have temperatures falling close to various characteristic states, or “phases.” For purposes of discussion, it is convenient to name these phases. Here we identify seven distinct phases that, between them, account for most of the mass and most of the volume of the interstellar medium. These phases (summarized in Table 1.3) consist of the following: • Coronal gas: Gas that has been shock-heated to temperatures T [??] 105.5 K by blastwaves racing outward from supernova explosions. The gas is collisionally ionized, with ions such as O VI ([equivalent] O5+) present. Most of the coronal gas has low density, filling an appreciable fraction – approximately half – of the volume of the galactic disk. The coronal gas regions may have characteristic dimensions of 20 pc, and may be connected to other coronal gas volumes. The coronal gas cools on Myr time scales. Much of the volume above and below the disk is thought to be pervaded by coronal gas. It is often referred to as the “hot ionized medium,” or HIM. • H II gas: Gas where the hydrogen has been photoionized by ultraviolet photons from hot stars. Most of this photoionized gas is maintained by radiation from recently formed hot massive O-type stars – the photoionized gas may be dense material from a nearby cloud (in which case the ionized gas is called an H II region) or lower density “intercloud” medium (referred to as diffuse H II). Bright H II regions, such as the Orion Nebula, have dimensions of a few pc; their lifetimes are essentially those of the ionizing stars, ~3 – 10 Myr. The extended low-density photoionized regions – often referred to as the warm ionized medium, or WIM – contain much more total mass than the more visually conspicuous high-density H II regions. According to current estimates, the Galaxy contains 1.1×109 M of ionized hydrogen; about 50% of this is within 500 pc of the disk midplane (the distribution of the H II is discussed in Chapter 11). In addition to the H II regions, photoionized gas is also found in distinctive structures called planetary nebulae – these are created when rapid mass loss during the late stages of evolution of stars with initial mass 0.8M[??] Free Download Physics of the Interstellar and Intergalactic Medium (Princeton Series in Astrophysics, 19) in PDF formatKeywords
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