Dynamics of Galaxies , Giuseppe Bertin , Cambridge U. Press, New York, 2000. $95.00, $34.95 paper (414 pp.). ISBN 0-521-47262-8, ISBN 0-521-47855-3 paper
Giuseppe Bertin’s Dynamics of Galaxies is an elucidating account of a graduate course given by Bertin over the past two decades. It begins with a brief summary of galaxy morphology and kinematics and continues with a detailed theoretical description of spiral and elliptical galaxies. There is considerable discussion of the rationales for various mathematical approaches, including his own asymptotic and semiempirical models for spiral wave theory. Bertin also points out similarities between galaxy dynamics and other branches of physics such as fluid flow, plasma physics, and electrodynamics. Many of his descriptions are particularly good for beginning graduate students: his chapter on dispersive waves, for example. Each chapter includes thought-provoking questions.
The chapters on spiral density waves, modes, and spiral structure are similar in content and layout to Bertin’s monograph with C. C. Lin, Spiral Structure in Galaxies: A Density Wave Theory (MIT Press, 1996), with an expanded discussion of the modal theory based on the author’s work in the 1980s. Those chapters are the strongest sections of the book, emphasizing Bertin’s belief that “a study based on quasi-stationary spiral structure supported by intrinsic global modes gives a natural description of the observed large-scale [spiral] patterns and leads to a successful unified framework for the interpretation of the morphological categories of galaxies.” This interpretation partially reflects the limited range of solutions provided by existing analytical theory and symmetry assumptions; a much larger range of processes is thought to occur in real galaxies. For example, numerical models of galaxies, which are dismissed in this book as inherently limited, show a rich collection of additional phenomena that are not discussed here, including Alar Toomre’s spiral chaos from local instabilities; bar formation, stability, and dissolution; and tidal interactions. Nonlinear resonances between waves with different pattern speeds are also not discussed, although some galaxies, particularly those with bars, appear to have these resonances. Also omitted are purely gaseous processes, including star formation and turbulence, which produce realistic structures in numerical models.
The concentration on modal theory to the exclusion of more recent work limits the utility of this book for the general student. Other omissions are noteworthy too: In an observational section on new and future satellites, the most recent members of the great observatories, the Chandra x-ray telescope and the Space Infrared Telescope Facility, are not mentioned. The primary reference given for stellar population synthesis models is Reynier Peletier’s 1989 Groningen PhD thesis, but not the more recent and commonly used compendium by Claus Leitherer et al., called “Starburst 99,” which is freely available on the Web at http://coaticook.stsci.edu. In his section on classification systems, the author discusses the Hubble system and the Luminosity Class, but not the modification by Gerard de Vaucouleurs, which includes the important oval type SAB. The de Vaucouleurs system is the basis for the primary reference tabulation of important galaxy data, the Third Reference Catalogue of Bright Galaxies . Bertin also makes comments that might be obscure to someone new to the field, such as his saying that the 7 in an E7 galaxy comes from the observed aspect ratio of 3:1, rather than explaining that it comes from the expression 10(1 − b/a) = 7 for ratio of axes b/a = 1/3.
The other major text on this topic is James Binney and Scott Tremaine’s Galactic Dynamics (Princeton U. Press, 1987). Bertin’s book has more thorough explanations and derivations for much of the mathematics, particularly regarding the modal theory of spiral structure, and it has more recent material in some fields, such as dark matter in elliptical galaxies. But the scope in Binney and Tremaine is more comprehensive and the mathematics better trimmed for easy use. The two books evidently serve different purposes. Binney and Tremaine serve the interests of the general student, whereas Bertin’s book is particularly useful for students interested in mathematical methods of galactic dynamics. Bertin’s comparisons between galactic dynamics and plasma physics are also innovative and illustrative.
