Magnetism, when extended beyond normal frameworks into cosmic space is characterized by an enormous spatial scale. Because of their large sizes the nature of magnets such as the Earth and the Sun is entirely different from the nature of a horseshoe magnet. The source of cosmic magnetism is associated with the hydrodynamic motions of a highly conductive medium. In this aspect, cosmic magnets resemble a dynamo. However, currents in the dynamo flow along properly ordered wires, while chaotic, turbulent motions are dominant inside stars and liquid planetary cores. This makes more intriguing and surprising the fact that these motions maintain a regular magnetic field. Maintenance of magnetic fields is even more impressive in huge magnets, i.e. galaxies. In fact, we are living inside a giant dynamo machine, the Milky Way galaxy. Although the idea of the global magnetic field of our Galaxy was clearly proposed almost 40 years ago, firm observational evidence and definite theoretical concepts of galactic magnetism have been developed only in the last decade. This book is the first attempt at a full and consistent presentation of this problem. We discuss both theoretical views on the origin of galactic magnetism and the methods of observational study. Previous discussions were on the level of review articles or separate chapters in monographs devoted to cosmic magnetic fields (see, e.g., H. K. Moffatt, 1978, E. N. Parker, 1979 and Zeldovich et aI., 1983).

Inhalt

I / Introduction.- II / Galaxies.- II. 1. Shapes.- II.2. Spiral Galaxies.- II.3. Gas and Dust.- II.4. Cosmic Rays.- III / Observation of Magnetic Fields.- III.1 Synchrotron Emission.- III.2. Polarization of Synchrotron Emission.- III.3. Faraday Rotation.- III.4. Light Polarization by Dust.- III.5. Zeeman Splitting.- III.6. Other Methods.- III.7. Discussion.- IV / Interpretation of Observational Data.- IV. 1. The Magic of Data Processing.- IV. 2. How the Magnetic Field is Derived from Faraday Rotation Data.- IV.3. The Large-scale Magnetic Field of the Galaxy According to Faraday Rotations of Extragalactic Sources.- IV.4. The Fluctuation Magnetic Field in the Galaxy.- IV.5. The Structure of the Large-Scale Field.- IV.6. Intensity Variations of the Galactic Non-thermal Radio Background.- IV.7. Magnetic Fields in Nearby Spiral Galaxies.- V / Origin of Magnetic Fields.- V.1. Introduction.- V.2. The Relic Field Hypothesis.- V.3. Cosmological Magnetic Fields.- V.4. Stellar Ejections.- V.5. The Dynamo.- VI / Galactic Hydrodynamics.- VI.1. Rotation.- VI.2. Shape of the Gaseous Disc.- VI.3. Interstellar Turbulence.- VI.4. Mean Helicity.- VI.5. Magnetic Fields and Star Formation.- VII / The Galactic Dynamo.- VII.1. Introduction.- VII.2. The Mean Magnetic Field.- VII.3. Evolution of Magnetic Field in a Moving Medium.- VII.4. The Equation for the Mean Magnetic Field.- VII.5. Field Distribution Across the Disc.- VII.6. Radial Field Distribution in Discs of Variable Thickness.- VII.7. Radial Distribution of Axisymmetric Fields in Spiral Galaxies.- VII.8. Generation of Non-Axisymmetric Magnetic Fields in an Axisymmetric Disc.- VII.9. The Origin of Large-Scale Bisymmetric Magnetic Structures.- VII.10. Large-Scale Magnetic Fields in Rigidly Rotating Objects.- VII.11. Magnetic Fields Within Spiral Arms.- VII.12. Non-linear Effects in the Galactic Dynamo.- VII.13. Generation of Fluctuation Fields.- VII.14. Seed Fields.- VIII / Magnetic Fields Around Galactic Discs.- VIII.1. Magnetic Fields in Gaseous Coronae.- VIII.2. Magnetic Fields in Clusters of Galaxies.- IX / Problems of Magnetic Field Generation in Galactic Nuclei, Quasars and Radiogalaxies.- IX.1. Center of the Galaxy.- IX.2. Quasars and Active Galactic Nuclei.- IX.3. Radiogalaxies.- IX.4. Jets.- X / Concluding Remarks.- References.