Published in Planets, Stars and Stellar Systems Vol. 5, by Oswalt, Terry D.; Gilmore, Gerard, ISBN 978-94-007-5611-3. Springer Science+Business Media Dordrecht, 2013, p. 641
http://arxiv.org/abs/1302.5663

For a PDF version of the article, click here.

MAGNETIC FIELDS IN GALAXIES

Rainer Beck & Richard Wielebinski


Max-Planck-Institut für Radioastronomie, Bonn, Germany


Abstract: Most of the visible matter in the Universe is ionized, so that cosmic magnetic fields are quite easy to generate and due to the lack of magnetic monopoles hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in-situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic field is still under debate. The available data for external galaxies can well be explained by field amplification and ordering via the dynamo mechanism. The measured field strengths and the similarity of field patterns and flow patterns of the diffuse ionized gas give strong indication that galactic magnetic fields are dynamically important. They may affect the formation of spiral arms, outflows, and the general evolution of galaxies. In spite of our increasing knowledge on magnetic fields, many important questions on the origin and evolution of magnetic fields, their first occurrence in young galaxies, or the existence of large-scale intergalactic fields remained unanswered. The present upgrades of existing instruments and several radio astronomy projects have defined cosmic magnetism as one of their key science projects.


Keywords : Cosmic rays – dynamo action – Faraday rotation – Galactic Center – galaxies: radio emission – halos – interstellar medium – jets – magnetic fields: origin, evolution, strength, structure – Milky Way: radio emission – polarization – pulsars – radio telescopes – spiral arms – synchrotron emission – Zeeman effect


Table of Contents

INTRODUCTION

OBSERVATIONAL METHODS
Optical and far-infrared polarization
Synchrotron emission
Magnetic field components
Faraday rotation and Faraday depolarization
Zeeman effect
Field origin and amplification

MAGNETIC FIELDS IN THE MILKY WAY
Optical, far-infrared and sub-mm polarization
Radio continuum
Faraday Rotation of extra-galactic radio sources and pulsars
Zeeman effect
Modeling the magnetic field of the Milky Way

GALAXIES
Optical polarization, infrared polarization, and Zeeman effect
Magnetic field strengths
The radio - infrared correlation
Magnetic field structures in spiral galaxies
Magnetic fields in barred galaxies
Flocculent and irregular galaxies
Radio halos
Interacting galaxies
Galaxies with jets
Elliptical and dwarf spheroidal galaxies

OUTLOOK

APPENDIX
Catalogue of radio surveys of the Milky Way
Catalogue of radio polarization observations of nearby galaxies
Links to the SKA project and its precursor and pathfinder telescopes

REFERENCES

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