Astron. Astrophys. 335, 789-796 (1998)

Symmetry and direction of seed magnetic fields in galaxies

F. Krause ^{1, 2} and R. Beck <sup>2

1</sup> Alice-Bloch-Strasse 14, D-14558 Bergholz-Rehbrücke, Germany
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received 25 November 1997 / Accepted 6 March 1998

Abstract

Radio observations of large-scale magnetic fields in spiral galaxies suggest that these fields show in many cases a dominating S0 symmetry, i.e. even symmetry to the central plane and axisymmetry with respect to the rotational axis. In addition, detailed evaluation of Faraday rotation measures in five nearby galaxies reveals that in four cases the magnetic field lines are directed toward the centre of these galaxies. Dynamo theory, successful in explaining the existence of such fields, does not contain any statement concerning the sign of the field which depends on the initial conditions. Hence we investigate whether there is a mechanism which produces seed fields with a definitely determined field direction. Neither pre-galactic seed fields, nor galactic battery seed fields, nor ionization fronts are able to imprint such a dominating direction.

Key words: magnetic fields galaxies: formation galaxies: magnetic fields early Universe radio continuum: galaxies

Send offprint requests to: R. Beck

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations of large-scale fields
  • 2.1. Symmetries
  • 2.2. Radial directions
• 3. Large-scale magnetic fields in a pregalactic cosmos
• 4. Magnetic seed fields in a rotating disk formed by the Biermann-battery effect
  • 4.1. Magnetic seed fields due to differential rotation
  • 4.2. Large-scale magnetic seed fields due to small-scale motions
• 5. Ionization fronts crossing density fluctuations
• 6. Discussions and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
helpdesk@link.springer.de