Astron. Astrophys. 326, 465-476 (1997)

Observational signatures of helical galactic magnetic fields

M. Urbanik ¹, D. Elstner ² and R. Beck <sup>3

1</sup> Astronomical Observatory, Jagiellonian University, Krakow, Poland
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
³ Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany

Received 28 February 1997 / Accepted 23 May 1997

Abstract

We investigate the possibility of reproducing the observed polarization and Faraday rotation properties of spiral galaxies assuming their disks to be filled with regular helical magnetic fields. Both small-scale ( 1 kpc) flux tubes predicted by local hydrodynamic models and global, galaxy-scale (several kpc) fields generated by the dynamo process are considered. The large-scale fields are found to well reproduce the observed regular spiral pattern of polarization B vectors, as well as asymmetries of Faraday rotation and low-frequency polarization, often believed to signify non-axisymmetric or bisymmetric fields.

Key words: galaxies: magnetic fields galaxies: spiral radio continuum: galaxies polarization galaxies: individual: NGC 6946 MHD

Send offprint requests to: M. Urbanik

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Contents

• 1. Introduction
• 2. Model description
  • 2.1. General assumptions
  • 2.2. Magnetic field structures
  • 2.3. Methods of modeling
• 3. Results
  • 3.1. High-frequency distributions of the polarized intensity
  • 3.2. The effects of Faraday depolarization
  • 3.3. Faraday rotation measures
• 4. Discussion
• 5. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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