To be published in Acta Astronomica Sinica Vol. 44, 2003 (Conf. Proc. "Radio Studies of Galactic Objects, Galaxies and AGNs", eds. J.L. Han et al.).
astro-ph/0304245

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RADIO OBSERVATIONS OF THE MAGNETIC FIELDS IN GALAXIES

M. Krause

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 68, D-53121 Bonn, Germany


Abstract. After a short introduction on how we get information of the magnetic fields from radio observations I discuss the results concerning the magnetic field structure in galaxies: Large-scale regular magnetic field pattern of spiral structure exist in grand-design spirals, flocculent and even irregular galaxies. The regular field in spirals is aligned along the optical spiral arms but strongest in the interarm region, sometimes forming `magnetic arms'. The strongest total field is found in the optical arms, but mainly irregular. The large-scale regular field is best explained by some kind of dynamo action. Only a few galaxies show a dominant axisymmetric field pattern, most field structures seem to be a superposition of different dynamo modes or rather reveal more local effects related to density waves, bars or shocks. Observations of edge-on galaxies show that the magnetic fields are mainly parallel to the disk except in some galaxies with strong star formation and strong galactic winds as e.g. NGC 4631.


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