Magnetic field structure in differentially rotating discs |
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Authors: | K J Donner A Brandenburg |
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Institution: | Observatory and Astrophysics Laboratory , University of Helsinki , T?htitorninm?ki, SF-00130, Helsinki, Finland |
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Abstract: | Abstract In order to gain a better understanding of the processes that may give rise to non-axisymmetric magnetic fields in galaxies, we have calculated field decay rates for models with a realistic galactic rotation curve and including the effects of a locally enhanced turbulent magnetic diffusivity within the disc. In all cases we have studied, the differential rotation increases the decay rate of non-axisymmetric modes, whereas axisymmetric ones are unaffected. A stronger magnetic diffusivity inside the disc does not lead to a significant preference for non-axisymmetric modes. Although Elsasser's antidynamo theorem has not yet been proved for the present case of a non-spherical distribution of the magnetic diffusivity, we do not find any evidence for the theorem not to be valid in general. |
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Keywords: | Galactic magnetic fields hydromagnetics disc dynamos Elsasser theorem |
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