1996/10/22 by M. Hanasz, Hanasz, M., H. Lesch +1
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Astrophysics and Star Formation Studies #Geomagnetism and Paleomagnetism Studies #Solar and Space Plasma Dynamics #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9610167
LaTeX, 15 pages, 8 figures, uses l-aa.sty and epsf.sty, minor corrections to match the published version, Published in Astronomy & Astrophysics, 321, 1007
arxiv created 1997/11/23 · arxiv updated 2009/12/01
In this paper we investigate the idea of Hanasz & Lesch 1993 that the galactic dynamo effect is due to the Parker instability of magnetic flux tubes. In addition to the former approach, we take into account more general physical conditions in this paper, by incorporating cosmic rays and differential forces due to the axisymmetric differential rotation and the density waves as well. We present the theory of slender magnetic flux tube dynamics in the thin flux tube approximation and the Lagrange description. This is the application of the formalism obtained for solar magnetic flux tubes by Spruit (1981), to the galactic conditions. We perform a linear stability analysis for the Parker-shearing instability of magnetic flux tubes in galactic discs and then calculate the dynamo coefficients. We present a number of new effects which are very essential for cosmological and contemporary evolution of galactic magnetic fields. First of all we demonstrate that a very strong dynamo α-effect is possible in the limit of weak magnetic fields in presence of cosmic rays. Second, we show that the differential force resulting from axisymmetric differential rotation and the linear density waves causes that the α-effect is essentially magnified in galactic arms and switched off in the interarm regions. Moreover, we predict a non-uniform magnetic field in spiral arms and well aligned one in interarm regions. These properties are well confirmed by recent observational results by Beck & Hoernes (1996)