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Galactic magnetic fields and spiral arms
3D dynamo simulations
D. Elstner 1,
K. Otmianowska-Mazur 2,
S. von Linden 3 and
M. Urbanik 2
Received 11 August 1999 / Accepted 25 February 2000
We investigate the evolution of three-dimensional (3D), large-scale galactic magnetic fields under the influence of time dependent gas flows in spiral arms and excited by a turbulent dynamo. Our principal goal is to check how the enhanced turbulent diffusion in spiral arms affects the global magnetic field structure evolving under the influence of the dynamically changing gaseous spiral arms. Self-consistent N-body simulations of a two-component, self-gravitating disk provide the time-dependent gas velocity, which is used as the large scale velocity field in the induction equation in addition to the turbulent electromotive force. Using the beam-smoothed polarization models the results of our simulations are confronted with observed configurations of polarization B-vectors in nearby galaxies.
The magnetic field is found to be directly influenced by large-scale non-axisymmetric flows yielding the magnetic field locally well-aligned with gaseous spiral arms. Large pitch angles, similar to those of gaseous arms are found to propagate into the interarm region, too. However, in our models a decrease of magnetic pitch angles still occurs in the interarm region. It may be due to a diffusion coefficient between spiral arms too low to counteract the outward gas flows in these regions trying to turn the magnetic vectors to pitch angles of an opposite sign. A too weak effect is also possible, probably because of a lack of extended diffusive halo at this stage of our model.
Key words: Magnetohydrodynamics (MHD) turbulence ISM: magnetic fields galaxies: ISM
Send offprint requests to: D. Elstner
Online publication: May 3, 2000