Dynamos in discs and halos of galaxies.
Abstract
The authors investigate linear and nonlinear dynamo models for a galactic disc embedded in a halo, assuming a relatively strong magnetic diffusivity and a non-vanishing α effect in the halo. They take the halo to be spherical and embedded in a vacuum. The field is assumed to be axisymmetric, but they do not impose symmetry conditions at the equatorial plane. In one parameter regime mixed parity solutions are found. However, it is argued that the regular magnetic field in the galactic halo can hardly reach a steady-state configuration during the galactic lifetime. In the regime that is observably relevant the field can have an even parity within and near the disc and an odd one in the halo. This may have implications for explaining the occurrence of a neutral sheet above the galactic plane. During certain time intervals the rotation measure of these models shows a doubly peaked azimuthal variation, which could be falsely interpreted as an indication of a bisymmetric field structure.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 1992
- Bibcode:
- 1992A&A...259..453B
- Keywords:
-
- Disk Galaxies;
- Dynamo Theory;
- Galactic Halos;
- Interstellar Magnetic Fields;
- Spiral Galaxies;
- Astronomical Models;
- Magnetic Diffusion;
- Turbulent Diffusion;
- Astrophysics