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Galactic dynamos driven by magnetic buoyancy

Lookup NU author(s): Professor Anvar Shukurov, Professor Dmitry Sokoloff

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Abstract

We consider a mean field dynamo model for the generation of galactic magnetic fields, in which the driving mechanism for the alpha-effect is the buoyancy-driven Parker instability, rather than the conventional cyclonic turbulence. The dominant quenching mechanism is a buoyant velocity, which lifts field away from the disc plane. Our modified alpha-effect is essentially nonlinear, as its magnitude depends on the magnetic field strength. The dynamo thus exhibits threshold behaviour - the marginal dynamo number depends on the seed field geometry and strength. We investigate a basic one-dimensional 'slab' model both analytically and numerically, and also present results from a three dimensional calculation. In some ways our steady solutions resemble conventional galactic dynamo solutions, but the fields do not decrease so markedly away from the disc midplane, remaining strong out to the boundary of the dynamo region. The latter property is quite natural for a buoyancy driven system and may possibly be related to strong horizontal magnetic fields detected in the halos of some spiral galaxies.


Publication metadata

Author(s): Moss D, Shukurov A, Sokoloff D

Publication type: Article

Publication status: Published

Journal: Astronomy and Astrophysics

Year: 1999

Volume: 343

Issue: 1

Pages: 120-131

Print publication date: 01/01/1999

ISSN (print): 0004-6361

ISSN (electronic): 1432-0746

Publisher: EDP Sciences


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