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Galactic dynamos with captured magnetic flux and an accretion flow

Lookup NU author(s): Professor Anvar Shukurov

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Abstract

We examine the behaviour of an axisymmetric galactic dynamo model with a radial accretion ow in the disc. We also introduce a vertical magnetic flux through the galactic midplane, to simulate the presence of a large scale magnetic field trapped by the galaxy when forming. The trapped vertical flux is conserved and advected towards the disc centre by the radial flow. We confirm that accretion flows of magnitude several kms(-1) through a significant part of the galactic disc can markedly inhibit dynamo action. Moreover, advection of the vertical flux in general results in mixed parity galactic fields. However, the effect is nonlinear and non-additive - global magnetic field energies are usually significantly smaller that the sum of purely dynamo generated and purely advected field energies. For large in ow speeds, a form of "semi-dynamo" action may occur. We apply our results to the accumulation and redistribution, by a radial in ow, of a vertical magnetic flux captured by the Galactic disc. Taking representative values, it appears difficult to obtain mean vertical fields near the centre of the Milky Way that are much in excess of 10 muG, largely because the galactic dynamo and turbulent magnetic diffusion modify the external magnetic field before it can reach the disc centre.


Publication metadata

Author(s): Moss D, Shukurov A

Publication type: Article

Publication status: Published

Journal: Astronomy & Astrophysics

Year: 2001

Volume: 372

Issue: 3

Pages: 1048-1063

ISSN (print): 0004-6361

ISSN (electronic): 1432-0746

Publisher: EDP Sciences

URL: http://dx.doi.org/10.1051/0004-6361

DOI: 10.1051/0004-6361


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