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Issue A&A
Volume 448, Number 2, March III 2006
Page(s) L33 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200600011

A&A 448, L33-L36 (2006)
DOI: 10.1051/0004-6361:200600011

Letter

Galactic dynamo and helicity losses through fountain flow

A. Shukurov1, 2, D. Sokoloff3, 2, K. Subramanian2 and A. Brandenburg4

1  School of Mathematics and Statistics, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK
    e-mail: anvar.shukurov@ncl.ac.uk
2  Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007, India
3  Department of Physics, Moscow University, 119992 Moscow, Russia
4  Nordita, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark

(Received 23 December 2005 / Accepted 19 January 2006)

Abstract
Aims. Nonlinear behaviour of galactic dynamos is studied, allowing for magnetic helicity removal by the galactic fountain flow.
Methods. A suitable advection speed is estimated, and a one-dimensional mean-field dynamo model with dynamic $\alpha$-effect is explored.
Results. It is shown that the galactic fountain flow is efficient in removing magnetic helicity from galactic discs. This alleviates the constraint on the galactic mean-field dynamo resulting from magnetic helicity conservation and thereby allows the mean magnetic field to saturate at a strength comparable to equipartition with the turbulent kinetic energy.


Key words: magnetic fields -- turbulence -- ISM: magnetic fields -- galaxies: ISM





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