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Issue A&A Volume 448, Number 2, March III 2006 Page(s) L33 - L36 Section Letters DOI 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. Shukurov^{1, 2}, D. Sokoloff^{3, 2}, K. Subramanian² and A. Brandenburg<sup>4

1</sup>  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 -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

© ESO 2006

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