Journal Article

The supernova-regulated ISM – II. The mean magnetic field

F. A. Gent, A. Shukurov, G. R. Sarson, A. Fletcher and M. J. Mantere

in Monthly Notices of the Royal Astronomical Society: Letters

Published on behalf of The Royal Astronomical Society

Volume 430, issue 1, pages L40-L44
Published in print March 2013 |
Published online December 2012 | e-ISSN: 1745-3933 | DOI:

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The origin and structure of the magnetic fields in the interstellar medium of spiral galaxies is investigated with 3D, non-ideal, compressible magnetohydrodynamic simulations, including stratification in the galactic gravity field, differential rotation and radiative cooling. A rectangular domain, 1 × 1 × 2 kpc3 in size, spans both sides of the galactic mid-plane. Supernova explosions drive transonic turbulence. A seed magnetic field grows exponentially to reach a statistically steady state within 1.6 Gyr. Following Germano (1992), we use volume averaging with a Gaussian kernel to separate magnetic field into a mean field and fluctuations. Such averaging does not satisfy all Reynolds rules, yet allows a formulation of mean-field theory. The mean field thus obtained varies in both space and time. Growth rates differ for the mean-field and fluctuating field and there is clear scale separation between the two elements, whose integral scales are about 0.7 and 0.3 kpc, respectively.

Keywords: dynamo; MHD; turbulence; ISM: kinematics and dynamics; galaxies: ISM

Journal Article.  3956 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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