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Issue A&A
Volume 374, Number 1, July IV 2001
Page(s) 36 - 41
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010601



A&A 374, 36-41 (2001)
DOI: 10.1051/0004-6361:20010601

Generation of bisymmetric magnetic fields in galaxies with tidal interaction

A. Vögler1, 2 and D. Schmitt1, 3

1  Universitäts-Sternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
2  Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
3  Copernicus Gesellschaft, Max-Planck-Str. 13, 37191 Katlenburg-Lindau, Germany
    e-mail: egs@copernicus.org

(Received 11 August 2000 / Accepted 23 April 2001)

Abstract
Tidal interactions between neighbouring galaxies are expected to induce significant nonaxisymmetric velocities in their disks. It has been suggested that these velocities play an important role in the generation of bisymmetric magnetic fields observed in interacting galaxies. We investigate the effect of a nonaxisymmetric radial outflow on a three-dimensional linear mean field dynamo. We find that the usually dominant axisymmetric quadrupole is effectively damped by the outflow. For sufficiently high velocities a bisymmetric magnetic mode is then preferentially excited. The resulting field has a spiral-arm structure extending well into the differentially rotating outskirts of the disk. The influence of velocity-induced mode-coupling effects on bisymmetric field generation is found to be negligible. While being highly idealized, the model seems to give reasonable representations of the large scale fields of the interacting galaxies M 81 and M 51.


Key words: galaxies: magnetic fields; interactions -- magnetic fields -- MHD

Offprint request: A. Vögler, avoegler@linmpi.mpg.de

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