Astronomy and Astrophysics – Astronomy
Scientific paper
May 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989mnras.238..621c&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 238, May 15, 1989, p. 621-648.
Astronomy and Astrophysics
Astronomy
20
Dynamo Theory, Galactic Rotation, Interstellar Magnetic Fields, Magnetic Field Configurations, Spiral Galaxies, Continuous Radiation, Disk Galaxies, Faraday Effect, Linear Polarization, Radio Emission
Scientific paper
General considerations are given to the global modes of magnetic fields generated by the galactic dynamo. The standard disk dynamo equations are extended to include the generation of azimuthal field components via the alpha-effect, which is important in central regions of some galaxies (e.g. M51) where the shear of galactic rotation is weak. Attention is focused on the nonaxisymmetric modes (m = 1 modes) to compare them with the observed bisymmetric magnetic fields. Although growing m = 1 modes do exist, they tend to grow more slowly than the axisymmetric modes with m = O. Their eigenfunctions are confined within narrow regions in the radial direction of a disk. Thus, using the standard galactic dynamo, it is still difficult to explain the dominance of the bisymmetric fields and to reproduce their coherent structure extending over a disk by a single m = 1 mode. The growth rate of m = 1 modes depends on the thickness of the disk; it is higher in a thin disk than in a thick disk. As a general property of the field configuration generated by the galactic dynamo, the field lines show a more tightly wound appearance in the outer region of the disk, in spite of the decrease of shear strength in the galactic rotation.
Chiba Masashi
Tosa Makoto
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