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| Paper: |
Magnetic Fields in Spiral Arms and Bars |
| Volume: |
275, Disks of Galaxies: Kinematics, Dynamics and Perturbations |
| Page: |
331 |
| Authors: |
Beck, R. |
| Abstract: |
Radio polarization maps of about 70 spiral, barred and irregular galaxies have been observed with the Effelsberg, Parkes, VLA and ATCA telescopes. Interstellar magnetic fields with a well-ordered spiral structure exist in grand-design, flocculent and even irregular galaxies. In grand-design galaxies the fields are aligned parallel to the optical spiral arms, but the strongest regular fields (~=10 μG) are found between the optical arms, sometimes forming ``magnetic spiral arms''. Within the optical spiral arms, the total field is strong (typically 20 μG), but irregular. Processes related to star formation enhance and tangle the fields so that little polarization is observed. Faraday rotation patterns support the existence of coherent large-scale fields in galactic disks generated by dynamos. In the majority of galaxies a superposition of several dynamo modes is required. Magnetic fields in strongly barred galaxies are mostly aligned with the gas flow around the bar, except for the upstream region where the regular field is enhanced and bends towards the bar. Within (and interior to) the circumnuclear ring the field is of spiral shape, which leads to magnetic stress, possibly driving gas inflow to the nucleus. Present-day radio polarization observations are limited by sensitivity. Next-generation radio telescopes (e.g. the Square Kilometer Array) will be able to reveal the full wealth of magnetic structures in galaxies. |
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