Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21721703m&link_type=abstract
American Astronomical Society, AAS Meeting #217, #217.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Coherent large scale magnetic fields exist in galaxies, yet their origin remains unclear. We present studies of the magnetic field structure in the Milky Way and in the Large Magellanic Cloud to shed new light on the field generation mechanism. We use the powerful Faraday rotation effect, which allows the determination of both the field direction and its strength, as the magnetic field probe. We measure the vertical magnetic field of the Milky Way toward the Galactic poles from observations of Faraday rotation toward more than 1000 polarized extragalactic radio sources at Galactic latitudes |b|>77°, using the Westerbork Radio Synthesis Telescope and the Australia Telescope Compact Array. We find median rotation measures (RMs) of 0.0 ± 0.5 rad/m2 and +6.3 ± 0.7 rad/m2 toward the north and south Galactic poles respectively, demonstrating that there is no coherent vertical magnetic field in the Milky Way at the Sun's position. If this is a global property of the Milky Way's magnetism, then the lack of symmetry across the disk rules out pure dipole or quadrupole geometries for the Milky Way magnetic field. The observed RM distribution can be explained by a disk and a halo dynamo of different parities operating simultaneously in the Galaxy. The proximity of the Large Magellanic Cloud allows a detailed study of its magnetic field structure. We have mapped the LMC's diffuse synchrotron polarization at 1.4 GHz using the Parkes Radio telescope. We present a magnetic field model of the LMC that can explain both the RMs of the diffuse polarized emission and those of the background extragalactic sources simultaneously.
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