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A Survey of Extragalactic Faraday Rotation at High Galactic Latitute: the Vertical Magnetic Field of the Milky Way Toward the Galactic Poles

Lookup NU author(s): Professor Anvar ShukurovORCiD

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Abstract

We present a study of the vertical magnetic field of the Milky Way toward the Galactic poles, determined from observations of Faraday rotation toward more than 1000 polarized extragalactic radio sources at Galactic latitudes vertical bar b vertical bar >= 77 degrees, using the Westerbork Radio Synthesis Telescope and the Australia Telescope Compact Array. We find median rotation measures (RMs) of 0.0 +/- 0.5 rad m(-2) and +6.3 +/- 0.7 rad m(-2) 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 Galactic magnetic field. The angular fluctuations in RM seen in our data show no preferred scale within the range approximate to 0 degrees.1 to approximate to 25 degrees. The observed standard deviation in RM of similar to 9 rad m(-2) then implies an upper limit of similar to 1 mu G on the strength of the random magnetic field in the warm ionized medium at high Galactic latitudes.

Publication metadata

Author(s): Mao SA, Gaensler BM, Haverkorn M, Zweibel EG, Madsen GJ, McClure-Griffiths NM, Shukurov A, Kronberg PP

Publication type: Article

Publication status: Published

Journal: Astrophysical Journal

Year: 2010

Volume: 714

Issue: 2

Pages: 1170-1186

Print publication date: 01/05/2010

ISSN (print): 0004-637X

ISSN (electronic): 1538-4357

Publisher: Institute of Physics Publishing, Inc.

URL: http://dx.doi.org/10.1088/0004-637X/714/2/1170

DOI: 10.1088/0004-637X/714/2/1170

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