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New constraints on the galactic halo magnetic field using rotation measures of extragalactic sources toward the outer galaxy

Lookup NU author(s): Professor Anvar Shukurov

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Abstract

We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) toward 641 polarized extragalactic radio sources in the Galactic longitude range 100 degrees-117 degrees, within 30 degrees of the Galactic plane. For vertical bar b vertical bar < 15 degrees, we observe a symmetric RM distribution about the Galactic plane. This is consistent with a disk field in the Perseus arm of even parity across the Galactic mid-plane. In the range 15 degrees < vertical bar b vertical bar < 30 degrees, we find median RMs of -15 +/- 4 rad m(-2) and -62 +/- 5 rad m(-2) in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, then this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RMas a function of Galactic latitude in this longitude range is such that RMs become more negative at larger vertical bar b vertical bar. This is consistent with an azimuthal magnetic field of strength 2 mu G (7 mu G) at a height 0.8-2 kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.


Publication metadata

Author(s): Mao SA, McClure-Griffiths NM, Gaensler BM, Brown JC, van Eck CL, Haverkorn M, Kronberg PP, Stil JM, Shukurov A, Taylor AR

Publication type: Article

Publication status: Published

Journal: Astrophysical Journal

Year: 2012

Volume: 755

Issue: 1

Pages: 21

Print publication date: 23/07/2012

ISSN (print): 0004-637X

ISSN (electronic): 1538-4357

Publisher: Institute of Physics Publishing, Inc.

URL: http://dx.doi.org/10.1088/0004-637X/755/1/21

DOI: 10.1088/0004-637X/755/1/21


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