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Open AccessArticle

Magnetic-Field Vector Maps of Nearby Spiral Galaxies

Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan
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Galaxies 2019, 7(1), 32; https://doi.org/10.3390/galaxies7010032
Received: 19 December 2018 / Revised: 1 February 2019 / Accepted: 5 February 2019 / Published: 11 February 2019
(This article belongs to the Special Issue The Power of Faraday Tomography)
We present a method for determining the directions of magnetic-field vectors in a spiral galaxy using two synchrotron polarization maps, an optical image, and a velocity field. The orientation of the transverse magnetic field is determined with a synchrotron polarization map of a higher-frequency band, and the 180°-ambiguity is solved by using a sign of Rotation Measure (RM) after determining the geometrical orientation of a disk based on an assumption of trailing spiral arms. The advantage of this method is that the direction of a magnetic vector for each line of sight throughout the galaxy can inexpensively be determined, with easily available data and simple assumptions. We applied this method to three nearby spiral galaxies using archival data obtained with a Very Large Array (VLA) to demonstrate how it works. The three galaxies have both clockwise and counterclockwise magnetic fields, which implies that none of the three galaxies is classified in a simple Axis-Symmetric type, but types of higher modes, and that magnetic reversals commonly exist. View Full-Text
Keywords: ISM: magnetic fields; galaxies: spiral; galaxies: magnetic fields; radio continuum: ISM; methods: data analysis ISM: magnetic fields; galaxies: spiral; galaxies: magnetic fields; radio continuum: ISM; methods: data analysis
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Nakanishi, H.; Kurahara, K.; Anraku, K. Magnetic-Field Vector Maps of Nearby Spiral Galaxies. Galaxies 2019, 7, 32.

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