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The Fan Region at 1.5 GHz - I. Polarized synchrotron emission extending beyond the Perseus Arm

Citation

Hill, AS and Landecker, TL and Carretti, E and Douglas, K and Sun, XH and Gaensler, BM and Mao, SA and McClure-Griffiths, NM and Reich, W and Wolleben, M and Dickey, JM and Gray, AD and Haverkorn, M and Leahy, JP and Schnitzeler, DHFM, The Fan Region at 1.5 GHz - I. Polarized synchrotron emission extending beyond the Perseus Arm, Monthly Notices of the Royal Astronomical Society, 467, (4) pp. 4631-4646. ISSN 0035-8711 (2017) [Refereed Article]


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DOI: doi:10.1093/mnras/stx389

Abstract

The Fan Region is one of the dominant features in the polarized radio sky, long thought to be a local (distance ≲500  pc) synchrotron feature. We present 1.31.8 GHz polarized radio continuum observations of the region from the Global Magneto-Ionic Medium Survey and compare them to maps of Hα and polarized radio continuum intensity from 0.408 to 353 GHz. The high-frequency (>1 GHz) and low-frequency (≲600 MHz) emissions have different morphologies, suggesting a different physical origin. Portions of the 1.5 GHz Fan Region emission are depolarized by ≈30 per cent by ionized gas structures in the Perseus Arm, indicating that this fraction of the emission originates ≳2 kpc away. We argue for the same conclusion based on the high polarization fraction at 1.5 GHz (≈40 per cent). The Fan Region is offset with respect to the Galactic plane, covering −5 ≲ b ≲ +10; we attribute this offset to the warp in the outer Galaxy. We discuss origins of the polarized emission, including the spiral Galactic magnetic field. This idea is a plausible contributing factor although no model to date readily reproduces all of the observations. We conclude that models of the Galactic magnetic field should account for the ≳1  GHz emission from the Fan Region as a Galactic scale, not purely local, feature.

Item Details

Item Type:Refereed Article
Keywords:polarization, ISM: magnetic fields, ISM: structure, galaxy: structure, radio continuum: ISM
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Galactic Astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Dickey, JM (Professor John Dickey)
ID Code:122643
Year Published:2017
Funding Support:Australian Research Council (DP110104101)
Web of Science® Times Cited:2
Deposited By:Office of the School of Physical Sciences
Deposited On:2017-11-21
Last Modified:2017-11-22
Downloads:0

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