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

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Hill, AS, Landecker, TL, Carretti, E, Douglas, K, Sun, XH, Gaensler, BM, Mao, SA, McClure-Griffiths, NM, Reich, W, Wolleben, M, Dickey, JM ORCID: 0000-0002-6300-7459, Gray, AD, Haverkorn, M, Leahy, JP and Schnitzeler, DHFM 2017 , 'The Fan Region at 1.5 GHz - I. Polarized synchrotron emission extending beyond the Perseus Arm' , Monthly Notices of the Royal Astronomical Society, vol. 467, no. 4 , pp. 4631-4646 , doi: 10.1093/mnras/stx389.

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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 1.3–1.8 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 Type: Article
Authors/Creators: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
Keywords: polarization, ISM: magnetic fields, ISM: structure, galaxy: structure, radio continuum: ISM
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Blackwell Publishing Ltd
ISSN: 0035-8711
DOI / ID Number: 10.1093/mnras/stx389
Copyright Information:

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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