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arXiv · 1702.02200

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

A. S. Hill·T. L. Landecker·E. Carretti·K. Douglas·X. H. Sun·B. M. Gaensler·S. A. Mao·N. M. McClure-Griffiths·W. Reich·M. Wolleben·J. M. Dickey·A. D. Gray·M. Haverkorn·J. P. Leahy·D. H. F. M. Schnitzeler
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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 (GMIMS) and compare them to maps of Halpha and polarized radio continuum intensity from 0.408-353 GHz. The high-frequency (> 1 GHz) and low-frequency (< 600 MHz) emission have different morphologies, suggesting a different physical origin. Portions of the 1.5 GHz Fan Region emission are depolarized by about 30% 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 (about 40%). The Fan Region is offset with respect to the Galactic plane, covering -5{\deg} < b < +10{\deg}; 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.

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A. S. Hill, T. L. Landecker, E. Carretti, K. Douglas, X. H. Sun, B. M. Gaensler, S. A. Mao, N. M. McClure-Griffiths, W. Reich, M. Wolleben, J. M. Dickey, A. D. Gray, M. Haverkorn, J. P. Leahy, D. H. F. M. Schnitzeler. 2017-02-07. The Fan Region at 1.5 GHz. I: Polarized synchrotron emission extending beyond the Perseus Arm. https://doi.org/10.1093/mnras/stx389

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