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

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° < 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.

Accepted to MNRAS

References in corpus (13)

• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
• Radio observational constraints on Galactic 3D-emission models
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• Magnetism in the spiral galaxy NGC 6946: magnetic arms, depolarization rings, dynamo modes and helical fields
• Separation of anomalous and synchrotron emissions using WMAP polarization data
• Dark matter in the Milky Way, II. the HI gas distribution as a tracer of the gravitational potential
• A Sino-German lambda6 cm polarization survey of the Galactic plane I. Survey strategy and results for the first survey region
• Antisymmetry in the Faraday Rotation Sky Caused by a Nearby Magnetized Bubble
• The Fragmenting Superbubble Associated with the HII Region W4
• Gain and Polarization Properties of a Large Radio Telescope from Calculation and Measurement: The John A. Galt Telescope
• Magnetic fields of the W4 superbubble

Cited by in corpus (8)

• The Galactic Magneto-Ionic Medium Survey: Moments of the Faraday Spectra
• Practical Modeling of Large-Scale Galactic Magnetic Fields: Status and Prospects
• Diffuse polarized emission in the LOFAR Two-meter Sky Survey
• The Global Magneto-Ionic Medium Survey: Polarimetry of the Southern Sky from 300 to 480 MHz
• Through thick or thin: Multiple components of the magneto-ionic medium towards the nearby $\mathrm{H}\mathrm{II}$ region Sharpless 2-27 revealed by Faraday tomography
• The Global Magneto-Ionic Medium Survey: A Faraday Depth Survey of the Northern Sky Covering 1280-1750 MHz
• HI anisotropies associated with radio-polarimetric filaments. Steep power spectra associated with cold gas
• Advanced Diagnostics for the Study of Linearly Polarized Emission. I: Derivation