Next Article in Journal
Centaurus A: Hard X-ray and High-Energy Gamma-Ray Light Curve Correlation
Next Article in Special Issue
Revisiting the Equipartition Assumption in Star-Forming Galaxies
Previous Article in Journal
CHANG-ES: XVIII—The CHANG-ES Survey and Selected Results
Previous Article in Special Issue
Magnetic Fields Around Galactic Discs
Open AccessArticle

Faraday Rotation of Extended Emission as a Probe of the Large-Scale Galactic Magnetic Field

1
Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada
2
Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
3
Dominion Radio Astrophysical Observatory, Herzberg Astronomy and Astrophysics Research Centre, National Research Council Canada, P.O. Box 248, Penticton, BC V2A 6J9, Canada
*
Authors to whom correspondence should be addressed.
Galaxies 2019, 7(2), 43; https://doi.org/10.3390/galaxies7020043
Received: 30 January 2019 / Revised: 14 March 2019 / Accepted: 22 March 2019 / Published: 27 March 2019
(This article belongs to the Special Issue New Perspectives on Galactic Magnetism)
The Galactic magnetic field is an integral constituent of the interstellar medium (ISM), and knowledge of its structure is crucial to understanding Galactic dynamics. The Rotation Measures (RM) of extragalactic (EG) sources have been the basis of comprehensive Galactic magnetic field models. Polarised extended emission (XE) is also seen along lines of sight through the Galactic disk, and also displays the effects of Faraday rotation. Our aim is to investigate and understand the relationship between EG and XE RMs near the Galactic plane, and to determine how the XE RMs, a hitherto unused resource, can be used as a probe of the large-scale Galactic magnetic field. We used polarisation data from the Canadian Galactic Plane Survey (CGPS), observed near 1420 MHz with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. We calculated RMs from a linear fit to the polarisation angles as a function of wavelength squared in four frequency channels, for both the EG sources and the XE. Across the CGPS area, 55 < < 193 , 3 < b < 5 , the RMs of the XE closely track the RMs of the EG sources, with XE RMs about half the value of EG-source RMs. The exceptions are places where large local HII complexes heavily depolarise more distant emission. We conclude that there is valuable information in the XE RM dataset. The factor of 2 between the two types of RM values is close to that expected from a Burn slab model of the ISM. This result indicates that, at least in the outer Galaxy, the EG and XE sources are likely probing similar depths, and that the Faraday rotating medium and the synchrotron emitting medium have similar variation with galactocentric distance. View Full-Text
Keywords: galaxy: structure; ISM: magnetic fields; polarization; radio continuum: ISM; techniques: interferometric galaxy: structure; ISM: magnetic fields; polarization; radio continuum: ISM; techniques: interferometric
Show Figures

Figure 1

MDPI and ACS Style

Ordog, A.; Booth, R.A.; Van Eck, C.L.; Brown, J.-A.C.; Landecker, T.L. Faraday Rotation of Extended Emission as a Probe of the Large-Scale Galactic Magnetic Field. Galaxies 2019, 7, 43.

Show more citation formats Show less citations formats
Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Access Map by Country/Region

1
Back to TopTop