J/other/Galax/7.43 Faraday rotation of extended emission (Ordog+, 2019)
Faraday rotation of extended emission as a probe of the large-scale Galactic
magnetic field.
Ordog A., Booth R.A., Van Eck C.L., Brown J.-A.C., Landecker T.L.
<Galaxies, vol. 7, 43 (2019)>
=2019Galax...7...43O 2019Galax...7...43O (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Polarization ; Magnetic fields
Keywords: galaxy: structure - ISM: magnetic fields - polarization -
radio continuum: ISM - techniques: interferometric
Abstract:
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, l=55 to l=193 degrees, b=-3 to b=5
degrees, 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.
Description:
The Rotation Measure (RM) map we present here was calculated using
Stokes Q and U data from the Canadian Galactic Plane Survey
polarisation dataset. The data were observed using the Dominion Radio
Astrophysical Observatory Synthesis Telescope as part of the CGPS, in
4 frequency channels centred at 1407.2, 1414.1, 1427.7 and 1436.6MHz.
We calculated RMs for the extended emission assuming a linear fit to
polarisation angle as a function of wavelength squared. We then
applied a filtering process as described in the paper. The size of the
pixels in the map is 0.005 degrees by 0.005 degrees, and the entire
map is 1825 by 29025 pixels, covering the CGPS longitude and latitude
range.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 70 1 Information on fits image
fits/* . 1 Fits imag
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See also:
VI/128 : Log of CGPS exposures (Taylor+, 2003-)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1 A1 --- --- [G]
2- 10 F9.5 deg GLON Galactic longitude of center (J2000)
11- 19 F9.5 deg GLAT Galactic latitude of center (J2000)
21- 25 I5 --- Nx Number of pixels along X-axis
27- 30 I4 --- Ny Number of pixels along Y-axis
32- 37 I6 Kibyte size Size of FITS file
39- 50 A12 --- FileName Name of FITS file, in subdirectory fits
52- 70 A19 --- Title Title of the FITS file
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Acknowledgements:
Anna Ordog, aordog(at)ucalgary.ca
(End) Patricia Vannier [CDS] 29-Mar-2019