J/A+A/623/A71 LOTSS HETDEX Faraday depth cube (Van Eck+, 2019)
Diffuse polarized emission in the LOFAR Two-meter Sky Survey.
Van Eck C.L., Haverkorn M., Alves M.I.R., Beck R., Best P., Carretti E.,
Chyzy K., Ensslin T., Farnes J.S., Ferriere K., Heald G., Iacobelli M.,
Jelic V., Reich W., Rottgering H.J.A., Schnitzeler D.H.F.M.
<Astron. Astrophys. 623, A71 (2019)>
=2019A&A...623A..71V 2019A&A...623A..71V (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Polarization ; Radio continuum
Keywords: ISM: magnetic fields - polarization
Abstract:
Faraday tomography allows us to map diffuse polarized synchrotron
emission from our Galaxy and use it to interpret the magnetic field in
the interstellar medium (ISM). We have applied Faraday tomography to
60 observations from the LOFAR Two-Meter Sky Survey (LOTSS) and
produced a Faraday depth cube mosaic covering 568 square degrees at
high Galactic latitudes, at 4.3 angular resolution and 1rad/m2
Faraday depth resolution, with a typical noise level of 50-100uJy per
point spread function (PSF) per rotation measure spread function
(RMSF) (40-80mK/RMSF). While parts of the images are strongly
affected by instrumental polarization, we observe diffuse polarized
emission throughout most of the field, with typical brightness between
1 and 6K/RMSF, and Faraday depths between -7 and +25rad/m2.
We observe many new polarization features, some up to 15deg in length.
These include two regions with very uniformly structured, linear
gradients in the Faraday depth; we measured the steepness of these
gradients as 2.6 and 13rad/m2/deg. We also observe a relationship
between one of the gradients and an HI filament in the local ISM.
Other ISM tracers were also checked for correlations with our
polarization data and none were found, but very little signal was seen
in most tracers in this region. We conclude that the LOTSS data are
very well suited for Faraday tomography, and that a full-scale survey
with all the LOTSS data has the potential to reveal many new Galactic
polarization features and map out diffuse Faraday depth structure
across the entire northern hemisphere.
Description:
The Faraday depth cube of the LOTSS HETDEX Spring field, showing
polarized Intensity as a function of RA, Dec, and Faraday depth. The
region covered is 11-15h RA and 45-57deg Dec, with 4.3arcmin
resolution, and from -25 to +25rad/m2 in Faraday depth in steps of
0.25rad/m2. The Faraday depth resolution is 0.9rad/m2, and the
largest measured scale in Faraday depth is 1rad/m2.
The RM cube is given in units of Jansky/PSF/RMSF, where PSF is Point
Spread Function (4.3-arcmin) and RMSF is Rotation Measure Spread
Function (1rad/m2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 68 1 List of properties of the data cube
fits/* . 1 Faraday depth cube
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right ascension of image centre (J2000)
11- 19 F9.6 deg DEdeg Declination of image centre (J2000)
21- 22 I2 arcsec/pix Scale Pixel scale
24- 27 I4 --- Nx Number of pixels in along X-axis
29- 32 I4 --- Ny Number of pixels in along Y-axis
34- 36 I3 --- Nz Number of pixels in Faraday depth
38- 49 A12 --- FileName Name of the fits file in subdirectory fits
51- 68 A18 --- Title Title of the fits file
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Acknowledgements:
Cameron Van Eck, cameron.van.eck(at)dunlap.utoronto.ca
(End) Patricia Vannier [CDS] 30-Jan-2019