J/A+A/654/A5 Faraday cubes Fields A B and C (Turic+, 2021)
Multi-tracer analysis of straight depolarisation canals in the surroundings of
the 3C 196 field.
Turic L., Jelic V., Jaspers R., Haverkorn M., Bracco A., Erceg A., Ceraj L.,
van Eck C., Zaroubi S.
<Astron. Astrophys. 654, A5 (2021)>
=2021A&A...654A...5T 2021A&A...654A...5T (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Polarization ; Radio continuum
Keywords: ISM: general - ISM: magnetic fields - ISM: structure -
radio continuum: ISM - techniques: interferometric -
techniques: polarimetric
Abstract:
Faraday tomography of a field centred on the extragalactic point
source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an
intertwined structure of diffuse polarised emission with straight
depolarisation canals and tracers of the magnetized and multi-phase
interstellar medium (ISM), such as dust and line emission from atomic
hydrogen (HI). This study aims at extending the multi-tracer analysis
of LOFAR data to three additional fields in the surroundings of the 3C
196 field. For the first time, we study the three-dimensional
structure of the LOFAR emission by determining the distance to the
depolarisation canals. We use the Rolling Hough Transform to compare
the orientation of the depolarisation canals with that of the
filamentary structure seen in HI and, based on starlight and dust
polarisation data, with that of the plane-of-the-sky magnetic field.
Stellar parallaxes from Gaia complement the starlight polarisation
with the corresponding distances.
Faraday tomography of the three fields shows a rich network of diffuse
polarised emission at Faraday depths between -10rad/m2 and
+15rad/m2. A complex system of straight depolarisation canals
resembles that of the 3C 196 field. The depolarisation canals align
both with the HI filaments and with the magnetic field probed by dust.
The observed alignment suggests that an ordered magnetic field
organises the multiphase ISM over a large area (∼20°). In one
field, two groups of stars at distances below and above 200pc,
respectively, show distinct magnetic-field orientations. These are
both comparable with the orientations of the depolarisation canals in
the same field. We conclude that the depolarisation canals likely
trace the same change of the magnetic field as probed by the stars,
which corresponds to the edge of the Local Bubble.
Description:
The Faraday depth cubes of three fields located nearby the 3C 196
field. Field A is located 10° below the 3C 196 field, towards the
Galactic plane; Field B is at similar Galactic latitude as the 3C 196
field, but 10° towards larger Galactic longitudes; and Field C is
in the coldest part of the North Galactic halo. The cubes are given in
polarized intensity as a function of RA, Dec, and Faraday depth,
synthesized from the LOw Frequency ARray (LOFAR) High Band Antennas
(HBA) observations (Observational IDs: L428654, L431160 and L431596,
taken under project code LC5_008).
The cubes cover a Faraday depth range from -25rad/m2 to +25rad/m2
in 0.25rad/m2 steps, given in units of Jansky/PSF/RMSF. PSF is is
Point Spread Function (3.9x3.6arcmin) and RMSF is Rotation Measure
Spread Function (1.8rad/m2). The largest measured scale in Faraday
depth is 0.8rad/m2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 71 3 List of fits datacubes
fits/* . 3 Individual fits datacubes
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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)
10- 18 F9.5 deg DEdeg Declination of image centre (J2000)
20- 23 I4 --- Nx Number of pixels in along X-axis
25- 28 I4 --- Ny Number of pixels in along Y-axis
30- 32 I3 --- Nz Number of pixels in Faraday depth
34- 40 I7 Kibyte size Size of FITS file
42- 50 A9 --- FileName Name of the fits file in subdirectory fits
52- 71 A20 --- Title Title of the fits file
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Acknowledgements:
Luka Turic, lturic(at)irb.hr
(End) Patricia Vannier [CDS] 25-Aug-2021