J/A+A/687/A23 Faraday tomography of LoTSS-DR2 - outer Galaxy (Erceg+ 2024)
Faraday tomography of LoTSS-DR2 data.
II. Multi-tracer analysis in the high-latitude outer Galaxy.
Erceg A., Jelic V., Haverkorn M., Bracco A., Ceraj L., Turic L., Soler J.D.
<Astron. Astrophys. 687, A23 (2024)>
=2024A&A...687A..23E 2024A&A...687A..23E (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Magnetic fields ; Polarization ;
Radio continuum
Keywords: magnetic fields - polarisation - ISM: general - ISM: magnetic fields -
ISM: structure - radio continuum: ISM
Abstract:
We conducted a follow-up study on the analysis of the LOw Frequency
ARray (LOFAR) Two-metre Sky Survey (LoTSS) mosaic in the high-latitude
outer Galaxy presented in the first paper of this series. Here, we
focus on the search for alignment between the magnetic field traced by
dust, HI filaments, starlight optical linear polarisation, and linear
depolarised structures (depolarisation canals) observed in
low-frequency synchrotron polarisation. This alignment was previously
found in several smaller fields observed with LOFAR, offering valuable
insights into the nature of the interstellar medium and the 3D spatial
distribution of the diffuse ionised medium.
We aim to determine whether the alignment of the interstellar medium
(ISM) phases observed through multiple tracers is a common occurrence
or an exception. Additionally, in areas where depolarisation canals
align with the magnetic field, we use starlight polarisation to
constrain the distance to the structures associated with the observed
canals.
We employed the Rolling Hough Transform (RHT) and projected Rayleigh
statistics (PRS) to identify and quantify the alignment between the
different tracers. We used these tools to detect linear features in
the data and quantify the significance of the orientation trends
between pairs of tracers.
On the scale of the whole mosaic, we did not find any evidence of a
universal alignment among the three tracers. However, in one
particular area, the western region (Dec between 29 degrees and
70° and RA between 7h44m and 9h20m), we do find a significant
alignment between the magnetic field, depolarisation canals, and HI
filaments. Based on this alignment, we used the starlight polarisation
of stars with known parallax distances to estimate that the minimum
distance to the structures observed by LOFAR in this region lies
within the range of 200 to 240pc. We associate these structures with
the edge of the Local Bubble.
Description:
The maximum polarised intensity image synthesised from a Faraday depth
cube of the LoTSS-DR2 outer Galaxy observations. The image covers
around 3100 square degrees, centred around 12h45m +44 degrees. Angular
resolution of this dataset is 5.5 arcmin. The maximum polarised
intensity image was created by taking the highest intensity in each
spectrum in the Faraday cube. We searched for a peak in the range from
-50 to 50rad/m2. Faraday resolution of the used cube to derive this
data is 1rad/m2 and the cube can be found at:
https://data.fulir.irb.hr/islandora/object/irb:367 .
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 75 1 Information of fits file
fits/* . 1 fits file
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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 center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 35 I6 Kibyte size Size of FITS file
37- 47 A11 --- FileName Name of FITS file, in subdirectory fits
49- 75 A27 --- Title Title of the FITS file (1)
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Note (1): Intensity is given in units of Jy/PSF/RMSF, where PSF is Point Spread
Function and RMSF is Rotation Measure Spread Function.
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Acknowledgements:
Ana Erceg, aerceg(at)irb.hr
Vibor Jelic, vibor(at)irb.hr
References:
Erceg et al., Paper I 2022A&A...663A...7E 2022A&A...663A...7E
(End) Patricia Vannier [CDS] 07-May-2024