J/A+A/674/A119 LoTTS Deep Fields ELAIS-N1 (Snidaric+, 2023)
LOFAR Deep Fields: Probing faint Galactic polarized emission in ELAIS-N1.
Snidaric I., Jelic V., Mevius M., Brentjens M., Erceg A., Shimwell T.W.,
Piras S., Horellou C., Sabater J., Best P.N., Bracco A., Ceraj L.,
Haverkorn M., O'Sullivan S.P., Turic L., Vacca V.
<Astron. Astrophys. 674, A119 (2023)>
=2023A&A...674A.119S 2023A&A...674A.119S (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Polarization ; Radio continuum
Keywords: ISM: general - ISM: structure - ISM: magnetic fields -
radio continuum: ISM - techniques: interferometric -
techniques: polarimetric
Abstract:
We present the first deep polarimetric study of Galactic synchrotron
emission at low radio frequencies. Our study is based on 21
observations of the European Large Area Infrared Space Observatory
Survey-North 1 (ELAIS-N1) field using the Low-Frequency Array (LOFAR)
at frequencies from 114.9 to 177.4MHz. These data are a part of the
LOFAR Two-metre Sky Survey (LoTTS) Deep Fields Data Release 1. We used
very low-resolution (4.3') Stokes QU data cubes of this release. We
applied rotation measure (RM) synthesis to decompose the distribution
of polarised structures in Faraday depth, and cross-correlation RM
synthesis to align different observations in Faraday depth. We stacked
images of about 150 hours of the ELAIS-N1 observations to produce the
deepest Faraday cube at low radio frequencies to date, tailored to
studies of Galactic synchrotron emission and the intervening
magneto-ionic interstellar medium. This Faraday cube covers 36 deg2
of the sky and has a noise of 27uJy/PSF/RMSF in polarised intensity.
This is an improvement in noise by a factor of approximately the
square root of the number of stacked data cubes (sqrt(20)), as
expected, compared to the one in a single data cube based on
five-to-eight-hour observations. We detect a faint component of
diffuse polarised emission in the stacked cube, which was not detected
previously. Additionally, we verify the reliability of the ionospheric
Faraday rotation corrections estimated from the satellite-based total
electron content measurements to be of 0.05rad/m2. We also
demonstrate that diffuse polarised emission itself can be used to
account for the relative ionospheric Faraday rotation corrections with
respect to a reference observation.
Description:
The stacked Faraday cube based on 20 ELAIS-N1 LoTTS-Deep Fields
observations, 150 hours of data in total, taken under project codes
LC0_019, LC2_024 and LC4_008. The cube is given in polarized intensity
in units of Jansky/PSF/RMSF as a function of RA, Dec, and Faraday
depth. The cube covers a Faraday depth range from -50 to +50rad/m2
in 0.25rad/m2 steps. The resolution in Faraday depth is 0.9rad/m2.
The largest measured scale in Faraday depth is 1.1m-2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 70 1 Informations of Faraday cube
fits/* . 1 Faraday cube
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See also:
J/MNRAS/371/1891 : GOODS ELAIS-N1 24um flux densities (Rodighiero+, 2006)
J/ApJ/666/201 : Radio polarimetry of the ELAIS N1 field (Taylor+, 2007)
J/MNRAS/383/75 : Deep 610MHz survey of ELAIS-N1 sources (Garn+, 2008)
J/MNRAS/395/269 : ELAIS-N1 field 325MHz observations (Sirothia+, 2009)
J/MNRAS/472/4259 : IRAC Dark Field, ELAIS-N1 & ADF-S galaxies (Davidge+, 2017)
J/MNRAS/490/243 : ELAIS N1 field uGMRT 400MHz source catalog
(Chakraborty+, 2020)
J/A+A/648/A2 : LOFAR Two-metre Sky Survey Deep Fields DR1 (Sabater+, 2021)
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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 30 I3 --- Nz Number of slices
32- 41 A10 "datime" Obs.date Observation date
43- 48 I6 Kibyte size Size of FITS file
50- 57 A8 --- FileName Name of FITS file, in subdirectory fits
59- 70 A12 --- Title Title of the FITS file
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Acknowledgements:
Iva Snidaric, isnidar(at)irb.hr
(End) Patricia Vannier [CDS] 04-Apr-2023