J/A+A/673/A165 LOFAR LBA Sky Survey First Release (de Gasperin+, 2023)
The LOFAR LBA Sky Survey. II. First data release.
de Gasperin F., Edler H., Williams W.L., Callingham J.R., Asabere B.,
Bruggen M., Brunetti G., Dijkema T.J., Hardcastle M.J., Iacobelli M.,
Offringa A., Norden M.J., Rottgering H., Shimwell T., van Weeren R.,
Tasse C., Bomans D.J., Bonafede A., Botteon A., Cassano R., Chyzy K.T.,
Cuciti V., Emig K.L., Kadler M., Miley G., Mingo B., Oei M.S.S.L.,
Prandoni I., Schwarz D.J., Zarka P.
<Astron. Astrophys. 673, A165 (2023)>
=2023A&A...673A.165D 2023A&A...673A.165D (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio continuum
Keywords: surveys - catalogs - radio continuum: general -
techniques: image processing
Abstract:
The Low Frequency Array (LOFAR) is the only existing radio
interferometer able to observe at ultra-low frequencies (<100MHz) with
high resolution (<15-arcsec) and high sensitivity (<1mJy/beam). To
exploit these capabilities, the LOFAR Surveys Key Science Project is
using the LOFAR Low Band Antenna (LBA) to carry out a sensitive
wide-area survey at 41-66MHz named the LOFAR LBA Sky Survey (LoLSS).
LoLSS is covering the whole northern sky above declination 24 deg with
a resolution of 15-arcsec and a sensitivity of 1-2mJy/beam (1 σ)
depending on declination, field properties, and observing conditions.
Here we present the first data release, including a discussion of the
calibration strategy and the properties of the released images and
catalogues. A fully automated pipeline was used to reduce the 95
fields included in this data release. The data reduction procedures
developed for this project have a general application and are
currently being used to process almost all LOFAR LBA interferometric
observations. Compared to the preliminary release, direction-dependent
errors have been derived and corrected for during the calibration
process. This results in a typical sensitivity of 1.55mJy/beam, which
is four times better than for the preliminary release, at the target
resolution of 15 arcsec. The first data release of the LOFAR LBA Sky
Survey covers 650 sqdeg in the HETDEX spring field. The resultant data
products released to the community include mosaic images (I and V
Stokes) of the region, and a catalogue of 42463 detected sources and
related Gaussian components used to describe the sources'
morphologies. Separate catalogues for the six in-band frequencies of
44, 48, 52, 56, 60, and 64MHz are also released. The first data
release of LoLSS shows that, despite the influences of the ionosphere
and radio frequency interference, LOFAR can conduct large-scale
surveys in the frequency window 42-66MHz with unprecedentedly high
sensitivity and resolution. The data can be used to derive unique
information on the low-frequency spectral properties of many thousands
of sources with a wide range of applications in extragalactic and
galactic astronomy.
Description:
First release of the LOFAR LBA Sky Survey. The catalogue contains
42463 radio sources detected in the HETDEX Spring field at 54MHz. The
survey has a median sensitivity of 1.55mJy/beam with an angular
resolution of 15 arcsec.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
lolss1s.dat 317 42463 LoLSS DR1 v1.1 catalogue (LoLSSDR1v1.1.srl)
lolss1g.dat 339 53377 LoLSS DR1 v1.1 catalogue with Gaussians
(LoLSSDR1v1.1.gaus)
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See also:
J/A+A/659/A1 : LOFAR Two-metre Sky Survey (LoTSS) DR2 (Shimwell+, 2022)
http://www.lofar-surveys.org : LoLSS Home Page
Byte-by-byte Description of file: lolss1s.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Source The source ID (LOL1JHHMMSS.s+DDMMSS) (G1)
22- 39 F18.14 deg RAdeg Centroid right ascension (J2000)
41- 53 F13.10 arcsec e_RAdeg Uncertainty on right ascension (1 sigma)
55- 72 F18.15 deg DEdeg Centroid declination (J2000)
74- 85 F12.10 arcsec e_DEdeg Uncertainty on declination (1 sigma)
87-100 F14.7 mJy Ftot Integrated flux density at 54MHz
102-112 F11.7 mJy e_Ftot Uncertainty on flux density at 54MHz
(1 sigma)
114-127 F14.7 mJy/beam Fpeak Peak brightness at 54MHz
129-139 F11.8 mJy/beam e_Fpeak Uncertainty on peak brightness at 54MHz
(1 sigma)
141-151 F11.7 arcsec Maj Major axis
153-164 F12.9 arcsec e_Maj Uncertainty on major axis (1 sigma)
166-175 F10.7 arcsec Min Minor axis
177-188 F12.10 arcsec E_Min Uncertainty on minor axis (1 sigma)
190-202 F13.9 deg PA Position angle
204-216 F13.9 deg e_PA Uncertainty on position angle (1 sigma)
218-228 F11.7 arcsec DCMaj Deconvolved Major axis
230-241 F12.9 arcsec e_DCMaj Uncertainty on deconvolved major axis
(1 sigma)
243-254 F12.9 arcsec DCMin Deconvolved Minor axis
256-267 F12.10 arcsec e_DCMin Uncertainty on deconvolved minor axis
(1 sigma)
269-281 F13.9 deg DCPA Deconvolved position angle
283-295 F13.9 deg e_DCPA Uncertainty on deconvolved position angle
(1 sigma)
297-307 F11.8 mJy/beam Islrms Local rms noise at the source location
309 A1 --- SCode [CMS] Source code (G2)
311-317 A7 --- Mosaic Mosaic identifier (G3)
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Byte-by-byte Description of file: lolss1g.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Source The source ID (LOL1JHHMMSS.s+DDMMSS) (G1)
22- 25 I4 --- GausId Gaussian identifier
27- 44 F18.14 deg RAdeg Centroid right ascension (J2000)
46- 59 E14.6 arcsec e_RAdeg Uncertainty on right ascension (1 sigma)
61- 78 F18.15 deg DEdeg Centroid declination (J2000)
80- 91 F12.10 arcsec e_DEdeg Uncertainty on declination (1 sigma)
93-109 F17.10 mJy Ftot Integrated flux density at 54MHz
111-125 E15.7 mJy e_Ftot Uncertainty on flux density at 54MHz
(1 sigma)
127-140 F14.7 mJy/beam Fpeak Peak brightness at 54MHz
142-154 F13.10 mJy/beam e_Fpeak Uncertainty on peak brightness at 54MHz
(1 sigma)
156-166 F11.7 arcsec Maj Major axis
168-179 F12.9 arcsec e_Maj Uncertainty on major axis (1 sigma)
181-191 F11.8 arcsec Min Minor axis
193-207 E15.7 arcsec e_Min Uncertainty on minor axis (1 sigma)
209-221 F13.9 deg PA Position angle
223-235 F13.9 deg E_PA Uncertainty on position angle (1 sigma)
237-247 F11.7 arcsec DCMaj Deconvolved Major axis
249-260 F12.9 arcsec e_DCMaj Uncertainty on deconvolved major axis
(1 sigma)
262-273 F12.9 arcsec DCMin Deconvolved Minor axis
275-289 E15.7 arcsec e_DCMin Uncertainty on deconvolved minor axis
(1 sigma)
291-303 F13.9 deg DCPA Deconvolved position angle
305-317 F13.9 deg e_DCPA Uncertainty on deconvolved position angle
(1 sigma)
319-329 F11.8 mJy/beam Islrms Local rms noise at the source location
331 A1 --- SCode [CMS] Source code (G2)
333-339 A7 --- Mosaic Mosaic identifier (G3)
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Global notes:
Note (G1): The full source name including prefix is 'LoL1JHHMMSS.s+DDMMSS.s',
with HHMMSS.s+DDMMSS.s the centroid coordinates in sexagesimal format.
Note (G2): The source structure code defines the multiplicity of the source
structure in terms of Gaussian components as follows:
S = refers to an isolated single-Gaussian source
C = refers to a single-Gaussian source partly overlapping with other sources
M = is a source fit with multiple Gaussians
Note (G3): The parent mosaic image in which the source detection was
characterised.
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Acknowledgements:
Francesco de Gasperin, fdg(at)ira.inaf.it
(End) Patricia Vannier [CDS] 06-Feb-2023