J/A+A/598/A78 The GMRT 150MHz all-sky radio survey (Intema+, 2017)
The GMRT 150 MHz all-sky radio survey. First alternative data release TGSS ADR1.
Intema H.T., Jagannathan P., Mooley K., Frail D.A.
<Astron. Astrophys. 598, A78 (2017)>
=2017A&A...598A..78I 2017A&A...598A..78I (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio continuum
Keywords: surveys - catalogs - radio continuum: general -
techniques: image processing
Abstract:
We present the first full release of a survey of the 150MHz radio
sky, observed with the Giant Metrewave Radio Telescope (GMRT) between
April 2010 and March 2012 as part of the TIFR GMRT Sky Survey (TGSS)
project. Aimed at producing a reliable compact source survey, our
automated data reduction pipeline efficiently processed more than
2000h of observations with minimal human interaction. Through
application of innovative techniques such as image-based flagging,
direction-dependent calibration of ionospheric phase errors,
correcting for systematic offsets in antenna pointing, and improving
the primary beam model, we created good quality images for over 95
percent of the 5336 pointings. Our data release covers 36900deg2 (or
3.6πsteradians) of the sky between -53° and +90°
declination (Dec), which is 90 percent of the total sky. The majority
of pointing images have a noise level below 5mJy/beam with an
approximate resolution of 25"x25" (or 25"x25"/cos(Dec-19°) for
pointings south of 19° declination). We have produced a catalog of
0.62 Million radio sources derived from an initial, high reliability
source extraction at the seven sigma level. For the bulk of the
survey, the measured overall astrometric accuracy is better than two
arcseconds in right ascension and declination, while the flux density
accuracy is estimated at approximately ten percent. Within the scope
of the TGSS alternative data release (TGSS ADR) project, the source
catalog, as well as 5336 mosaic images (5°x5°) and an image
cutout service, are made publicly available at the CDS as a service to
the astronomical community. Next to enabling a wide range of different
scientific investigations, we anticipate that these survey products
will provide a solid reference for various new low-frequency radio
aperture array telescopes (LOFAR, LWA, MWA, SKA-low), and can play an
important role in characterizing the epoch-of-reionisation (EoR)
foreground. The TGSS ADR project aims at continuously improving the
quality of the survey data products. Near-future improvements include
replacement of bright source snapshot images with archival targeted
observations, using new observations to fill the holes in sky coverage
and replace very poor quality observational data, and an improved flux
calibration strategy for less severely affected observational data.
Description:
We provide the first full public release of the 150 MHz continuum
survey (TGSS) from the Giant Metrewave Radio Telescope. The resulting
images cover the full sky north of DEC -53 degrees (or 36,900 square
degrees) with a median RMS background noise of 3.5mJy per beam and a
typical resolution of 25". Our final radio source catalog contains
0.62 million sources with flux densities ranging from 11.1mJy to
9.22kJy.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 149 623604 Full source catalog of TGSS ADR1 150 MHz sources
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- TGSSADR Name without prefix (JHHMMSS.S+DDMMSS) (1)
19- 27 F9.5 deg RAdeg Centroid right ascension (J2000)
30- 33 F4.1 arcsec e_RAdeg Uncertainty on right ascension (1 sigma)
36- 44 F9.5 deg DEdeg Centroid declination (J2000)
47- 50 F4.1 arcsec e_DEdeg Uncertainty on declination (1 sigma)
53- 61 F9.1 mJy Stotal Total (integrated) flux density at 150MHz
64- 71 F8.1 mJy e_Stotal Uncertainty on Stotal (1 sigma)
74- 82 F9.1 mJy/beam Speak Peak flux at 150MHz
85- 92 F8.1 mJy/beam e_Speak Uncertainty on Speak (1 sigma)
95- 99 F5.1 arcsec Maj Gaussian fit major axis
102-105 F4.1 arcsec e_Maj Uncertainty on Maj (1 sigma)
108-112 F5.1 arcsec Min Gaussian fit minor axis
115-118 F4.1 arcsec e_Min Uncertainty on Min (1 sigma)
121-125 F5.1 deg PA [] Gaussian fit position angle (2)
128-131 F4.1 deg e_PA Uncertainty on PA (1 sigma)
133-138 F6.1 mJy/beam Noise Local image background RMS noise
141 A1 --- Code [SCM] Source structure code (S/C/M) (3)
144-149 A6 --- Mosaic Name of parent mosaic image (4)
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Note (1): The full source name including prefix is 'TGSSADR JHHMMSS.S+DDMMSS',
with HHMMSS.S+DDMMSS the centroid coordinates in sexagesimal format
following the IAU truncation standard.
Note (2): The PA uncertainty is clipped at 90 degrees, which indicates an
undetermined PA (e.g. a circular beam).
Note (3): 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 (4): The parent image mosaic is the 5x5 deg2 image from which the source
entry is extracted. Mosaic names are formatted as 'RxxDyy', with xx being a
zero-padded RA index running from 01 to 72, and yy a zero-padded DEC index
running from 00 to 85. A list of mosaic names and their center coordinates is
provided through the TGSS ADR project website:
http://tgssadr.strw.leidenuniv.nl
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Acknowledgements:
Huib Intema, intema(at)strw.leidenuniv.nl
(End) Huib Intema [Leiden Obs./NRAO], Patricia Vannier [CDS] 05-Dec-2016