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GMRTAS150M - Giant Metrewave Radio Telescope All-Sky 150-MHz Radio Source Catalog

HEASARC
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Overview

This table contains results from the first full release of a survey of the 150-MHz 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, the authors' automated data-reduction pipeline efficiently processed more than 2000 hours 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, the authors created good quality images for over 95% of the 5,336 pointings. This data release covers 36,900 deg2 (or 3.6 pi steradians) of the sky between -53 and +90 degrees Declination, which is 90% of the total sky. The majority of pointing images has a noise level below 5 mJy/beam (the median RMS background noise is 3.5 mJy per beam), with an approximate resolution of 25" x 25" (or 25" x 25"/cos(Dec-19o) for pointings south of 19 degrees Declination). The authors have produced a catalog of 0.62 Million radio sources with flux densities ranging from 11.1 mJy to 9.22 kJy that are derived from an initial, high-reliability source extraction at the 7-sigma level. For the bulk of the survey, the measured overall astrometric accuracy is better than 2 arcseconds in Right Ascension and Declination, while the flux density accuracy is estimated at approximately 10%.

Within the scope of the TGSS Alternative Data Release (TGSS ADR) project, the source catalog, as well as 5,336 mosaic images (5 x 5 degree2) and an image cutout service, are made publicly available as a service to the astronomical community. (The TGSS images and cutout server are available through the project website at http://tgssadr.strw.leidenuniv.nl/). In addition to enabling a wide range of different scientific investigations, the authors 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-reionization (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 to replace very poor quality observational data, and an improved flux calibration strategy for less severely affected observational data.


Catalog Bibcode

2017A&A...598A..78I

References

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        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in February 2017 based on CDS Catalog J/A+A/598/A78 file table3.dat.

Parameters

Name
The J2000.0 position-based designation of the object, viz., TGSSADR JHHMMSS.s+DDMMSS, where the prefix (given by the authors) stands for 'TIFR GMRT Sky Survey Alternative Data Release'. These names follow the general style recommendations of the CDS Dictionary of Nomenclature of Celestial Objects, e.g., the positional parts are truncated rather than rounded.

RA
The Right Ascension of the source centroid in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-5 degrees (0.036 arcseconds) in the original table.

RA_Error
The 1-sigma uncertainty in the Right Ascension of the source centroid, in arcseconds. The quoted uncertainties are 1-sigma uncertainties resulting from the fitting process, following Condon (1997, PASP, 109, 166). A systematic contribution of 2 arcseconds was added in quadrature to the uncertainties in RA and Dec (see Sect. 4.4 of the reference paper).

Dec
The Declination of the source centroid in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-5 degrees (0.036 arcseconds) in the original table.

Dec_Error
The 1-sigma uncertainty in the Declination of the source centroid, in arcseconds. The quoted uncertainties are 1-sigma uncertainties resulting from the fitting process, following Condon (1997, PASP, 109, 166). A systematic contribution of 2 arcseconds was added in quadrature to the uncertainties in RA and Dec (see Sect. 4.4 of the reference paper).

LII
The Galactic Longitude of the source.

BII
The Galactic Latitude of the source.

Int_Flux_150_MHz
The total (integrated) flux density of the source at 150 MHz, in mJy. For more details on the derived source properties, the authors refer the reader to their PyBDSM documentation at http://www.astron.nl/citt/pybdsm/.

Int_Flux_150_MHz_Error
The uncertainty in the total (integrated) flux density of the source at 150 MHz, in mJy. A systematic scaling error of 10% was added to the statistical uncertainties in the total flux density and peak flux (see Sect. 4.5 of the reference paper).

Flux_150_MHz
The peak flux density of the source at 150 MHz, in mJy/beam. For more details on the derived source properties, the authors refer the reader to their PyBDSM documentation at http://www.astron.nl/citt/pybdsm/.

Flux_150_MHz_Error
The uncertainty in the peak flux density of the source at 150 MHz, in mJy/beam. A systematic scaling error of 10% was added to the statistical uncertainties in the total flux density and peak flux (see Sect. 4.5 of the reference paper).

Major_Axis
The major axis of the Gaussian fit to the source, in arcseconds.

Major_Axis_Error
The 1-sigma uncertainty in the major axis of the Gaussian fit to the source, in arcseconds.

Minor_Axis
The minor axis of the Gaussian fit to the source, in arcseconds.

Minor_Axis_Error
The 1-sigma uncertainty in the minor axis of the Gaussian fit to the source, in arcseconds.

Position_Angle
The position angle (PA) of the Gaussian fit to the source, in degrees.

Position_Angle_Error
The 1-sigma uncertainty in the position angle (PA) of the Gaussian fit to the source, in degrees. The uncertainty was clipped at =/- 90o, which indicates an undetermined PA, e.g., a circular beam.

RMS_150_MHz
The local rms noise computed in a 40 x 40 pixel square centered on the source, in mJy/beam.

Structure_Code
This parameter contains a code that defines the multiplicity of the source structure in terms of Gaussian components: 'S' refers to an isolated single-Gaussian source, 'C' refers to a single-Gaussian source partly overlapping with other sources, and 'M' is a source fit by multiple Gaussians.

Mosaic_Image
The parent image mosaic is the 5 x 5 deg2 image from which the source entry was 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 at http://tgssadr.strw.leidenuniv.nl/.


Contact Person

Questions regarding the GMRTAS150M database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 10-Feb-2017