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NVSS - NRAO VLA Sky Survey Catalog

HEASARC
Archive

Overview

This table contains the National Radio Astronomy Observatory (NRAO) Very Large Array (VLA) Sky Survey, the so-called NVSS Catalog. The NVSS Catalog covers the sky north of the J2000.0 Declination of -40 degrees (82% of the celestial sphere) at 1.4 GHz. The principal data products of the NVSS were (1) a set of 2326 4 degree by 4 degree continuum "cubes" with three planes containing Stokes I, Q, and U images, plus (2) a catalog of almost 2 million discrete sources stronger than a flux density S of about 2.5 mJy. The images all have 45 arcsecond FWHM angular resolution and nearly uniform sensitivity. Their rms brightness fluctuations are approximately 0.45 mJy/beam = 0.14 K (Stokes I) and approximately 0.29 mJy/beam = 0.09 K (Stokes Q and U). The rms uncertainties in right ascension and declination vary from <= ~1 arcsecond for the 400,000 sources stronger than 15 mJy to 7 arcseconds at the survey limit. The NVSS was made as a service to the astronomical community. All data products, user software, and updates were released via the World-Wide Web as soon as they were produced and verified. For more complete information on the NVSS, please refer to the NVSS website at http://www.cv.nrao.edu/nvss/

Catalog Bibcode

1998AJ....115.1693C

References

1.4GHz NRAO VLA Sky Survey (NVSS)
   Condon J.J., Cotton W.D., Greisen E.W., Yin Q.F., Perley R.A., Taylor G.B.
   and Broderick J.J.
   <Astron. J. 115, 1693 (1998)>

The NRAO VLA Sky Survey (NVSS)
   http://www.cv.nrao.edu/nvss/

Provenance

This table was created by the HEASARC in October 2002 based on the file ftp://ftp.cv.nrao.edu/nvss/CATALOG/NVSSCatalog.text.gz provided by the NVSS Catalog's authors. It was updated by the HEASARC in June 2009 to fix a problem with the original ingest in which the leading digit of some flux fields was lost.

Data Products

The NVSS project at NRAO maintains an FTP archive of the (u,v) data and images from which the source catalog was constructed. These files are available as remote data products linked to the entries in the HEASARC implementation of the NVSS source catalog. Clicking on a data product link for a given source will fetch the (u,v) and/or image data for the field in which the selected source was found. The large (4 degree X 4 degree) maps and their associated multisource (u,v) data sets are stored by NRAO as binary files in FITS format. The naming conventions of these files are as follows. Each map is named after the J2000 right ascension and declination of its center, and the first letter specifies the polarization plane(s). For example, C2230P84.gz is the map cube with Stokes I, Q, and U planes centered on right ascension = 22h 30m, declination = +84 deg. I0224M32.gz contains only the total-intensity plane centered on right ascension 02h 24m, declination -32 deg. The corresponding total intensity map file is I2230P84.gz, and the corresponding multisource (u,v) data file is called J0224-32.MS. The compressed map cubes are about 1.7 megabytes in size, and the total-intensity maps are smaller (about 0.7 megabytes) for faster access by users not interested in linear polarization. Please note that not every NVSS survey field will have a corresponding multisource (u,v) data file.

Parameters

Name
The NVSS Catalog designation of the form NVSS JHHMMSS+DDMMSS, using the standard IAU nomenclature prescription, where NVSS is the catalog acronym, J specifies the coordinate equinox (either "J" for J2000.0 or "B" for B1950.0), HHMMSS are the hours, minutes, and truncated (not rounded) seconds of right ascension, + or - is the sign of the declination, and DDMMSS are the degrees, arcminutes, and truncated (not rounded) arcseconds of declination. Thus, the NVSS source at equinox J2000.0 coordinates of 00h 00m 00.24s, = -20d 04' 49.1" is called NVSS J000000-200449. There are four cases where there are pairs of sources which are so close together that their names would be identical according to this schema (see below), and the HEASARC has added suffixes of 'a' (for the source with the smaller RA) and 'b' (for the source with the larger RA) in such cases in order to differentate them.

  |Name                |RA (J2000)|Dec (J2000)
  |                    | degrees  |  degrees
  |NVSS J093731-102001a|144.381833|-10.333833
  |NVSS J093731-102001b|144.383000|-10.333750
  |NVSS J133156-121336a|202.986708|-12.226750
  |NVSS J133156-121336b|202.987167|-12.226667
  |NVSS J160612+000027a|241.552917|  0.007611
  |NVSS J160612+000027b|241.553625|  0.007639
  |NVSS J215552+380029a|328.967375| 38.008111
  |NVSS J215552+380029b|328.968792| 38.008139
  

RA
The Right Ascension of the centroid of the fitted radio source in the selected equinox and for the epoch of observation 1995 +/- 2. This was given in equinox J2000 and with a precision of 0.01 seconds of time in the original table.

Dec
The Declination of the centroid of the fitted radio source in the selected equinox and for the epoch of observation 1995 +/- 2. This was given in equinox J2000 and with a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the centroid of the fitted radio source.

BII
The Galactic Latitude of the centroid of the fitted radio source.

RA_Error
The rms uncertainty in the Right Ascension, in seconds of time.

Dec_Error
The rms uncertainty in the Declination, in arcseconds.

Flux_20_cm
The integrated 1.4-GHz flux density of the radio source, in milliJanskies (mJy).

Flux_20_cm_Error
The rms uncertainty in the 1.4-GHz flux density of the radio source, in milliJanskies (mJy).

Limit_Major_Axis
A limit flag parameter for the fitted major axis of the radio source which is set to '<' if it is not significantly resolved.

Major_Axis
The fitted (deconvolved) major axis of the radio source, in arcseconds.

Major_Axis_Error
The rms uncertainty in the fitted major axis of the radio source, in arcseconds.

Limit_Minor_Axis
A limit flag parameter for the fitted minor axis of the radio source which is set to '<' if it is not significantly resolved.

Minor_Axis
The fitted (deconvolved) minor axis of the radio source, in arcseconds.

Minor_Axis_Error
The rms uncertainty in the fitted minor axis of the radio source, in arcseconds.

Position_Angle
The position angle of the fitted major axis of the radio source, in degrees.

Position_Angle_Error
The rms uncertainty in the position angle of the fitted major axis of the radio source, in degrees.

Residual_Code
A code flag parameter for the residuals to the fit to the radio source which is set to 'P' if the peak flux density residual was high, or 'S' if the integrated flux density of the residual was high, and is otherwise left blank. Non-blank values of this parameter are typically indicative of complex source structure.

Residual_Flux
In cases where the value of the residual_code parameter is non-blank, this parameter gives the peak residual, in units of mJy/beam.

Pol_Flux
The integrated linearly polarized flux density (sqrt{Q2 + U2}) of the radio source, in milliJanskies (mJy). A bias correction has been subtracted from the measured value which can sometimes cause (unphysical) negative values. A complete discussion of this issue is given in Section 5.2.6 of the NVSS paper by Condon et al. (1998, AJ, 115, 1693).

Pol_Flux_Error
The rms uncertainty in the integrated linearly polarized flux density, in milliJanskies (mJy).

Pol_Angle
The position angle of the "E" vector of the linear polarization on the sky, if the source was detected (1 sigma) in linear polarization, in degrees.

Pol_Angle_Error
The rms uncertainty in the linear polarization angle, in degrees.

Field_Name
The name of the original survey image field from which the component was derived.

X_Pixel
The X position (in the RA direction) of the pixel where the radio source was located in the original survey image field.

Y_Pixel
The Y position (in the Declination direction) of the pixel where the radio source was located in the original survey image field.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 22-Jun-2012