The NRAO VLA Sky Survey (GMRT MIRROR site)

J. J. Condon, W. D. Cotton, E. W. Greisen, and Q. F. Yin

National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903

R. A. Perley and G. B. Taylor

National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801

J. J. Broderick

Physics Department, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

• A set of 2326 continuum image ``cubes,'' each covering 4 deg X 4 deg with three planes containing the Stokes I, Q, and U images. These images were made with a relatively large restoring beam (45 arcsec FWHM) to yield the high surface-brightness sensitivity needed for completeness and photometric accuracy. Their rms brightness fluctuations are about 0.45 mJy/beam = 0.14 K (Stokes I) and 0.29 mJy/beam = 0.09 K (Stokes Q and U). The rms uncertainties in right ascension and declination vary from < 1 arcsec for relatively strong (S > 15 mJy) point sources to 7 arcsec for the faintest (S = 2.3 mJy) detectable sources. The completeness limit is about 2.5 mJy.
• A catalog of discrete sources on these images (over 1.8 million sources in the entire survey).
• Processed (u,v) data sets. Every large image was constructed from more than 100 smaller "snapshot" images. All of the edited and calibrated single-source (u,v) data sets used to make the snapshot images contributing to each large image have been combined into a single multisource (u,v) file for users who want to investigate the data underlying the images.

The NVSS has been made as a service to the astronomical community. Users should read the postscript paper (about 4.7 megabytes) for an overview of the NVSS. If you use the NVSS, please reference it as: Condon, J. J., Cotton, W. D., Greisen, E. W., Yin, Q. F., Perley, R. A., Taylor, G. B., & Broderick, J. J. 1998, AJ, 115, 1693.

The sky positions of the large NVSS images are shown in the image grid plot. These images are in FITS format. The full 4 deg X 4 deg FITS image cubes are available via image cubes. You may also view (as either gray-scale images or contour plots) and/or copy selected subimages using our postage stamp server.

We extracted a source catalog from each image by fitting elliptical Gaussians to all significant peaks. The individual catalogs have been merged into the master catalog of sources from all images. See the catalog description for details about the cataloged source parameters. An NVSS catalog browser is available, but please exercise caution (don't ask for a catalog of the whole sky!). The user program NVSSlist can display selected portions of the catalog. Both the catalog browser and NVSSlist correct the raw catalog for known biases and computes errors associated with the source model parameters (position, flux density, etc.) using equations derived in Condon, J. J. 1997, PASP, 109, 166. To interpret the catalog results in complex or crowded fields, users should look at contour plots (available on the postage stamp server) showing the actual brightness distributions from which sources were extracted.

Users of the AIPS task IMAGR often need to image extra fields covering nearby confusing sources. A RUN file generator produces the required list of field offsets for NVSS sources whose flux densities, attenuated by the primary beam, exceed a chosen cutoff.

To avoid ambiguity, please refer to NVSS sources using the standard IAU format NVSS EHHMMSS+DDMMSS, with E = J for equinox J2000 or E = B for equinox B1950 coordinates, HHMMSS the hours, minutes, and truncated (not rounded) seconds of right ascension, the declination sign (+ or -), and DDMMSS the degrees, minutes, and seconds (truncated, not rounded) of declination. Thus the NVSS source at J2000 RA = 00 00 00.24, DEC = -20 04 49.2 (= B1950 RA = 23 57 26.34, DEC = -20 21 31.5) should be called NVSS J000000-200449 or NVSS B235726-202131.

• This page has been modularised to help locate the topic you require.

• The ongoing VLA Low-frequency Sky Survey ( VLSS) will also be mirror'ed soon.

For more information about the NVSS, contact jcondon@nrao.edu