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NVSS Image ftp service (5 August 1998)

NVSS Image ftp service

The form on this Web page allows specifying a celestial position for which the full 4x4 degree NVSS FITS image is desired. This avoids having to determine which file is desired. Various options for accessing the image are available.

The NRAO/VLA Sky Survey (NVSS) is a radio survey using the NRAO Very Large Array telescope and covers the sky north of a declination of -40 degrees at a frequency of 1.4 GHz, a resolution of 45" and a limiting peak source brightness of about 2.5 mJy/beam. Linear polarization (Q, U) as well as total intensity (I) measurments are made. The survey is substantially complete - just a very few of the images contain small, isolated holes which may be filled in by reobservation in spring 1999.

Other services of the NVSS survey include:

For detailed general instructions click here or for more about a form entry click on its label.

Equinox: B1950 J2000 Polarization: Stokes I IQU

Central Right Ascension: hh mm ss.ss

Central declination: (+/-)dd mm ss

Type: link to file gzipped FITS image gzipped FITS file

Don't use "FITS image" unless you have an external FITS viewer that can display gzip compressed FITS images. Note: direct FITS image are gzip compressed; use "html" and ask for the uncompressed file if you system does not support gzip compression. However, uncompressed file are 2 to 12 Mbyte in size and take a long time to transfer; the compressed files are generally a factor of 7 smaller.

Click to request the image,

Note: these images will have a relatively high dynamic range which will cause them to appear as white dots on a black background unless the viewer used has suitable control over brightness, contrast and the range of values to be displayed. The "noise" level in these images is about 0.5 mJy/beam.

The FITSview family of FITS image viewers is available for a variety of computer systems. For a short discussion of installing external viewers for FITS files click here.

In publications using NVSS results please reference Condon, et al. 1998, AJ, 115, 1693; a preprint of this paper which describes the design and techniques of the NVSS is available here. The NVSS survey is substantially complete, missing only small, isolated holes. For the very latest information and detailed descriptions of the NVSS survey see its main site home page.

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.

Other Sources of FITS Images from Sky Surveys

The (USA) National Radio Astronomy Observatory (NRAO) is operated by Associated Universities, Inc. and is a Facility of the (USA) National Science Foundation.

Comments? Questions? Problems?
bcotton@nrao.edu

Any problems with the UK server?

segh@mrao.cam.ac.uk