The VLA Low-Frequency Sky Survey Redux (VLSSr)

VLSS-Redux Postage Stamp Server

The National Radio Astronomy Obseratory (NRAO) and the Naval Research Laboratory (NRL) used the NRAO Very Large Array to survey the sky north of a declination of -30 degrees at a frequency of 74 MHz. This postage stamp server is for images from a re-reduction of the survey data (VLSSr), with maps at a resolution of 75 asec and a limiting peak source brightness of about 450 mJy/beam. Final sky coverage of the catalog and images is complete above -10 degrees declination, and extends down to -30 degrees declination at most RAs. In some areas data is available down to declinations of -36 degrees.

Attribution

If you make use of VLSSr data in your work, please reference: Lane, W. M., Cotton, W. D., Helmboldt , J. and Kassim, N. E. 2012 "VLSS Redux: Software Improvements applied to the Very Large Array Low-frequency Sky Survey", Radio Science v. 47, RS0K04

Redux Overview

The VLSSr represents a major improvement over the original VLSS over most of the sky. By using the VLSS as a sky model we were able to better calibrate the ionosphere and image more data, leaving no "holes" in the primary coverage area and improving image dynamic range in most cases. Improved flagging excision techniques allowed us to keep the shortest baselines, increasing the theoretical largest angular scale in the catalog to 36'. An improved primary beam model was applied to correct substantial radially dependent flux errors present in the VLSS. Smart-windowing techniques applied during the cleaning process reduced the point source clean bias by 50% compared to the VLSS. The measured clean bias of 0.66 times the local rms has been corrected in the VLSSr catalog. The VLSSr data are scaled in flux to the Roger, Costain and Bridle (1973 AJ 78 130) flux scale, using the source models in Scaife and Heald (2012 MNRAS 423 30). The VLSSr maps were multiplied by 1.14 to put them onto this scale. The catalog includes 95,000 sources, of which 5% do not have NVSS counterparts. Entire 17 x 17 deg fields can be obtained here or through a simplified form interface. The entire source catalog as a FITS binary table and software here. (Reminder: shift-click will generally force your browser to save the requested image to a file rather than displaying it in a text window.) A catalog browser is also available. Ionospheric climatology using the VLSSr is described here.

Original VLSS

The original reduction products (VLSS) can be obtained
here. The original survey (VLSS) is documented in: Cohen, A. S., Lane, W. M., Cotton, W. D., Kassim, N. E., Lazio, T. J., Perley, R. A. Condon, J., Erickson, W. C. 2006. "The VLA Low Frequency Sky Survey: Methods and Preliminary Results", 2007, AJ, 134, 1245-1262
For detailed general instructions or information about this survey, see the Help File under "general"; or use the links on the forms for help about each item.

The VLSS survey was carried out by the NRAO and the Naval Research Lab.

Equinox:
Object name [optional]:
Central Right Ascension:
Central declination:
Desired image size (degrees):
See Pixel Spacing for size limit.
Pixel spacing:
Desired pixel size in arcseconds
(Min 0.001; max image size 262144 pixels, e.g. 512 x 512)
Projection:
Desired rotation
(N through E) on the sky in degrees. (Use 0.0 for contour plots)
Image Type:
Don't use "FITS Image" unless you have an external viewer configured to activate for fits files in your browser. Also, for JPEG images, you may need to "reload" the image if you've fetched more than one.

Note: The southern completeness limit is -30 degrees but there is decreasing sky coverage to -36 degrees.

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 100 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.



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?



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Modified on Monday, 03-Jun-2013 16:23:10 EDT
Original by Bill Cotton; markup revisions by Pat Murphy.