Astrophysics Group

Cavendish Laboratory


A UK Mirror for the VLA FIRST Survey

Latest coverage available at this Mirror – February 2009

This site is an initiative by MRAO Cambridge to provide improved access for the UK to the images being produced from the FIRST survey. The FIRST survey is an ongoing project using the VLA at 1.4 GHz to provide Faint Images of the Radio Sky at Twenty centimeters. (For the full range of Web-based facilities and documentation, see the FIRST main site ).

Principal Investigators

Robert H. Becker
Department of Physics, University of California, Davis, CA 95616 and IGPP (full address as for Michael Gregg)
Richard L. White
Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218
David J. Helfand
Department of Astronomy, Columbia University, Box 46, Pupin Hall, 538 West 120th Street, New York, NY 10027
Michael D. Gregg
Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, P.O. Box 808, L-413, Livermore, CA 94551-9900

General Description

The FIRST survey began in spring 1993. It uses the VLA at 1.4 GHz and is slated to cover 10,000 square degrees of the Northern Galactic Cap to a sensitivity of about 1 mJy with angular resolution 5.4 arcsec. The image centres lie on a grid at 3-minute time intervals in RA, and at Dec intervals which vary with Dec but approximate to 30 arcmin.

Current Survey Status

The image archive currently held at this site now covers all regions shown in colour in the two coverage maps below.

FIRST Northern coverage July 2008


FIRST Southern coverage July2008

These maps can be used to get a rough idea of the areas covered, but do not provide sufficient resolution for very detailed use. The simplest way to discover whether an image is available for a particular position is to use our postage-stamp server (see below), which will return a message if the position is not covered.

Accessing the Data

We have installed an experimental postage-stamp server to provide a more friendly interface for navigating around the image set and extracting small regions for viewing or downloading. A CONTOUR plot option has now been added – please read the notes on the form before using it! We are indebted to Bill Cotton of NRAO for providing the GNU software from which this server has been adapted. Note that a small image returned by this server will have different gridding and orientation from an image of corresponding position and size returned by the FIRST CUTOUT server at the main site. (The FIRST CUTOUT SERVER cannot be used with the VDQTZ+GZIP compressed noise-quantised FITS-format image archive which is the version held at this Mirror).

The quantisation of the images in this archive allows for more efficient storage and transmission, but incurs a slight degradation in comparison with the FIRST main site versions.

This site may evolve to provide more of the facilities available at the FIRST main site in due course.

The VLA is an instrument of the (USA) National Radio Astronomy Observatory, (NRAO), which is a facility of the (USA) National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Questions, problems or comments about this page? Please contact:  Sally Hales

February 2009