Images from the FIRST Survey

The final images from FIRST, produced by coadding the twelve (or sometimes more) single-field pointings adjacent to each pointing center, have 1.8" pixels, a typical rms of 0.15 mJy, and a resolution of 5". At the 1 mJy source detection threshold, there are ~90 sources per square degree, ~35% of which have resolved structure on scales from 2-30".

Note that the images are fairly large, typically 1150x1550 pixels = 7.1 Mbytes to cover a 34.5 arcmin x 46.5 arcmin = 0.45 square degree area of the sky. A 10 pixel strip at the top of each image contains a copyright notice.

The most convenient access to the FIRST images is through the FIRST Cutout Server, which allows an image section to be extracted from the coadded image database at a user-specified position. The cutout server is also linked to the FIRST Search Engine, so that the catalog can be searched for sources of interest and then images can be obtained for those objects. All images taken through 2011 are available through the cutout server.

The full images are also available. The coadded images from the 1993 through 2011 observations are archived in the Multimission Archive at Space Telescope (MAST) at the Space Telescope Science Institute. Access to the images is simple through the search interface; the images are also available via anonymous ftp at

A subset of the images can also be obtained via ftp from the National Radio Astronomy Observatory. Since NRAO's image collection is incomplete we recommend that the STScI archive be used instead. One difference between the archives is that the NRAO versions of the images have been quantized to make them more compressible using gzip. They are consequently faster to transfer over the network, but they are slightly degraded compared with the images available from STScI and the FIRST Cutout Server.