Getting Started

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 quite 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 images are now accessible via anonymous ftp. The data are organized by RA in subdirectories with format HHMMM. Users may either download the data through the browser or:

ftp archive.stsci.edu (logon as anonymous) cd /pub/vla_first/data/
dir (to list the directories)
binary
get/mget filenames

User may search for the coadded image with the MAST search interface. The data may be downloaded by clicking on the Data ID.

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.

Users should read the description of the VLA FIRST project.

The images can also be obtained via ftp from the National Radio Astronomy Observatory. Note 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.

Information on this page taken from VLA-FIRST web site.