Help for FIRST Cutout Extractions

The FIRST cutout page allows you to extract a section of an image from the FIRST 1400 MHz sky survey. The images have 1.8 arcsec pixels with a FWHM resolution of 5.4 arcsec.

Why might you want to obtain FIRST images rather than rely on the FIRST catalog for source information? The catalog is only complete to 5 times the map rms noise level (typically 0.75 mJy), so even in cataloged parts of the sky, faint uncataloged sources may be found. Also, while the elliptical Gaussian source models used in the catalog do a reasonably good job of capturing the structure of extended sources, complex sources have structure than can only be fully appreciated by examining the original image data. Finally, faint cataloged sources are sometimes sidelobes from nearby bright sources. While we attempt to flag such sources in the catalog, the human eye is still better at recognizing spurious sources.

The FIRST survey covers two regions:

The edges of the covered areas are a little ragged, but the coverage is now continuous with no significant embedded holes. For more details of the sky coverage, see the FIRST coverage maps. There are 34000 images comprising about 250 Gbytes of data. All of these images are available on our image server.

Cutout Extraction Form Parameters

The form allows you to specify the position and size of the extracted image, the type of the returned image (FITS or GIF), and, for GIF images, the intensity scaling used to display the image.