The FIRST Catalogs: Version History

Current Catalog: 2008 July 16

This catalog from the 1993 through 2004 observations contains 816,331 sources from the north and south Galactic caps. It covers a total of 9055 square degrees of sky (8444 square degrees in the north and 611 square degrees in the south.)

The catalog format differs from the previous version. The contents of the sidelobe flag column has changed to a sidelobe probability estimate, and columns have been added with information on optical and infrared counterparts from the SDSS, GSC2, and 2MASS catalogs.

2003 April 11

This catalog from the 1993 through 2002 observations contains 811,117 sources from the north and south Galactic caps. It covers a total of 9033 square degrees of sky (8422 square degrees in the north and 611 square degrees in the south.)

The catalog format is the same as the previous version.

2001 October 15

This catalog from the 1993 through 2001 observations contains 771,076 sources from the north and south Galactic caps. It covers a total of 8565 square degrees of sky (7954 square degrees in the north and 611 square degrees in the south.)

For this version of the catalog, most of the maps constructed from the previous round of observations (in 1999) were remade to correct a small error in the annual aberration correction (due to a Y2K error in the observation date string.) This led to numerous small changes in the positions and flux densities for sources in the area covered by the 1999 observations. The differences are generally much smaller than the uncertainties: the mean position shift is 0.032 arcsec and the mean flux change is 0.015 mJy, though in rare cases they can be larger.

The catalog format is the same as the previous version.

2000 July 5

This catalog from the 1993 through 2000 observations contains 722,354 sources from the north and south Galactic caps. It covers a total of 7988 square degrees of sky (7377 square degrees in the north and 611 square degrees in the south.)

The catalog format is the same as the previous version.

1999 July 21

This catalog from the 1993 through 1998 observations contains 549,707 sources from the north and south Galactic caps. It covers a total of 6060 square degrees of sky (5450 square degrees in the north and 610 square degrees in the south.)

The catalog format is the same as the previous version. Note that the northern and southern catalogs are now combined into one file.

1998 February 4

This pair of catalogs from the 1993 through 1997 observations contains 382,892 sources from the north Galactic cap and 54,537 sources from the south Galactic cap. In the north it covers about 4150 square degrees of sky, including most of the area 7^h20^m < RA(2000) < 17^h20^m, 22.2° < Dec < 57.6°. In the south it covers about 610 square degrees of sky, including two narrow strips in the area 21^h20^m < RA(2000) < 3^h20^m, -11.5° < Dec < 1.6°.

The catalog format is the same as the previous version.

1997 April 24

This pair of catalogs from the 1993 through 1996 observations contains 236,177 sources from the north Galactic cap and 31,870 sources from the south Galactic cap. In the north it covers about 2575 square degrees of sky, including most of the area 7^h20^m < RA(2000) < 17^h20^m, 22.2° < Dec < 42.5°. In the south it covers about 350 square degrees of sky, including most of the area 21^h20^m < RA(2000) < 3^h20^m, -2.5° < Dec < 1.6°.

This is the first catalog of the southern survey region. It has a different format than previous versions, with additional columns giving the fitted major axis, minor axis, and position angle (before deconvolution). The old format was judged too difficult to use with the elliptical point-spread function of the southern images. The new format also gives the major and minor axes to higher precision than before.

1997 February 27

This catalog contains 236,040 sources from the 1993 through 1996 observations. It covers about 2575 square degrees of sky, including most of the area 7^h20^m < RA(2000) < 17^h20^m, 22.2° < Dec < 42.5°. The format of this catalog is identical to that used for the previous version.

In addition to having 1.7 times as many sources as the previous catalog, both from adding new survey area and from filling in holes in the coverage, this catalog has these changes and improvements:

• The images used for the catalog have had a small emprical rotation and scale change applied, which can shift sources near the grid image corners by up to 0.2 arcsec. Also, higher-order interpolation has been used in summing the overlapping grid images. The result is that the catalog sources have peak flux densities that are systematically slightly higher (by about 0.7%) and sizes that are slightly smaller (typically by 0.15 arcsec in the deconvolved major axis for nearly unresolved sources.) All the data taken to date were reprocessed using the new imaging pipeline. The new coadded images have `E' as the final character of the field name.

• Source positions are also shifted slightly due to the improved maps. Bright sources shift less than 0.2 arcsec (95% shift less than 0.06 arcsec). Fainter sources can shift more due to the changing effects of noise. For the entire catalog, 95% of the sources detected in the previous catalog have moved less than 0.22 arcsec and 99% less than 0.82 arcsec.

• A small fraction (2.5%) of the sources from the previous catalog have disappeared (or moved by more than the 5.4 arcsec beam size). Almost all of these are near the flux detection threshold and have dropped below the level of detectability. Some are in regions where the maps have been improved through the addition of new data. Some are in complex regions where a different set of overlapping Gaussian components was used to model the radio emission. Many were actually sidelobes and were flagged as such in the previous catalog. Note that these same effects can also cause new sources near the detection thresholds to appear in the catalog.

  If you are doing research on sources that have disappeared in this catalog, check their images using the FIRST Cutout Server to see whether they appear to be real sources or not. We would be interested to hear of cases where real radio sources have been omitted from this catalog; the number of such sources is known to be small, however.

• We corrected a mistake in the assignment of field names to sources, so the field name has changed for many sources. We now choose the coadded field in which the source is farthest from any edge.

1996 May 28

This catalog is identical to the 95Oct16 version except for the position angles of sources with fitted minor axes smaller than the 5.4 arcsec beam (i.e. sources with negative values for the deconvolved minor axis.) Those sources all have zero position angles in the 95Oct16 catalog. The majority of such sources are unresolved so that the position angle is indeterminate. However, a minority have unresolved minor axes and resolved major axes; in those cases, the position angles in the 95Oct16 catalog are incorrect and should not be used.

Since this catalog is essentially identical to the previous version (it has the same number of sources, identical positions, and the same sort order), it should be straightforward to switch ongoing research projects based on the 95Oct16 version to the 96May28 catalog.

1995 October 16

This catalog contains 138,665 sources from the 1993 and 1994 observations. It covers about 1550 square degrees of sky, including most of the area 6^h35^m < RA(2000) < 17^h30^m, 28° < Dec < 42°.

In addition to having 5 times as many sources as the previous catalog, this catalog has these changes and improvements:

• The rms noise level is more accurate in fields with bright sources.
• Sources that are probably sidelobes of bright objects are flagged.
• The CLEAN bias correction has been added to flux densities.
• The interpretation of the major and minor axis sizes has changed for unresolved sources.
• The format has changed slightly.

1995 January 6

The initial FIRST catalog was a preliminary release known to have some shortcomings, including regions of bad data. It covered only about 300 square degrees and included 27,000 sources. All this area is included in subsequent higher-quality catalogs. The current catalog is of sufficiently improved quality that it should be used in place of the 95Jan06 version for new or existing research projects. The FIRST image archive at the Space Telescope Science Institute is now fully up-to-date with the current catalog and the cutout server. Access to the full-sized FIRST images is now quite easy and no longer requires a Hubble archive account. The data can be retrieved either through a search interface or through anonymous ftp.