The FIRST Catalogs: Version History

Since the FIRST survey is a continuing project, the current FIRST catalog is not a final data product. We will periodically release new versions of the catalogs as our sky coverage increases and when improvements are made in the catalog construction process. We make new catalogs publicly available as soon as we have completed the necessary quality checks.

For new projects the most recent version of the catalog is always preferred. However, to make it easier to carry out research projects using the FIRST catalogs, we maintain an archive of all publicly released versions of the catalog. When there are questions about sources that have changed (or disappeared) in a new catalog, it is always possible to go back to the older version of the catalog for comparison.

Here we briefly summarize the changes in the various catalog releases. Catalogs are identified by the date of their release.


Current Catalog: 2014 March 04

This catalog from the 1993 through 2011 observations contains 946,432 sources from the north and south Galactic caps. It covers a total of 10,575 square degrees of sky (8,444 square degrees in the north and 2,131 square degrees in the south.)

The catalog format is the same as the previous version (13Jun05), including information on the mean and rms epoch of observation for each source. As for the 12Feb16 version, the catalog includes a sidelobe probability estimate, and columns have been added with information on optical and infrared counterparts from the SDSS (DR10) and 2MASS catalogs.

In this version of the catalog, images taken in the the new EVLA configuration have been re-reduced using shallower CLEAN thresholds in order to reduce the "CLEAN bias" in those images. Also, the EVLA images are not co-added with older VLA images to avoid problems resulting from the different frequencies and noise properties of the configurations. That leads to small gaps in the sky coverage at boundaries between the EVLA and VLA regions. As a result, the area covered by this release of the catalog is about 60 square degrees smaller than the previous release of the catalog (13Jun05), and the total number of sources is reduced by nearly 25,000. The previous version of the catalog does have sources in the overlap regions, but their flux densities are considered unreliable due to calibration errors. The flux densities should be more accurate in this catalog, biases are smaller, and the incidence of spurious sources is also reduced.

2013 June 05

This catalog from the 1993 through 2011 observations contains 971,268 sources from the north and south Galactic caps. It covers a total of 10,635 square degrees of sky (8444 square degrees in the north and 2191 square degrees in the south.)

The catalog format differs from the previous version. Information on the mean and rms epoch of observation for each source has been added to the catalog. As for the preceding version (12Feb16), the catalog includes a sidelobe probability estimate, and columns have been added with information on optical and infrared counterparts from the SDSS (DR9) and 2MASS catalogs.

2012 February 16

This catalog from the 1993 through 2011 observations contains 946,464 sources from the north and south Galactic caps. It covers a total of 10,635 square degrees of sky (8444 square degrees in the north and 2191 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 and 2MASS catalogs. There is no GSC2 information in this version.

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 7h20m < RA(2000) < 17h20m, 22.2° < Dec < 57.6°. In the south it covers about 610 square degrees of sky, including two narrow strips in the area 21h20m < RA(2000) < 3h20m, -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 7h20m < RA(2000) < 17h20m, 22.2° < Dec < 42.5°. In the south it covers about 350 square degrees of sky, including most of the area 21h20m < RA(2000) < 3h20m, -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 7h20m < RA(2000) < 17h20m, 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:

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 6h35m < RA(2000) < 17h30m, 28° < Dec < 42°.

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

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.

XXX

Over most of the survey area, the detection limit is 1 mJy. A region along the equatorial strip (RA = 21.3 to 3.3 hrs, Dec = -1 to 1 deg) has a deeper detection threshold because two epochs of observation were combined. The typical detection threshold in this region is 0.75 mJy. There are approximately 4,500 sources below the 1 mJy threshold used for most previous versions of the catalog.

The catalog is on-line and can be searched using the FIRST Search Engine. However, for large-scale investigations it will be necessary to obtain the complete catalog. This document describes the catalog format.

The catalog is sorted by decreasing declination and has the following format:

#                                                                                                               ------SDSS------ -----2MASS----  Epoch     Epoch     Epoch  
#  RA           Dec        P(S)    Fpeak      Fint    RMS     Maj    Min   PA    fMaj   fMin   fPA Field         #  Sep    i  Cl  #  Sep    K   Mean-yr   Mean-MJD   rms-MJD
07 27 34.289 +64 40 59.80 0.197     1.00      1.12   0.139   2.13   1.58   0.2   5.80   5.63   0.2 07300+64243J -1 99.00 99.00 -  1  6.76 14.62 2002.687 2452526.1     0.002
07 38 39.304 +64 40 16.28 0.014     2.39      5.73   0.139   9.31   3.58 136.6  10.76   6.48 136.6 07360+64243J -1 99.00 99.00 -  0 99.00 99.00 2002.687 2452526.1     0.001
07 50 24.019 +64 40 01.21 0.014    22.09     24.00   0.140   1.96   1.13   6.8   5.74   5.52   6.8 07480+64243J -1 99.00 99.00 -  0 99.00 99.00 2002.687 2452526.1     0.002
07 38 45.622 +64 39 50.12 0.014     2.39      4.33   0.140   6.43   3.27  13.5   8.40   6.31  13.5 07360+64243J -1 99.00 99.00 -  0 99.00 99.00 2002.687 2452526.1     0.000
07 39 32.799 +64 39 18.03 0.082     1.41      1.25   0.139   2.63   0.00  37.5   6.01   4.30  37.5 07420+64243J -1 99.00 99.00 -  0 99.00 99.00 2002.687 2452526.1     0.002

The format of this catalog is the same as the previous release (13Jun05) but differs from earlier versions of the catalog. The last 3 columns give information on the epoch of observation for each source and are described below in the observation epoch section. The P(S) column, which indicates the probability that the source is a sidelobe, replaces the previous binary sidelobe flag column. The columns following the field name give information on counterparts to the FIRST source in the SDSS DR10 catalog and the 2MASS catalog. These parameters are described in detail below in the description of the P(S) column and the counterparts columns. Other catalog columns are common with FIRST catalog releases extending back over the past decade.


The catalog history page describes previously released versions of the FIRST catalogs, which are still available for historical purposes. We recommend that the new catalog be used where possible for all projects.