8051 VIII/51 the FIRST Survey, version 1998Feb R L White R H Becker D J Helfand M D Gregg Astrophys. J. 475 479 1998 1997ApJ...475..479W http://sundog.stsci.edu/ : home page of the VLA FIRST Survey http://sundog.stsci.edu/first/catalogs/history.html : Version History http://sundog.stsci.edu/cgi-bin/searchfirst : the FIRST search engine http://third.llnl.gov/cgi-bin/firstcutout : the FIRST Cutout Server. http://www.cv.nrao.edu/first/ : FIRST page at NRAO Radio sources Surveys The FIRST survey to produce Faint Images of the Radio Sky at Twenty centimeters began in 1993. It uses the VLA (Very Large Array, a facility of the National Radio Observatory (NRAO)) at a frequency of 1.4GHz, and it is slated to 10,000 deg^2^ to a sensitivity of about 1mJy with an angular resolution of about 5". The co-added images are available on the Internet (see the FIRST home page at http://sundog.stsci.edu/ for details). The source catalogue is derived from the images. This version of the FIRST Survey is derived from the 1993 through 1997 observations, and contains 382,892 sources for the north Galactic cap, and 54,537 sources for the south Galactic cap. The northern catalog covers about 4150 square degrees of sky, including most of the area: 7h20m < RA(2000) < 17h20m 22.2{deg} < Dec < 57.6{deg} The southern catalog covers about 610 square degrees of sky, including two narrow strips in the area 21h20m < RA(2000) < 3h20m -11.5{deg} < Dec < 1.6{deg}

FIRST FIRST Source designation This column (not part of the original catalog) contains the source name built from the rule registered at IAU ('J' followed by truncated J2000-position) --- RAh Right Ascension J2000 (hours) Position position (J2000) of the source. The accuracy of the position depends on the brightness and size of the source and the noise in the map. Point sources at the detection limit of the catalog have positions accurate to better than 1 arcsec at 90% confidence; 2 mJy point sources in typically noisy regions have positions good to 0.5 arcsec. An empirical expression for the positional accuracy is unc(90% confidence) = Size (1/SNR + 1/20) arcsec where Size is either the major or minor axis fitted FWHM (fMaj or fMin) as given in the catalog and SNR is the peak flux density signal-to-noise ratio: SNR = (Fpeak-0.25) / Rms (The positional uncertainty is of course elliptical for elliptical sources.) The best possible positional uncertainty is limited to about 0.1 arcsec by our ability to fit source positions in maps with 1.8 arcsec pixels and by various random calibration uncertainties. Systematic errors in the positions are smaller than 0.05 arcsec. h RAm Right Ascension J2000 (minutes) min RAs Right Ascension J2000 (seconds) s DE- Declination J2000 (sign) --- DEd Declination J2000 (degrees) deg DEm Declination J2000 (minutes) arcmin DEs Declination J2000 (seconds) arcsec Wflag Warning flag `W' is a warning flag indicating that the source may be a sidelobe of a nearby bright source. In the northern catalog, 14,039 sources (3.7%) are flagged as possible sidelobes; in the southern catalog, 1,943 sources (3.6%) are flagged as possible sidelobes. The flagging algorithm is an artificial intelligence approach based on oblique decision trees. Our analysis indicates that <10% of the objects flagged as sidelobes are real sources and that considerably less than 1% of the unflagged sources in the catalog are sidelobes. Complete details of the sidelobe identification procedure are included in our catalog paper. NOTE: The sidelobe flagging in the southern catalog may not be as reliable as in the north because the sidelobe characteristics change with the zenith angle of the observation. We are working on improvements to the sidelobe-flagging, but for now it is important to be cautious in studies of individual southern sources. We recommend checking the images using the FIRST Cutout Server if there is any doubt about the reality of particular sources (in either the north or the south.) This is easily done when using the FIRST Search Engine to search the catalog, since each source selected in the search has a link to the Cutout Server. --- Fpeak Peak flux density at 1.4GHz Fpeak and Fint are the peak and integrated flux densities measured in mJy. They are derived by fitting an elliptical Gaussian model to the source. To correct for the ``CLEAN bias'' effect, 0.25 mJy has been added to the peak flux density and the integrated flux density has been multiplied by (1+0.25/Fpeak) (see our Astrophysical Journal paper and our catalog paper for more details.) The uncertainty in Fpeak is given by the rms noise at the source position, while the uncertainty in Fint can be considerably greater depending on the source size and morphology. For bright sources the accuracies of Fpeak and Fint are limited to about 5% by systematic effects. Note that for sources that are not well-described by an elliptical Gaussian model, Fint is not an accurate measure of the integrated flux density. mJy Fint Integrated flux density at 1.4GHz mJy Rms Local noise estimate Rms is a local noise estimate at the source position measured in mJy. Rms is computed by combining the measured noise from all grid pointing images contributing to this coadded map position. Note that the significance of detection for a source is (Fpeak-0.25)/Rms, not Fpeak/Rms, because of the CLEAN bias correction to the peak flux density. The catalog includes only sources brighter than 5 Rms. FITS images giving the rms noise as a function of position on the sky are available for the northern and the southern areas. These images give the rms in mJy/beam tabulated on a ~3 arcmin grid in RA and Declination. If there is no source in the catalog at a given position, the source peak flux density (before CLEAN bias correction) is less than 5 times the coverage map rms value at that position. mJy MajAxis Major axis (FWHM) MajAxis, MinAxis, and PA give the major and minor axes (FWHM in arcsec) and position angle (degrees east of north) derived from the elliptical Gaussian model for the source. MajAxis and MinAxis have been deconvolved to remove blurring by the elliptical Gaussian point-spread function. (The fitted parameters before deconvolution are given in the fMaj, fMin, and fPA columns.) In the north the beam is circular 5.4 arcsec FWHM; in the south it is elliptical, 6.4x5.4 arcsec FWHM, with the major axis running north-south. Noise can cause the fitted values of the major and minor axes (before deconvolution) to be smaller than the beam. The corresponding deconvolved size is given as zero in those cases. The uncertainties in the deconvolved sizes depend on both the brightness and the sizes. Objects at the catalog flux density limit have uncertainties of about 2 arcsec in their sizes (so faint objects with Maj < 2 arcsec are consistent with point sources.) An simple empirical estimate of the uncertainty is Sigma(Size) = 10 arcsec (1/SNR + 1/75) where SNR is the signal-to-noise ratio defined above. arcsec MinAxis Minor axis (FWHM) arcsec PA Position angle deg fMaj Fitted MajAxis before deconvolution fMaj, fMin, and fPA give the major and minor axes (FWHM in arcsec) and position angle (degrees east of north) derived from the elliptical Gaussian model for the source. These are the fitted sizes measured directly from the image; the elliptical point-spread function has not been deconvolved. arcsec fMin Fitted MinAxis before deconvolution arcsec fPA Fitted PA before deconvolution deg Field Name of the coadded image containing the source The Field Name is the name of the coadded image containing the source. Note that the field name encodes the position of the field center: field hhmmm+ddmmm is centered at RA=hh mm.m, Dec=+dd mm.m. The images are available from several archives and through the FIRST Cutout Server. All field names in the current catalog end with E or F, indicating that they were constructed using the imaging pipeline that applies a small rotation and scale correction. See the catalog history page for more information. The F fields are new in this catalog, while sources extracted from the E fields are identical to those in the previous version of the catalog. Some E fields from the last catalog have been replaced by new F fields because there were additional grid images available for the coadding. --- Richard L. White STScI 1998Feb04 UNKNOWN UNKNOWN The files (originally catalog_north_98feb04.bin and catalog_south_98feb04.bin) were copied from http://sundog.stsci.edu/first/catalogs/readme.html The preceding version (1997 April 24) was numbered <VIII/48> in CDS Archives. See http://sundog.stsci.edu/first/catalogs/history.html for the complete version history. VIII_51.xml