VIII/90 The FIRST Survey Catalog, Version 12Feb16 (Becker+ 2012)
The FIRST Survey Catalog, Version 2012 Feb Becker R.H., Helfand D.J., White R.L., Gregg M.D., Laurent-Muehleisen S.A. <Astrophys. J. 475, 479 (1997)> =1997ApJ...475..479W =2012yCat.8090....0B
ADC_Keywords: Radio sources ; Surveys Description: The Faint Images of the Radio Sky at Twenty centimeters (FIRST) 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 deg2 of the North and South Galactic Caps, to a sensitivity of about 1mJy with an angular resolution of about 5''. The images produced by an automated mapping pipeline have pixels of 1.8'', a typical rms of 0.15mJy, and a resolution of 5''; the 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 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 the 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. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file first12.dat 160 946464 The FIRST survey catalog, 12Feb16 Version
See also: 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.ucllnl.org/cgi-bin/firstcutout : the FIRST Cutout Server. Byte-by-byte Description of file: *.dat
Bytes Format Units Label Explanations
1- 16 A16 --- FIRST FIRST Source designation (1) 18- 19 I2 h RAh Right Ascension J2000 (hours) (2) 21- 22 I2 min RAm Right Ascension J2000 (minutes) (2) 24- 29 F6.3 s RAs Right Ascension J2000 (seconds) (2) 31 A1 --- DE- Declination J2000 (sign) (2) 32- 33 I2 deg DEd Declination J2000 (degrees) (2) 35- 36 I2 arcmin DEm Declination J2000 (minutes) (2) 38- 42 F5.2 arcsec DEs Declination J2000 (seconds) (2) 44- 48 F5.3 --- p(S) [0,1] Probability of being a side lobe (3) 50- 57 F8.2 mJy Fpeak Peak flux density at 1.4GHz (4) 59- 67 F9.2 mJy Fint Integrated flux density at 1.4GHz (4) 70- 75 F6.3 mJy Rms Local noise estimate (5) 77- 82 F6.2 arcsec MajAxis Major axis (FWHM) (6) 84- 89 F6.2 arcsec MinAxis Minor axis (FWHM) (6) 91- 95 F5.1 deg PA [0/180] Position angle (6) 97-102 F6.2 arcsec fMaj Fitted MajAxis before deconvolution (7) 104-109 F6.2 arcsec fMin Fitted MinAxis before deconvolution (7) 111-115 F5.1 deg fPA [0/180] Fitted PA before deconvolution (7) 117-128 A12 --- Field Name of the coadded image containing the source (8) 130-131 I2 --- N1 [0/10]?=-1 Number of SDSS-DR8 counterparts (9) 133-137 F5.2 arcsec r1 [0/8]?=99 Closest SDSS match (9) 139-143 F5.2 mag m1 ?=99 SDSS i magnitude of closest SDSS match (9) 145 A1 --- c1 [sg-] SDSS class: s=star, g=galaxy 147-148 I2 --- N2 Number of 2MASS counterparts (10) 150-154 F5.2 arcsec r2 [0/8]?=99 Closest 2MASS match (10) 156-160 F5.2 mag m2 ?=99 2MASS Ks mag. of closest 2MASS match (10)
Note (1): 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) Note (2): 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. Note (3): p(S) indicates the probability that the source is spurious (most commonly because it is a sidelobe of of a nearby bright source). Low values mean the source is unlikely to be spurious. Sidelobe probabilities for this version of the catalog have been computed using an improved algorithm based on multiple voting oblique decision tree classifiers. The classifiers were trained using deep VLA fields that give reliable assessments of the reality of FIRST sources. The algorithm will be described in detail in a future paper on the final FIRST catalog; nevertheless, we still recommend checking the images. Note (4): 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 paper 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. Note on (5): 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 ∼3arcmin 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. The sky area covered is displayed in the images at http://sundog.stsci.edu/first/catalogs/ Note (6): 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; south of +04d33'21" it is elliptical, 6.4x5.4 arcsec FWHM, with the major axis running north-south. In the southern Galactic cap (RA = 21h to 3h), the elliptical beam size increases further to 6.8x5.4 arcsec south of declination -02°30'25" 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 this case. 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<2arcsec are consistent with point sources). An simple empirical estimate of the uncertainty is σ(Size) = 10arcsec (1/SNR + 1/75) where SNR is the signal-to-noise ratio defined above. Note (7): 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. Note (8): 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 a letter E through S, depending on the date of the last catalog release in which the image was modified. The Q, R and S fields are new in this catalog, while sources extracted from the E-N fields are essentially identical to those in the previous version of the catalog. The Q fields include contributions from data taken in Spring 2009; the R fields include remade grid images that were found to have instrument or processing problems; and the S fields include data taken in Spring 2011. Note (9): These columns give information on optical counterparts from the SDSS-DR8 catalog (Cat. II/306): number of matches within a fiducial radius of 8'', the separation between the FIRST source and the nearest match, the i magnitude, and a morphological classification. A value N1=-1 indicates that the FIRST source falls outside the SDSS DR8 survey area so that no SDSS data are available; a value m1=-1 indicates no valid magnitude in the SDSS-DR8 catalog. Note (10): These columns give information on optical counterparts from the 2MASS catalog (Cat. II/246): number of matches within a fiducial radius of 8'', the separation between the FIRST source and the nearest match, and the Ks magnitude.
History: The catalog file (originally catalog_12feb16.bin.gz) was copied from http://sundog.stsci.edu/first/catalogs/ on 25-Sep-2012. The preceding versions were numbered in CDS Archives: VIII/71 (2003 April 11, 811117 sources) VIII/59 (1999 July 21, 549707 sources) VIII/51 (1998 Feb 04, 437429 sources) VIII/48 (1997 April 24, 236040 sources) See http://sundog.stsci.edu/first/catalogs/history.html for the complete version history.
(End) Robert H. Becker [LLNL], Richard L. White [STScI] 25-Sep-2012
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