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SDSSNBCQSC - Sloan Digital Sky Survey NBC Quasar Candidate Catalog

HEASARC
Archive

Overview

The Nonparametric Bayes Classifier (NBC) Quasar Candidate Catalog is a catalog of 100,563 unresolved, UV-excess (UVX) quasar candidates with magnitudes to as faint as 21 in the g-band from 2099 square degrees of the Sloan Digital Sky Survey (SDSS) Data Release One (DR1) imaging data. Existing spectra of 22,737 sources reveals that 22,191 (97.6%) are quasars; accounting for the magnitude dependence of this efficiency, the authors estimate that 95,502 (95.0%) of the objects in the catalog are quasars. Such a high efficiency is unprecedented in broadband surveys of quasars. This "proof-of-concept" sample is designed to be maximally efficient, but still has 94.7% completeness to unresolved, g ~< 19.5, UVX quasars from the DR1 quasar catalog. This efficient and complete selection is the result of the application of a probability density type analysis to training sets that describe the four-dimensional color distribution of stars and spectroscopically confirmed quasars in the SDSS. Specifically, the authors use a nonparametric Bayesian classification, based on kernel density estimation, to parameterize the color distribution of astronomical sources - allowing for fast and robust classification. They further supplement the catalog by providing photometric redshifts and matches to FIRST/VLA, ROSAT, and USNO-B sources.

Much more information on the SDSS is available at the project's web site at http://www.sdss.org/.


Catalog Bibcode

2004ApJS..155..257R

References

Efficient photometric selection of quasars from the Sloan Digital Sky Survey:
100000 z<3 quasars from data release one.
    Richards G.T., Nichol R.C., Gray A.G., Brunner R.J., Lupton R.H.,
    Vanden Berk D.E., Chong S.S., Weinstein M.A., Schneider D.P.,
    Anderson S.F., Munn J.A., Harris H.C., Strauss M.A., Fan X., Gunn J.E.,
    Ivezic Z., York D.G., Brinkmann J., Moore A.W.
   <Astrophys. J. Suppl. Ser., 155, 257-269 (2004)>
   =2004ApJS..155..257R

Provenance

This database table was created by the HEASARC in August 2005 based on CDS table J/ApJS/155/257/table1.dat.

Parameters

Name
The NBC Quasar Candidate Catalog designation using the unique catalog number and the prefix '[RNG2004] ' recommended by the Dictionary of Nomenclature of Celestial Objects.

SDSS_Name
The standard SDSS designation of the object, in the format 'SDSS Jhhmmss.ss+ddmmss.s' using the sexagesimal J2000.0 coordinates.

RA
The Right Ascension of the UVX quasar candidate in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 0.1 microdegrees (0.36 milliarcseconds) in the original table.

Dec
The Declination of the UVX quasar candidate in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 0.1 microdegrees (0.36 milliarcseconds) in the original table.

LII
The Galactic Longitude of the object.

BII
The Galactic Latitude of the object.

SDSS_ID
The SDSS object identifier string, in the format 'skyVersion-run-rerun-camcol-field-id'.

Row_Pixel
The row position of the object in the field, in pixels.

Column_Pixel
The column position of the object in the field, in pixels.

Umag
The u-band magnitude of the object. All magnitudes are "asinh" point spread function (PSF) magnitudes (Lupton et al., 1999AJ....118.1406L) and uncorrected for Galactic extinction.

Gmag
The g-band magnitude of the object. All magnitudes are "asinh" point spread function (PSF) magnitudes (Lupton et al., 1999AJ....118.1406L) and uncorrected for Galactic extinction.

Rmag
The r-band magnitude of the object. All magnitudes are "asinh" point spread function (PSF) magnitudes (Lupton et al., 1999AJ....118.1406L) and uncorrected for Galactic extinction.

Imag
The i-band magnitude of the object. All magnitudes are "asinh" point spread function (PSF) magnitudes (Lupton et al., 1999AJ....118.1406L) and uncorrected for Galactic extinction.

Zmag
The z-band magnitude of the object. All magnitudes are "asinh" point spread function (PSF) magnitudes (Lupton et al., 1999AJ....118.1406L) and uncorrected for Galactic extinction.

Umag_Error
The error in the u-band magnitude.

Gmag_Error
The error in the g-band magnitude.

Rmag_Error
The error in the r-band magnitude.

Imag_Error
The error in the i-band magnitude.

Zmag_Error
The error in the z-band magnitude.

Umag_Extinction
The Galactic extinction in the u-band, in magnitudes.

Gmag_Extinction
The Galactic extinction in the g-band, in magnitudes.

Rmag_Extinction
The Galactic extinction in the r-band, in magnitudes.

Imag_Extinction
The Galactic extinction in the i-band, in magnitudes.

Zmag_Extinction
The Galactic extinction in the z-band, in magnitudes.

Quasar_Density
The kernel density estimate (KDE) computed quasar probability density for the object.

Star_Density
The kernel density estimate (KDE) computed star probability density for the object. For the final catalog, NBC-selected quasars were rejected if the stellar density exceeded 0.01.

Redshift
The photometric redshift of the object, determined by the method described in Weinstein et al., 2004ApJS..155..243W using an algorithm that minimizes the difference between the measured colors of each object and the median color of quasars as a function of redshift.

Redshift_Lower_Limit
The lower limit to the photometric redshift range.

Redshift_Upper_Limit
The upper limit to the photometric redshift range.

Redshift_Probability
The probability that the photometric redshift is within the quoted range: see Weinstein et al., 2004ApJS..155..243W for more details.

Previous_Class
The previous classification for the catalog object based a match to three spectroscopic databases: (1) the SDSS-DR1 Quasar Catalog (Schneider et al., 2003AJ....126.2579S, the HEASARC Browse table SDSSQUASAR), which includes only bona fide quasars: objects from this are labelled as 'DR1QSO'; (2) the 2QZ NGP Catalog (Croom et al., 2004MNRAS.349.1397C), which includes quasars as well as nonquasars: objects from this are labelled with '2QZ' and then the object type, e.g., '2QZNELG', '2QZQSO', etc.; and (3) "good" spectroscopic IDs from the SDSS-DR2 database (Abazajian et al., 2004AJ....128..502A), which include quasars as well as nonquasars: objects from this are labelled with 'DR2' and then the object type, e.g., 'DR2GALAXY', 'DR2QSO', etc. Matching to these 3 catalogs was done in series in the order given, such that an object will only match the first occurrence. Objects with no matches have been given the value of 'U' for unknown.

Previous_Redshift
The previous redshift for the catalog object, taken from the sources listed for the previous_class parameter.

Flux_20_cm
The 20-cm flux density, in mJy, of the radio counterpart to the catalog object. Objects were matched to the FIRST Catalog (Becker et al., 1995ApJ...450..559B, White et al., 1997ApJ...475..479W) and to the Spitzer First Look Survey (Condon et al., 2003AJ....125.2411C), if the positions agreed within 1.5 arcseconds - the same radius used for the SDSS's target selection algorithm. For FIRST radio sources, the peak 20 cm flux density is listed, whereas, for objects from Condon et al.'s deep 20 cm survey, the integrated 20 cm flux density is listed. Objects that match both radio catalogs have only their FIRST data reported (as can be discerned by their >~ 1 mJy flux densities).

RASS_Count_Rate
The ROSAT All-Sky Survey (RASS) broadband (0.1 - 2.4 keV) vignetting-corrected count rate, in ct/s , of the X-ray counterpart to the catalog object, using a 30 arcseconds matching radius. The expected number of SDSS quasar candidates superposed on unrelated RASS 30" radius X-ray error circles is about 69 or 5% of the tabulated 1304 likely SDSS/RASS positional matches.

Proper_Motion
The proper motion of the catalog object, in mas/yr. The authors matched the quasar candidates to the improved USNO-B+SDSS proper motions tabulated by Munn et al. (2004AJ....127.3034M), which is 90% complete to g ~ 19.7 using criteria specified in section 4.4.3 of the published paper. 99.5% of the spectroscopically confirmed quasars in the sample have proper motions less than 20 mas/yr. There are 799 objects with proper motions >= 20 mas/yr in the catalog, most of which are likely to be stars.


Contact Person

Questions regarding the SDSSNBCQSC database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 27-Apr-2009