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SDSSLASQSO - Sloan Digital Sky Survey/UKIRT DSS Large Area Survey Matched Quasars Catalog

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Overview

This table contains a catalog of over 130,000 quasar candidates with near-infrared (NIR) photometric properties, with an areal coverage of approximately 1200 deg2. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the NIR YJHK bands. The authors match the ~1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS) and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133 objects have the full nine-band photometry.

The majority (~85%) of the SDSS objects were not matched simply because these were not covered by the ULAS. The positional standard deviation of the SDSS Quasar to ULAS matches is 0.1370 arcseconds in RA and 0.1314 arcseconds in Dec. The authors find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS, of |RA offset| = 0.025 arcseconds and |Dec offset| = 0.040 arcseconds; they suggest the nature of this offset to be due to the matching of catalog, rather than image, level data. Their matched catalog has a surface density of ~53 deg-2 for K <= 18.27 objects; tests using this matched catalog, along with data from the UKIDSS Deep Extragalactic Survey, imply that its limiting magnitude is i ~ 20.6. Color-redshift diagrams, for the optical and NIR, show a close agreement between this matched catalog and recent quasar color models at redshift z <~ 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors.


Catalog Bibcode

2011AJ....141..105P

References

Near-infrared photometric properties of 130,000 quasars:
an SDSS-UKIDSS-matched catalog.
    Peth M.A., Ross N.P., Schneider D.P.
   <Astron. J., 141, 105 (2011)>
   =2011AJ....141..105P    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in September 2012 based on CDS Catalog J/AJ/141/105 file table4.dat.

Parameters

Source_Number
A unique sequential identification number for each source in the catalog.

Name
The IAU-Style SDSS object designation based on its J2000.0 equatorial coordinates, e.g., 'SDSS JHHMMSS.ss+DDMMSS.s'.

SDSS_ID
The SDSS ObjID database identifier for the object

RA
The Right Ascension of the SDSS quasar candidate in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-4 degrees (0.36 arcseconds) in the original table.

Dec
The Declination of the SDSS quasar candidate in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-4 degrees (0.36 arcseconds) in the original table.

LII
The Galactic Longitude of the SDSS quasar candidate.

BII
The Galactic Latitude of the SDSS quasar candidate.

RA_Offset
The relative measurement accuracy between the SDSS and the UKIDSS positions in the RA direction, in arcseconds. These values are calculated by subtracting the positional measurement as recorded in the SDSS by the positional measurement as recorded in the UKIDSS. These angular distance values are not calculated explicitly, rather they are values reported directly from the WFCAM database.

Dec_Offset
The relative measurement accuracy between the SDSS and the UKIDSS positions in the Declination direction, in arcseconds. These values are calculated by subtracting the positional measurement as recorded in the SDSS by the positional measurement as recorded in the UKIDSS. These angular distance values are not calculated explicitly, rather they are values reported directly from the WFCAM database.

Offset
The absolute value of the offset between the UKIDSS and SDSS positions, in arcseconds

Umag
The SDSS u-band PSF magnitude in the AB system of the quasar candidate. All SDSS magnitudes have been corrected for Galactic extinction using the Schlegel et al. (1998, ApJ, 500, 525) dust maps.

Umag_Error
The error in the associated magnitude. Errors are not recalculated, but are those previously reported in Richards et al. (2009, ApJS, 180, 67; available as the HEASARC SDSSNBCKDE database table).

Gmag
The SDSS g-band PSF magnitude in the AB system of the quasar candidate. All SDSS magnitudes have been corrected for Galactic extinction using the Schlegel et al. (1998, ApJ, 500, 525) dust maps.

Gmag_Error
The error in the associated magnitude. Errors are not recalculated, but are those previously reported in Richards et al. (2009, ApJS, 180, 67; available as the HEASARC SDSSNBCKDE database table).

Rmag
The SDSS r-band PSF magnitude in the AB system of the quasar candidate. All SDSS magnitudes have been corrected for Galactic extinction using the Schlegel et al. (1998, ApJ, 500, 525) dust maps.

Rmag_Error
The error in the associated magnitude. Errors are not recalculated, but are those previously reported in Richards et al. (2009, ApJS, 180, 67; available as the HEASARC SDSSNBCKDE database table).

Imag
The SDSS i-and PSF magnitude in the AB system of the quasar candidate. All SDSS magnitudes have been corrected for Galactic extinction using the Schlegel et al. (1998, ApJ, 500, 525) dust maps.

Imag_Error
The error in the associated magnitude. Errors are not recalculated, but are those previously reported in Richards et al. (2009, ApJS, 180, 67; available as the HEASARC SDSSNBCKDE database table).

Zmag
The SDSS z-band PSF magnitude in the AB system of the quasar candidate. All SDSS magnitudes have been corrected for Galactic extinction using the Schlegel et al. (1998, ApJ, 500, 525) dust maps.

Zmag_Error
The error in the associated magnitude. Errors are not recalculated, but are those previously reported in Richards et al. (2009, ApJS, 180, 67; available as the HEASARC SDSSNBCKDE database table).

Ymag
The ULAS Y-band (1.03-micron) PSF magnitude in the Vega system of the quasar candidate. The NIR magnitude are the aperture-corrected (AperMag3) magnitudes measured by UKIDSS, which records all the flux in a 2.0 arcsecond diameter and that, for typical seeing conditions, provide the most accurate estimate of the total magnitude (Dye et al. 2006, MNRAS, 372, 1227).

Ymag_Error
The error in the associated NIR magnitude as given in the ULAS database.

Jmag
The ULAS J-band PSF magnitude in the Vega system of the quasar candidate. The NIR magnitude are the aperture-corrected (AperMag3) magnitudes measured by UKIDSS, which records all the flux in a 2.0 arcsecond diameter and that, for typical seeing conditions, provide the most accurate estimate of the total magnitude (Dye et al. 2006, MNRAS, 372, 1227). The j_1AperMag3 magnitude is reported, since the ULAS ultimately aims to have J-band imaging in two epochs.

Jmag_Error
The error in the associated NIR magnitude as given in the ULAS database.

Hmag
The ULAS H-band PSF magnitude in the Vega system of the quasar candidate. The NIR magnitude are the aperture-corrected (AperMag3) magnitudes measured by UKIDSS, which records all the flux in a 2.0 arcsecond diameter and that, for typical seeing conditions, provide the most accurate estimate of the total magnitude (Dye et al. 2006, MNRAS, 372, 1227).

Hmag_Error
The error in the associated NIR magnitude as given in the ULAS database.

Kmag
The ULAS K-band PSF magnitude in the Vega system of the quasar candidate. The NIR magnitude are the aperture-corrected (AperMag3) magnitudes measured by UKIDSS, which records all the flux in a 2.0 arcsecond diameter and that, for typical seeing conditions, provide the most accurate estimate of the total magnitude (Dye et al. 2006, MNRAS, 372, 1227).

Kmag_Error
The error in the associated NIR magnitude as given in the ULAS database.

Ymag_Depth
The nominal 5-sigma depth, md, in the Y-band at the given coordinates for a Richards et al. (2009, ApJS, 180, 67) quasar catalog member that falls within the ULAS DR3 footprint (in any one of the four NIR bands). Following Equation (5) from Dye et al. (2006, MNRAS, 372, 1227), md is the 5-sigma detection limit for a point source, defined as five times the standard deviation of the counts in an aperture, corrected for flux outside the aperture.

Jmag_Depth
The nominal 5-sigma depth, md, in the J-band at the given coordinates for a Richards et al. (2009, ApJS, 180, 67) quasar catalog member that falls within the ULAS DR3 footprint (in any one of the four NIR bands). Following Equation (5) from Dye et al. (2006, MNRAS, 372, 1227), md is the 5-sigma detection limit for a point source, defined as five times the standard deviation of the counts in an aperture, corrected for flux outside the aperture.

Hmag_Depth
The nominal 5-sigma depth, md, in the H-band at the given coordinates for a Richards et al. (2009, ApJS, 180, 67) quasar catalog member that falls within the ULAS DR3 footprint (in any one of the four NIR bands). Following Equation (5) from Dye et al. (2006, MNRAS, 372, 1227), md is the 5-sigma detection limit for a point source, defined as five times the standard deviation of the counts in an aperture, corrected for flux outside the aperture.

Kmag_Depth
The nominal 5-sigma depth, md, in the K-band at the given coordinates for a Richards et al. (2009, ApJS, 180, 67) quasar catalog member that falls within the ULAS DR3 footprint (in any one of the four NIR bands). Following Equation (5) from Dye et al. (2006, MNRAS, 372, 1227), md is the 5-sigma detection limit for a point source, defined as five times the standard deviation of the counts in an aperture, corrected for flux outside the aperture.

Phot_Redshift
The photometric redshift of the quasar candidate from Richards et al. (2009, ApJS, 180, 67). On occasion, a photometric redshift of -1 (rendered as a null value in this HEASARC table) is returned in the Richards et al. catalog; this is simply an error saying that the photo-z code failed for some, usually tractable reason (G. T. Richards 2010, private communication). This issue only affects 3574 objects out of the total 1,015,082 from the Richards et al. quasar catalog and only 242 quasars on Stripe 82. The present authors do not attempt to deal with this issue, leaving the resolution for the next version of the photometric catalog.

Phot_Redshift_Min
The lower limit for the photometric redshift of the quasar candidate from Richards et al. (2009, ApJS, 180, 67). These values should be taken with the phot_redshift_prob quantity, described below. Note that the upper and lower redshift ranges are nearly, but ultimately not, symmetric about the reported photometric redshift, and therefore should not be treated as the formal error on the photometric redshift.

Phot_Redshift_Max
The upper limit for the photometric redshift of the quasar candidate from Richards et al. (2009, ApJS, 180, 67). These values should be taken with the phot_redshift_prob quantity, described below. Note that the upper and lower redshift ranges are nearly, but ultimately not, symmetric about the reported photometric redshift, and therefore should not be treated as the formal error on the photometric redshift.

Phot_Redshift_Prob
The probability of the reported photometric redshift being in the given redshift range, with Richards et al. (2009, ApJS, 180, 67, their Section 4.6 and Figure 15), and Section 4 in the reference paper, giving further details on this quantity.

Spect_Redshift
The spectroscopic redshift of the quasar candidate from Richards et al. (2009, ApJS, 180, 67), ultimately based on matches to the SDSS DR5 quasar catalog (Schneider et al. 2007, AJ, 134, 102), the 2QZ quasar catalog (Croom et al. 2004, MNRAS, 349, 1397), the 2dF-SDSS LRG and QSO Survey (2SLAQ) quasar catalog (Croom et al. 2009, MNRAS, 392, 19), and the SDSS DR6 spectroscopic database (Adelman-McCarthy et al. 2008, ApJS, 175, 297). By design, the Richards et al. catalog does not have spectroscopic information for all of its objects. The present authors find that out of the 130,827 objects matched from Richards et al. and ULAS, 20,740 have spectroscopic redshifts as reported in Richards et al., 6,623 of which are on SDSS Stripe 82. A null value (replacing the value -1 in the original table) is given when there is no corresponding spectroscopic redshift.

Galactic_Extinction
The estimated Galactic reddening E(B-V) in the given direction as taken from Schlegel et al. (1998, ApJ, 500, 525).


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 28-Sep-2012