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J/ApJ/728/23       GALEX UV-bright high-redshift quasars       (Worseck+, 2011)
GALEX far-ultraviolet color selection of UV-bright high-redshift quasars.
    Worseck G., Prochaska J.X.
   <Astrophys. J., 728, 23 (2011)>
   =2011ApJ...728...23W
ADC_Keywords: Photometry, ultraviolet ; Photometry, SDSS ; Redshifts ;
              QSOs ; Surveys
Keywords: diffuse radiation - intergalactic medium - quasars: absorption lines -
          surveys - techniques: photometric - ultraviolet: galaxies

Abstract:
    We study the small population of high-redshift (zem>2.7) quasars
    detected by the Galaxy Evolution Explorer(GALEX), whose far-UV
    emission is not extinguished by intervening HI Lyman limit systems. We
    correlate almost all verified zem>2.7 quasars to the GALEX GR4
    source catalog covering ∼25000deg2, yielding 304 sources detected at
    signal-to-noise ratio (S/N)>3. However, ∼50% of these are only
    detected in the GALEX NUV band, signaling the truncation of the FUV
    flux by low-redshift optically thick Lyman limit systems. We regard 52
    quasars detected at S/N>3 to be most promising for Hubble Space
    Telescope follow-up, with an additional 114 quasars if we consider
    S/N>2 detections in the FUV. Combining the statistical properties of
    HI absorbers with the Sloan Digital Sky Survey (SDSS) quasar
    luminosity function, we predict a large all-sky population of ∼200
    quasars with zem>2.7 and i≲19 that should be detectable at the HeII
    edge at m304<21. However, SDSS provides just half of the NUV-bright
    quasars that should have been detected by SDSS and GALEX. With mock
    quasar photometry we revise the SDSS quasar selection function,
    finding that SDSS systematically misses quasars with blue u-g≲2
    colors at 3≲zem≲3.5 due to overlap with the stellar locus in color
    space.

Description:
    We compiled a list of practically all known quasars at zem≥2.7
    from four quasar samples (SDSS-DR5 quasar catalog (Cat. VII/252;
    superseded by Cat. VII/260), SDSS photometric catalogs -DR6 (Cat.
    II/282) and -DR7 (Cat. II/294) and Veron-Cetty et al. 2006, Cat.
    VII/248; superseded by Cat. VII/258). We removed all misidentified
    SDSS sources and all quasar candidates without unambiguous redshifts
    from follow-up spectroscopy, but only after cross-correlating the
    initial quasar sample to the GALEX GR4 source catalog. We
    cross-correlated our initial quasar list to the available GALEX GR4
    source catalogs using a maximum match radius of 4.8" around the
    optical quasar position. The match radius approximately corresponds to
    the typical GALEX FWHM.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table3.dat        82       52  *Promising targets to search for HeII (GALEX
                             S/N>3 and (FUV-NUV)<1mag)
table4.dat        82      114  *Further quasars with potential FUV flux (GALEX
                             S/N(FUV)>2)

Note on table3.dat: Thirty-nine of the 41 zem>2.78 quasars were previously
   suggested as candidate HeII quasars by Syphers et al. (2009,
   Cat. J/ApJS/185/20).
Note on table4.dat: Seventy-six of the 87 zem>2.78 quasars were previously
   suggested as candidate HeII quasars by Syphers et al. (2009,
   Cat. J/ApJS/185/20).


See also:
 VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
 VII/258 : Quasars and Active Galactic Nuclei (13th Ed.) (Veron+ 2010)
 II/294  : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
 J/ApJS/193/28    : Galaxy survey around 20 UV-bright quasars (Prochaska+, 2011)
 J/MNRAS/399/728  : UV-bright sources behind M31 halo (Fittingoff+, 2009)
 J/AJ/137/3761    : Ultraviolet quasi-stellar objects (Bianchi+, 2009)
 J/ApJS/185/20    : Additional HeII quasar sightlines (Syphers+, 2009)
 J/ApJ/690/1181   : UV-bright quasars (Syphers+, 2009)
 J/MNRAS/383/1513 : 2MASS, SDSS and FIRST fluxes of QSOs (Labita+, 2008)
 J/AJ/133/1780    : GALEX/SDSS quasar catalog (Trammell+, 2007)
 J/ApJ/664/53     : UV photometry of GALEX QSO candidates (Atlee+, 2007)
 J/ApJS/134/35    : Large Bright Quasar Survey emission lines (Forster+, 2001)
 J/A+AS/111/169   : UV-excess quasar candidates (Moreau+, 1995)
 http://www.sdss.org/ : SDSS home page
 http://galex.stsci.edu/GR4/ : GALEX GR4/GR5 at MAST


Byte-by-byte Description of file: table[34].dat

   Bytes Format Units   Label     Explanations

   1- 16  A16   ---     Name      Object designation
  18- 19  I2    h       RAh       Optical hour of right ascension (J2000)
  21- 22  I2    min     RAm       Optical minute of right ascension (J2000)
  24- 28  F5.2  s       RAs       Optical second of right ascension (J2000)
      30  A1    ---     DE-       Optical sign of declination (J2000)
  31- 32  I2    deg     DEd       Optical degree of declination (J2000)
  34- 35  I2    arcmin  DEm       Optical arcminute of declination (J2000)
  37- 40  F4.1  arcsec  DEs       Optical arcsecond of declination (J2000)
  42- 46  F5.3  ---     zem       [2.702/5.037] Emission redshift
  48- 52  F5.2  mag     mag       [15.48/24.1] Optical magnitude in Filt
  54- 56  A3    ---     Filt      Filter (BVR, b_J or r) (1)
  58- 62  F5.2  mag     FUV       GALEX GR4 FUV (∼1350-1780Å) AB magnitude
  64- 68  F5.2  mag     NUV       ? GALEX GR4 NUV (∼1770-2830Å) AB magnitude
      70  I1    ---     Lim       [0/2] Limit flag on UV detections (2)
  72- 75  F4.1  ---     F.S/N     Signal-to-noise ration in FUV
  77- 80  F4.1  ---     N.S/N     ? Signal-to-noise ration in NUV
      82  I1    ---     Nf        [0/3] Neighbor flag (3)

Note (1): SDSS r AB magnitude if the filter is r, otherwise Vega magnitude
     in the given filter.
Note (2): GALEX limit flag as follows:
   0 = formal two-band detection,
   1 = 1σ lower limit in FUV,
   2 = 1σ lower limit in NUV.
Note (3): Neighbor flag as follows:
   0 = no SDSS source within r<5" of the quasar,
   1 = sufficiently red SDSS source within r<5" of the quasar,
   2 = quasar not imaged in SDSS DR7,
   3 = potential source confusion (Deep Imaging Survey detection).


History:
  * 31-Aug-2012: From electronic version of the journal
  * 03-Sep-2012: In table 4, correction of the sign of declination for
       SDSS J1241+2719.
(End)                                     Emmanuelle Perret [CDS]    31-Aug-2012