J/AJ/142/78            New 2.2<z<3 quasars from SDSS and UKIDSS      (Wu+, 2011)
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Discovering the missing 2.2<z<3 quasars by combining optical variability
and optical/near-infrared colors.
    Wu X.-B., Wang R., Schmidt K.B., Bian F., Jiang L., Fan X.
   <Astron. J., 142, 78 (2011)>
   =2011AJ....142...78W
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ADC_Keywords: QSOs ; Active gal. nuclei ; Redshifts ; Photometry, infrared
Keywords: galaxies: active - quasars: emission lines - quasars: general

Abstract:
    The identification of quasars in the redshift range 2.2<z<3 is
    known to be very inefficient because the optical colors of such
    quasars are indistinguishable from those of stars. Recent studies have
    proposed using optical variability or near-infrared (near-IR) colors
    to improve the identification of the missing quasars in this redshift
    range. Here we present a case study combining both methods. We select
    a sample of 70 quasar candidates from variables in Sloan Digital Sky
    Survey (SDSS) Stripe 82, which are non-ultraviolet excess sources and
    have UKIDSS near-IR public data. They are clearly separated into two
    parts on the Y-K/g-z color-color diagram, and 59 of them meet or
    lie close to a newly proposed Y-K/g-z selection criterion for z<4
    quasars. Of these 59 sources, 44 were previously identified as quasars
    in SDSS DR7, and 35 of them are quasars at 2.2<z<3. We present
    spectroscopic observations of 14 of 15 remaining quasar candidates
    using the Bok 2.3m telescope and the MMT 6.5m telescope, and
    successfully identify all of them as new quasars at z=2.36-2.88. We
    also apply this method to a sample of 643 variable quasar candidates
    with SDSS-UKIDSS nine-band photometric data selected from 1875 new
    quasar candidates in SDSS Stripe 82 given by Butler & Bloom
    (2011AJ....141...93B) based on the time-series selections, and find
    that 188 of them are probably new quasars with photometric redshifts
    at 2.2<z<3. Our results indicate that the combination of optical
    variability and optical/near-IR colors is probably the most efficient
    way to find 2.2<z<3 quasars and is very helpful for constructing a
    complete quasar sample. We discuss its implications for ongoing and
    upcoming large optical and near-IR sky surveys.

File Summary:
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 FileName   Lrecl  Records   Explanations
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ReadMe         80        .   This file
table1.dat     63       14   Parameters of 14 new 2.2<z<3.0 quasars in S82
table2.dat     96      188   188 quasar candidates with 2.2<z<3.0 in S82
                             (SDSS Stripe 82)
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See also:
   VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
     I/314 : UKIDSS-DR8 LAS, GCS and DXS Surveys (Lawrence+ 2012)
   http://www.sdss.org : SDSS Home Page

Byte-by-byte Description of file: table1.dat
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   Bytes Format Units   Label     Explanations
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   1- 19  A19   ---     SDSS      SDSS name (JHHMMSS.ss+DDMMSS.s)
  21- 29  F9.5  deg     RAdeg     Right ascension in decimal degrees (J2000)
  31- 38  F8.5  deg     DEdeg     Declination in decimal degrees (J2000)
  40- 44  F5.2  mag     imag      SDSS i magnitude
  46- 49  F4.2  ---     zph       Photometric redshift
  51- 54  F4.2  ---     zsp       Spectrsocopic redshift
  56- 59  I4    s       tExp      Exposure time
  61- 63  A3    ---     Tel       Telescope: Bok (2.3m at Steward Observatory),
                                  or MMT (6.5m in Arizona)
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Byte-by-byte Description of file: table2.dat
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   Bytes Format Units   Label     Explanations
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   1- 12  F12.8 deg     RAdeg     Right Ascension in decimal degrees (J2000)
  14- 27 F14.11 deg     DEdeg     Declination in decimal degrees (J2000)
  29- 33  F5.3  ---     z         Photometric redshift
  35- 40  F6.3  mag     umag      SDSS u band AB magnitude
  42- 47  F6.3  mag     gmag      SDSS g band AB magnitude
  49- 54  F6.3  mag     rmag      SDSS r band AB magnitude
  56- 61  F6.3  mag     imag      SDSS i band AB magnitude
  63- 68  F6.3  mag     zmag      SDSS z band AB magnitude
  70- 75  F6.3  mag     Ymag      UKIDSS Y band Vega magnitude
  77- 82  F6.3  mag     Jmag      UKIDSS J band Vega magnitude
  84- 89  F6.3  mag     Hmag      UKIDSS H band Vega magnitude
  91- 96  F6.3  mag     Kmag      UKIDSS K band Vega magnitude
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History:
    From electronic version of the journal

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(End)                  Greg Schwarz [AAS], Patricia Vannier [CDS]    03-Nov-2012