J/AJ/142/78 New 2.2<z<3 quasars from SDSS and UKIDSS (Wu+, 2011)
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 2011AJ....142...78W
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 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
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 03-Nov-2012