J/AJ/142/78ivo://CDS.VizieR/J/AJ/142/78doi:10.26093/cds/vizier.51420078CDSWu X.-B.Wang R.Schmidt K.B.Bian F.Jiang L.Fan X.2018-01-05T08:57:11Z2013-01-10T14:38:11ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frquasarsactive-galactic-nucleiredshiftedinfrared-photometryThe 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.2011AJ....142...78Whttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/142/78CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVII/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 Pagehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/142/78https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/142/78http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/142/78https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/142/78https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/142/78http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/142/78GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/142/78/table1 (Parameters of 14 new 2.2<z<3.0 quasars in S82)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/142/78/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/142/78/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/142/78/table1?GETtext/xml+votable180.050000true0.210811.166440.005555555555555556Cone search capability for table J/AJ/142/78/table2 (188 quasar candidates with 2.2<z<3.0 in S82 (SDSS Stripe 82))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/142/78/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/142/78/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/142/78/table2?GETtext/xml+votable180.050000true0.21081141.16643860.0055555555555555565/4441 4709 6/17404 17405 17407 17661 17662 17727 17745 17747 17749 17751 17752 17768 17772 17773 17778 17807 17811 17813 17814 17815 17816 17829 17830 17832 17834 17835 17836 17838 17840 17842 17858 17998 18001 18002 18003 18004 18006 18007 18008 18009 18013 18019 18021 18022 18024 18026 18027 18063 18069 18070 18071 18073 18074 18075 18081 18083 18084 18085 18089 18090 18092 18093 18098 18685 18751 18765 18766 18767 18771 18772 18774 18775 18779 18780 18781 18785 18788 18789 18794 18798 18800 18801 18831 18835 18841 18842 18843 18845 18846 18851 18852 18854 18855 18860 18861 18864 18866 18880 18881 18882 19005 19006 19028 19033 19038 19047 19048 19050 19056 19058 19137 19200 19456 19457 23140 23144 23147 23149 23181 23182 23189 23194 23204 23206 23208 23212 23233 23234 36862 368638.305533028865447e-20 6.090060298487514e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/142/78?format=asciiOpticalInfrareddefaultJ/AJ/142/78/table1Parameters of 14 new 2.2<z<3.0 quasars in S82recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSDSSSDSS name (JHHMMSS.ss+DDMMSS.s)meta.id;meta.maincharRAJ2000Right ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.mainimagSDSS i magnitudemagphot.mag;em.opt.IfloatzphPhotometric redshiftsrc.redshiftfloatzspSpectrsocopic redshiftsrc.redshiftfloattExpExposure timestime.duration;obs.exposureintTelTelescope: Bok (2.3m at Steward Observatory), or MMT (6.5m in Arizona)instr.telcharSloanDisplay the SDSS data for this quasarmeta.ref.urlcharDR7Details of the SDSS-DR7 photometry for this sourcemeta.ref.urlcharJ/AJ/142/78/table2188 quasar candidates with 2.2<z<3.0 in S82 (SDSS Stripe 82)SimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.mainzPhotometric redshiftsrc.redshiftfloatumagSDSS u band AB magnitudemagphot.mag;em.opt.UfloatgmagSDSS g band AB magnitudemagphot.mag;em.opt.BfloatrmagSDSS r band AB magnitudemagphot.mag;em.opt.RfloatimagSDSS i band AB magnitudemagphot.mag;em.opt.IfloatzmagSDSS z band AB magnitudemagphot.mag;em.opt.IfloatYmagUKIDSS Y band Vega magnitudemagphot.mag;em.IR.JfloatJmagUKIDSS J band Vega magnitudemagphot.mag;em.IR.JfloatHmagUKIDSS H band Vega magnitudemagphot.mag;em.IR.HfloatKmagUKIDSS K band Vega magnitudemagphot.mag;em.IR.KfloatSloanDisplay the SDSS data for this quasarmeta.ref.urlcharUKDisplay the UKIDSS data for this sourcemeta.ref.urlcharDR7Details of the SDSS-DR7 photometry for this sourcemeta.ref.urlchar