SDSS J0806+2006 and SDSS J1353+1138 Two New Gravitationally

We report the discoveries of two, two-image gravitationally lensed quasars selected from the Sloan Digital Sky Survey: SDSS J0806+2006 at z_s=1.540 and SDSS J1353+1138 at z_s=1.629 with image separations of 1.40" and 1.41" respectively. Spectroscopic and o

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aSDSSJ0806+2006andSDSSJ1353+1138:TwoNewGravitationallyLensedQuasarsfromtheSloanDigitalSkySurveyNaohisaInada,1MasamuneOguri,2,3RobertH.Becker,4,5RichardL.White,6MichaelD.Gregg,4,5PaulL.Schechter,7YozoKawano,8ChristopherS.Kochanek,9GordonT.Richards,10DonaldP.Schneider,11J.C.Barentine,12HowardJ.Brewington,12J.Brinkmann,12MichaelHarvanek,12S.J.Kleinman,12JurekKrzesinski,12,13DanLong,12EricH.Neilsen,Jr.,14AtsukoNitta,12StephanieA.Snedden,12andDonaldG.York15,16ABSTRACTWereportthediscoveriesoftwo,two-imagegravitationallylensedquasarsselectedfromtheSloanDigitalSkySurvey:SDSSJ0806+2006atzs=1.540

We report the discoveries of two, two-image gravitationally lensed quasars selected from the Sloan Digital Sky Survey: SDSS J0806+2006 at z_s=1.540 and SDSS J1353+1138 at z_s=1.629 with image separations of 1.40" and 1.41" respectively. Spectroscopic and o

andSDSSJ1353+1138atzs=1.629withimageseparationsof θ=1′′.40

and θ=1′′.41respectively.Spectroscopicandoptical/near-infraredimaging

follow-upobservationsshowthatthequasarimageshaveidenticalredshiftsand

possessextendedobjectsbetweentheimagesthatarelikelytobelensgalaxies

atzl 0.6inSDSSJ0806+2006andzl 0.3inSDSSJ1353+1138.The eldof

SDSSJ0806+2006containsseveralnearbygalaxiesthatmaysigni cantlyperturb

thesystem,andSDSSJ1353+1138hasanextracomponentnearitsEinstein

ringthatisprobablyaforegroundstar.Simplemassmodelswithreasonable

parametersreproducethequasarpositionsand uxesofbothsystems.

Subjectheadings:gravitationallensing—quasars:inpidual(SDSSJ080623.70+200631.9,

SDSSJ135306.35+113804.8)

1.Introduction

SincethediscoveryofQ0957+561(Walshetal.1979),about80gravitationallylensed

quasarshavebeendiscovered(Kochaneketal.2004).Lensedquasarsarenotonlyintriguing

phenomenabutalsohavebecomeindispensableastronomicaltools,includingprobesofthe

cosmologicalparametersandthestructureofgalaxies(e.g.,Refsdal1964;Kochanek1991).

Inparticular,theabundanceofgravitationallensesinawell-de nedsourcesamplecanbe

usedtoconstraindarkenergy(e.g.,Turner1990;Fukugitaetal.1990;Chaeetal.2002).

Unfortunately,thelargestexistingsurvey,theCosmicLensAll-SkySurvey(CLASS;Myers

etal.2003;Browneetal.2003),containsonly22lensedradiosources(withawell-de ned

statisticalsampleof13lenses)discoveredfrom～10,000radiosources,whichisstillinsu -

cienttoplacetightconstraintsondarkenergymodels.TheSloanDigitalSkySurvey(SDSS;

Yorketal.2000)shouldleadtoasigni cantlylargerlenssampleforattackingthedarken-

ergyproblem.SDSSisexpectedtoidentify105quasarsspectroscopically(e.g.,Schneideret

al.2005)and≈106quasarsphotometrically(e.g.,Richardsetal.2004),whichshouldlead

toasampleofover102lensedquasarsgivenastandardlensingprobabilityof10 3(Turner

etal.1984).Indeed,12newlensedquasarshavebeendiscoveredfromtheSDSSquasars

sofar(Inadaetal.2003a,b,c,2005;Johnstonetal.2003;Morganetal.2003;Pindoretal.

2004,2005;Ogurietal.2004,2005;Burlesetal.2005),inadditiontorecovering5previously

knownlensedquasars(Walshetal.1979;Weymannetal.1980;Surdejetal.1987;Badeet

al.2003;Oscozetal.1997).Wecanpresentlyconstructawell-de nedstatisticalsampleof

16lensedSDSSquasars,butthereremainmanypromisingSDSSlensedquasarcandidates

forwhichthenecessaryfollow-upobservationsareincomplete.

Inthispaper,wereportonthediscoveryoftwomoregravitationallylensedquasars,

We report the discoveries of two, two-image gravitationally lensed quasars selected from the Sloan Digital Sky Survey: SDSS J0806+2006 at z_s=1.540 and SDSS J1353+1138 at z_s=1.629 with image separations of 1.40" and 1.41" respectively. Spectroscopic and o

SDSSJ080623.70+200631.9(SDSSJ0806+2006)andSDSSJ135306.35+113804.7(SDSSJ1353+1138).

Wepresentimagingandspectroscopicfollow-upobservationswiththeUniversityofHawaii

2.2-meter(UH88)telescope,theW.M.KeckObservatory’sKeckIandIItelescopes,andthe

MagellanConsortium’sLandonClay6.5-m(LC6.5m)telescope1.Wemodelthesystemsto

checkthattheirgeometriesareconsistentwiththelensinghypothesis.

Thestructureofthispaperisasfollows.Wedescribeourlenscandidateselectionsfrom

theSDSSdatain§2.Thefollow-upobservationsandmassmodelingofSDSSJ0806+2006

andSDSSJ1353+1138arepresentedin§3and§4,respectively.We nallypresentasummary

andgiveaconclusionin§5.Throughoutthepaperweassumeacosmologicalmodelwith

thematterdensity M=0.27,cosmologicalconstant Λ=0.73,andHubbleconstant

h=H0/100kmsec 1Mpc 1=0.7(Spergeletal.2003).

2.SelectingLensedQuasarCandidatesfromtheSDSS

TheSDSSisconductingaphotometricandspectroscopicsurveyof10,000squaredegrees

oftheskyapproximatelycenteredontheNorthGalacticCapusingthededicatedwide-

eld(3 eldofview)2.5-mtelescope(Gunnetal.2005)attheApachePointObservatory

inNewMexico,USA.Photometricobservations(Gunnetal.1998;Luptonetal.1999;

Tuckeretal.2005)aremadein veoptical lters(Fukugitaetal.1996).Afterautomated

dataprocessingbythephotometricpipeline(Luptonetal.2001;Lupton2005),quasarand

galaxycandidatesareselectedbythespectroscopictargetselectionalgorithms(Eisensteinet

al.2001;Richardsetal.2002;Straussetal.2002).Spectraofthesecandidatesareobtained

accordingtothetilingalgorithmof(Blantonetal.2003)usingamulti- berspectrograph

covering3800 Ato9200 AataresolutionofR～1800.Thedataareveryhomogeneous,

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