High-excitation CO in a quasar host galaxy at z=6.42

We report the detection of high excitation CO emission from the most distant quasar currently known, SDSS J114816.64+525150.3 (hereafter J1148+5251), at a redshift z=6.419. The CO (J=6-5) and (J=7-6) lines were detected using the IRAM Plateau de Bure inter

Astronomy&Astrophysicsmanuscriptno.bertoldi˙j1148(DOI:willbeinsertedbyhandlater)

February2,2008

High-excitationCOinaquasarhostgalaxyatz=6.42

F.Bertoldi1,P.Cox2,R.Neri3,C.L.Carilli4,F.Walter4,A.Omont5,A.Beelen2,

C.Henkel1,X.Fan6,MichaelA.Strauss7,K.M.Menten1

12

arXiv:astro-ph/0307408v1 23 Jul 2003

34567

Max-Planck-Institutf¨urRadioastronomie,AufdemH¨ugel69,D-53121Bonn,GermanyInstitutd’AstrophysiqueSpatiale,Universit´edeParisXI,F-91405Orsay,FranceIRAM,300ruedelaPiscine,38406St-Martin-d’H`eres,France

NationalRadioAstronomyObservatory,P.O.Box,Socorro,NM87801,USAInstitutd’AstrophysiquedeParis,CNRS&Universit´eParis6,98bisbd.Arago,75014Paris,FranceStewardObservatory,TheUniversityofArizona,TucsonAZ85721,USAPrincetonUniversityObservatory,Princeton,NJ08544,USA

Received30May2003/AcceptedJuly2003

Abstract.WereportthedetectionofhighexcitationCOemissionfromthemostdistantquasarcurrentlyknown,SDSSJ114816.64+525150.3(hereafterJ1148+5251),ataredshiftz=6.419.TheCO(J=6→5)and(J=7→6)linesweredetectedusingtheIRAMPlateaudeBureinterferometer,showingawidthof≈280kms 1.Anupper uxlimitfortheCO(J=1→0)linewasobtainedfromobservationswiththeE elsberg100-metertelescope.Assumingnogravitationalmagni cation,weestimateamoleculargasmassof≈2×1010M⊙.UsingtheCO(3→2)observationsbyWalteretal.(2003),acomparisonoftheline uxratioswithpredictionsfromalargevelocitygradientmodelsuggeststhatthegasislikelyofhighexcitation,atdensities～105cm 3andatemperature～100K.SinceinthiscasetheCOlinesappeartohavemoderateopticaldepths,thegasmustbeextendedoverafewkpc.ThegasmassdetectedinJ1148+5251canfuelstarformationattherateimpliedbythefar-infraredluminosityforlessthan10millionyears,atimecomparabletothedynamicaltimeoftheregion.Thegasmustthereforebereplenishedquickly,andmetalanddustenrichmentmustoccurfast.Thestrongdustemissionandmassive,densegasreservoiratz～6.4providefurtherevidencethatvigorousstarformationisco-evalwiththerapidgrowthofmassiveblackholesattheseearlyepochsoftheUniverse.

Keywords.galaxies:formation–galaxies:starburst–galaxies:high-redshift–quasars:emissionlines–quasars:individual:SDSSJ1148+5251–cosmology:observations

1.Introduction

Theluminousquasarsatredshiftsz>6foundintheSloanDigitalSkySurveybyFanetal.(2001,2003)provideauniqueopportunitytostudytheformationofmassiveob-jectsduringtheepochatwhichtheintergalacticmediumwasbeingreionizedbythe rstluminoussources(Beckeretal.2001;Kogutetal.2003;Cen2003).Studyingsigna-turesofstarformationintheseexceptionalobjectsisalsoofgreatinteresttotestwhetherthecorrelationbetweenthecentralblackholemassandthestellarbulgemassob-servedinlocalspheroids(Magorrianetal.1998;Gebhardtetal.2000)canbetracedtotheearlyformationstagesofquasarsandtheirhostgalaxies.

J1148+5251,ataredshiftofz=6.42(Fanetal.2003),isthemostdistantquasarknown,observedonly≈850millionyearsaftertheBigBang(weadoptH0=71kms 1Mpc 1, Λ=0.73and m=0.27–Spergel

We report the detection of high excitation CO emission from the most distant quasar currently known, SDSS J114816.64+525150.3 (hereafter J1148+5251), at a redshift z=6.419. The CO (J=6-5) and (J=7-6) lines were detected using the IRAM Plateau de Bure inter

2F.Bertoldietal.:COinaquasarhostatz=6.42

luminosityis～3000M⊙yr 1whichrequiresvastamountsofmoleculargastobemaintained.

Moleculargasinexcessof1010M⊙wasdetectedthroughtheirCOemissionin fteenz>2far-infraredul-traluminous(LFIR>1012L⊙)radiogalaxiesandquasars(e.g.,Cox,Omont,&Bertoldi2002).Atz>4,COemis-sionwasdetectedtowardsfourquasars(Omontetal.1996;Ohtaetal.1996;Guilloteauetal.1997,1999;Coxetal.2002).TheCOemissionwasresolvedinBR1202 0725(Carillietal.2002)atz=4.69,thehighestredshiftCOdetectedsofar,andPSS2322+1944atz=4.12(Carillietal.2003).TheextendednatureoftheCOprovidesthemostdirectevidenceforactivestarformationinthehostgalaxiesofdistantquasars,andindicatesthatblackholeaccretionandstar-formationarecloselyrelated.

Toexplorethegrowthofmassiveblackholesandtheirassociatedstellarpopulationsattheendofthe“darkages”,wehavesearchedforCOemissiontowardJ1148+5251.WeherereportthedetectionofCO(6→5)and(7→6)lineemission.Inaseparatestudy,Walteretal.(2003)reportthediscoveryofCO(3→2)emissionus-ingtheVeryLargeArray(VLA).

2.Observations

ObservationsoftheCO(7→6)and(6→5)emissionlinesweremadewiththeIRAMPlateaudeBureinterferome-terbetweenMarchandMay2003.Weusedthe6antennaDcon gurationwhichresultsinabeamof5.7′′×4.1′′at3.2mm.The3mmreceiversweretunedinsinglesidebandandthetypicalSSBsystemtemperatureswere≈150K.Thetotalintegrationtimewas14hoursforCO(6→5),and

22hoursforCO(7→6).ThespectraaredisplayedinFig.1,andtheimageoftheaverageddataisshowninFig.2.Withintheastrometricuncertaintiesof±0′′.3,theCOemissioncoincideswiththeopticalpositiongivenbyFanetal.(2003).Atthe5′′resolutionofourPlateaudeBureobservations,theCOemissionisunresolved,con-sistentwiththeVLACO(3→2)detection,whichisunre-solvedat1′′.5(Walteretal2003).

TheCO(6→5)and(7→6)linesaredetectedatcentroidfrequenciescorrespondingtoaredshift6.419(Table1).Withintheuncertaintiesthisagreeswiththez=6.41±0.01oftheMgiiλ2799line(Willottetal.2003)(Fig.1).TheCOredshift,whichislikelytocorrespondtothesystemicredshiftofthequasar,di erssigni cantlyfromtherangez=6.36 6.39derivedfromhighion-izationUVlines(Whiteetal.2003),whichtracehighvelocity(≥1000kms 1),blue-shiftedgasrelatedtothequasaractivity.

Nocontinuumemissionwasdetectedinourcoadded3mmdata,whichincludesobservationsatotherfrequen-cies,butexcludesthecontinuumredwardoftheCOlines,whereweaklineemissionmaybepresent.AtthepositionofJ1148+5251weobtainacontinuum uxof0.09±0.13mJy.At43GHzthecontinuumremainsundetectedwith 31±57µJy.Theseupperlimitsareconsistentwiththemeasured250GHz uxdensityof5.0±0.6mJy(Bertoldi

Fig.1.J1148+5251spectraofCO(6→5),(7→6),andtheiraverage,binnedto64,55,and55kms 1,respec-tively,fourtimestheoriginalspectralresolution.Zerove-locitycorrespondstothecentroidofthe(6→5)lineat93.206GHz.Gaussian tswithFWHM=279kms 1areshownaslightlines.

Fig.2.Velocity-integrated(±220kms 1)mapoftheav-eragedCO(6→5)and(7→6)emission.Contourstepsare0.34mJy/beam=2σ.Thecrossindicatestheopticalpo-sition.

etal.2003),ifweadoptagreybodyspectrumwithtem-perature>50Kanddustemissivity∝ν2.

We tGaussianstothelinespectrawithin±300kms 1ofthecentroid,withnobaselinesubtraction.Thebest tlinewidthsofthethreespectrashowninFig.1rangebetween280and320kms 1,similartothewidthsfoundinotherhighredshiftquasars(e.g.,Coxetal.2002).ThewidthandcentroidofthebestGaussian ttothe

We report the detection of high excitation CO emission from the most distant quasar currently known, SDSS J114816.64+525150.3 (hereafter J1148+5251), at a redshift z=6.419. The CO (J=6-5) and (J=7-6) lines were detected using the IRAM Plateau de Bure inter

F.Bertoldietal.:COinaquasarhostatz=6.423

Table1.PropertiesoftheCOlinesobservedtowardSDSSJ1148+5251

Line

νrest

[GHz]

νobs

zCO

peakint.[mJy]

vFWHM[kms 1]

ICO

[Jykms 1]

L′CO

[1010Kkms 1pc2]

LCO[108L⊙]

24

NOTE.–ForJ1148+5251,theapparentCOlineluminosityisgivenbyL′CO=3.2×10ICOνobs,theintrinsiclineluminosityLCO=4.2×106ICOνobs,intheunitsgivenabove(seeSolomonetal.1997).Upperlimitsare3σ. AdoptingthelinewidthofCO(6→5). Linewidthcorrespondstothe50MHzchannelwidthoftheVLA46.6GHzobservations.

(6→5)linewereadoptedfortheGaussian ttothelowerquality(7→6)linetodetermineits ux.TheCO(6→5)and(7→6)line uxesaredeterminedatstrongcon dencelevelsof10σand7σ,respectively.

WesearchedforCO(1→0)emissionusingtheE elsberg100-metertelescopeinMarchandApril2003

witha1.9cmHEMTreceiver(Tsys～40KonaT

scale,aperturee ciency～40%,beamwidth60′′,positionAswitchingmode).Theintegrationtimewas～50hours,

yieldingar.m.s.ofTA

～0.4mK(～0.4mJyper24kms 1).NoCO(1→0)emissionwasdetected

attheredshiftfoundforthehigherCOtransitions(Table1).

3.Discussion

ToconstrainthephysicalconditionsofthemoleculargasinJ1148+5251wecomparedtheobservedCOline uxratioswiththosepredictedbyaone-componentlargeve-locitygradient(LVG)model(Maoetal.2000).Theline uxratiosaredeterminedbythegasdensity,temperature,andtheopticaldepthintheCOlines,i.e.,thecolumndensityofCOpervelocityinterval.Thelarge uxratiobetweenthe(6→5)and(3→2)linesimpliesthatthegashasahighexcitation.ThelowerexcitationoftheJ=7levelsuggestsamoderateopticaldepth(Fig.3).

Highgasdensitiesaretypicalofthemoleculargaspresentinthenuclearregionsofnearbystarburstgalax-ies(Solomon&Downes1998).Themostextremecon-ditionssofarwerefoundinthestarburstnucleusofNGC253(Fig.3),wheretheCOexcitationissimilartothatinJ1148+5251.DetailedLVGmodelingbyBradfordetal.(2003)indicatethattheCO,13CO,andH2dataofNGC253areconsistentwithn(H2)=4.5×104cm 3andT=120K,andCOlineopticaldepthsτ<4(Fig.3).Withonlythreeline uxesandoneupperlimit,wecannotconstrainthephysicalconditionsofthegasinJ1148+5251astightly:thedatacanbe tbothwithlow-opacitymod-els,inwhichtemperatureanddensityaredegenerate,Tn1/2≈2.5×104Kcm 1.5,andwithhigh-opacitylower-excitationmodels.WiththehighexcitationtemperaturesforthegasinNGC253andJ1148+5251thecosmicback-groundtemperature(3Kand20K,respectively)doesnota ectthegasexcitationnotably.

ToinferthetotalmolecularmassfromtheCOemis-sionintheabsenceofconstraintsontheCOabundance,

Fig.3.Integratedline ux,ICO,normalizedtoCO(6→5).DiamondsshowthevaluesforJ1148+5251.Thedashedlineshowsline uxincreasingasν2,whichisexpectedforopticallythickconditions.ThesolidlinesshowLVGmodelswithTkin=120Kandn(H2)=4.5×104cm 3,withdi erentmaximumopticaldepthintheCOlines.Thedottedlineshowstheline uxdistributionobservedforthestarburstnucleusofNGC253(Bradfordetal.2003).

onetypicallyadoptsanempiricalconversionfactor,α,be-tweentheapparentCO(1→0)lineluminosityL′totalmolecularmass,MCO,andtheHdependontheCOexcitation.2.However,thisconversionmayInnearbystarburstswithmoderategasexcitation,Downes&Solomon(1998)deriveα=0.8M⊙(Kkms 1pc2) 1.Thehighexcita-tionandmoderatelineopacitiesofourone-componentLVGmodelforJ1148+5251predictaCO(1→0)line uxmuchlowerthanthatofanopticallythickdistri-bution(Fig.3).AsobservedforNGC253,itislikelythatanopticallythick,low-excitationmolecularcompo-nentaddstothelowerJlevelpopulations.Giventhisun-certainty,andsinceavalueofαforveryhighexcitationconditionsisunknown,wedonotestimatethemasson

We report the detection of high excitation CO emission from the most distant quasar currently known, SDSS J114816.64+525150.3 (hereafter J1148+5251), at a redshift z=6.419. The CO (J=6-5) and (J=7-6) lines were detected using the IRAM Plateau de Bure inter

4F.Bertoldietal.:COinaquasarhostatz=6.42

theonecomponentLVGpredictions,butextrapolateto

L′→0)=2.7×1010Kkms

1

CO(1pc2,withtheassumptionofaconstantlinebrightnesstemperature(theopticallythickcase)fromJ=1to6.Withthequotedconversionfactor,we ndMH2≈2×1010M⊙.WethenestimatethegastodustmassratioMH2/Mdust≈30,whichissimilartothevaluesfoundforlocalULIRGsandotherhighred-shiftquasars(e.g.,Guilloteauetal.1999;Coxetal.2002).Theminimumareaofthemolecularregioncanbeestimatedfromtheratiooftheobservedlinebrightnesstemperature(11mKforCO(6→5))andtheintrinsiclinebrightness,whichis23and56KintheLVGmod-elswithτ=4and1,respectively(Fig.3).Witha5′′beamthecorrespondingsourceradius(assuminguniformcoverage)is0.1–0.15′′,or560–840pc.Placing2×1010M⊙inavolumeofradius560pcgivesanaverageCOcol-umndensity1.2×1020(XCO/10 4)cm 2,whereXCOistheCOabundancerelativetoH2.IftheobservedCOlineshavemoderateopticaldepth,τ<4,theCOcol-umnis<2×1019cm 2,whichwouldeitherrequirealowCOabundance,XCO<2×10 5,oralargervolume.Consideringthelowgas-to-dustratioestimatedaboveandthehighmetalicitiesimpliedbytheopticallines(Fanetal.2003),aCOabundancemuchlowerthantheGalactic～10 4seemsunlikely.Rather,alargerradiusof～1400pcforthegasdistributioncouldaccountforthemoderateCOlineopacities.

Ifthemoleculargasformsaninclineddisk(angleirela-tivetotheskyplane)inKeplerianrotationaboutaspher-icalmass,thelinewidthandaminimumsourceradiusbetween560and1400pcyieldaminimum gravitationalmassenclosedbythediskof(2 6)×109sin2iM⊙.Forlargeinclinationanglesthismasswouldnotbemuchlargerthanthatoftheblackhole,andafactor4–10smallerthanthegasmassimpliedbythelineintensities.Thelattermayhavebeenoverestimatedgiventheapproximatenatureofourestimate;alternatively,theCOdiskinclinationisclosetotheskyplane,i～20 30deg,whichismorelikelycon-sideringthelargedustmass,andthefactthattheAGNisopticallyunobscured.

ThedetectionoflargeamountsofdensemoleculargasinJ1148+5251supportstheconjecturethatthestrongfar-infraredluminosityseenfrommanyquasarsarisesfromextendedstarformingregions,andisnotduetoheat-ingfromtheAGN(Omontetal.2001,2003;Carillietal.2001).AlthoughforJ1148+5251theemissionremainsspatiallyunresolved,thelargemassesofwarmCOareun-likelytobeheatedbytheAGNatakpcdistance.Withtheestimatedmassofmoleculargasof～2×1010M⊙starformationinJ1148+5251couldbesustainedattherate～3000M⊙yr 1impliedbythefar-infraredluminos-ityforashorttimeonly,<10millionyears.Thisiscomparabletotheestimateddutycycletimeofquasars(e.g.Wyithe&Loeb2003),andtothedynamicaltimeofthestarformingregion,whichimpliesarapidgasdeple-tionunlessthesystemcontinuestoaccretegasatahighrate.Ifthereplenishinggasisoflow-metalicity,theshort

depletiontimesuggeststhattheenrichmentwithheavyelementsanddustisrapid,whichleavesonlysupernovaeandwindsfromthemostmassivestarsaspossiblesources.

OurlowestimateforthedynamicaltoluminousmassratioexcludesthepresenceofalargestellarmasswithinthevolumeoftheCOemission.Thedurationofstarfor-mationatthepresentratecouldthereforenothavebeenmuchlongerthan107yr,unlessthestarburstdoesnotformmanylong-lived,low-massstars,inwhichcasethestarformationratewouldhavebeenoverestimatedandthedepletiontimecouldbelonger.

Thedynamicalmassisanorderofmagnitudesmallerthanthebulgemassdeducedfromthecorrelationbetweentheblackholemassandthebulgemass(orvelocitydis-persion)inlocalspheroids(Magorrianetal.1998).Thiscouldbeduetoabiasedselectionofanon-representative,brightquasar,oritcon rmsatendencyforthestellartoblackholemassratiotodecreaseathigherredshifts(Rixetal.1999),possiblyduetoself-regulatingstarformationmechanisms(Wyithe&Loeb2003).

Acknowledgements.WethanktheIRAMPlateaudeBuresta andtheE elsbergoperatorsfortheirgreatsupportintheob-servations,http://www.77cn.com.cnbesforhelpfulcomments.

References

Becker,R.H.,etal.2001,AJ,122,2850

Bertoldi,F.,Carilli,C.,Cox,P.,Fan,X.,Strauss,M.,Beelen,

A.,Omont,A.,&Zylka,R.2003,A&A,000,L00

Bradford,C.,Nikola,T.,Stacey,G.,etal.2003,ApJ,586,891Carilli,C.L.,Kohno,K.,Kawabe,etal.2002,AJ,123,1838Carilli,C.L.,BertoldiF.,Omont,A.,Cox,P.,McMahon,R.G.,

&Isaak,K.2001,AJ,122,1679

Carilli,C.L.,Lewis,G.F.,Djorgovski,S.G.,Mahabal,A.,Cox,

P.,Bertoldi,F.&Omont,A.,2003,Science,300,773Cen,R.2003,ApJ,submitted,astro-ph/0303236

Cox,P.,Omont,A.,&Bertoldi,F.2002,inInfrared&Submm

SpaceAstronomy,ed.M.Giard,EAS(EDPSciences),399Cox,P.,Omont,A.,Djorgovski,S.,etal.2002,A&A,387,406Downes,D.,&Solomon,P.1998,ApJ,507,615

Fan,X.,Narayanan,V.,Lupton,R.,etal.2001,AJ,122,2833Fan,X.,Strauss,M.,Schneider,D.,etal.2003,AJ,125,1649Gebhardt,K.,Bender,R.,etal.2000.ApJ539,L13

Guilloteau,S.,Omont,A.,McMahon,R.G.,Cox,P.,&

Petitjean,P.1997,A&A,328,L1

Guilloteau,S.,Omont,A.,Cox,P.,McMahon,R.G.,&

Petitjean,P.1999,A&A,349,363

Haiman,Z.,&Loeb,A.2001,ApJ,552,459

Kogut,A.,Spergel,D.Barnes,C.,etal.2003,ApJ,inpressMagorrian,J.,etal.1998,AJ,115,2285

Mao,R.Q.,Henkel,C.,Schulz,A.etal.2000,A&A,358,433Ohta,K.,Yamada,T.,etal.1996,Nature,382,426

Omont,A.,Petitjean,P.,Guilloteau,S.,McMahon,R.G.,

Solomon,P.M.,P´econtal,E.1996,Nature,382,428

Omont,A.,Cox,P.,Bertoldi,F.,McMahon,R.G.,Carilli,C.L.,

&Isaak,K.2001,A&A,374,371

Omont,A.,Beelen,A.,Bertoldi,F.,Cox,P.,Carilli,C.L.,et

al.2003,A&A,398,857

Rix,H.-W.,Falco,E.E.,Impey,C.,etal.2001,ASP

Conf.Ser.237:GravitationalLensing:RecentProgress,169

We report the detection of high excitation CO emission from the most distant quasar currently known, SDSS J114816.64+525150.3 (hereafter J1148+5251), at a redshift z=6.419. The CO (J=6-5) and (J=7-6) lines were detected using the IRAM Plateau de Bure inter

F.Bertoldietal.:COinaquasarhostatz=6.42

Shields,G.,Gebhardt,K.,al.2003,ApJ,583,124

Solomon,P.M.,Downes,D.,Radford,S.J.E.,&Barrett,J.W.

1997,ApJ478,144

Spergel,D.N.,Verde,L.,Peiris,H.,etal.2003,ApJ,submittedWalter,F.,Carilli,C.,Bertoldi,F.,etal.2003,NatureWhite,R.,Becker,R.,Fan,X.,Strauss,M.2003,AJ,000Wyithe,J.S.B.,&Loeb,A.2003,astro-ph/0304156

Willott,C.J.,McLure,R.J.,&Jarvis,M.2003,ApJ,587,L15

5

本文来源：https://www.bwwdw.com/article/u6um.html