Clumpy photon-dominated regions in Carina. I. [CI] and mid-J CO lines in two 4'x4' fields

arXiv:0711.1320v1 [astro-ph] 8 Nov 2007Astronomy&Astrophysicsmanuscriptno.7815c󰀌ESO2008

February2,2008

Clumpyphoton-dominatedregionsinCarina

I.[Ci]andmid-JCOlinesintwo4′×4′fields.

C.Kramer1,M.Cubick1,M.R¨ollig3,K.Sun1,Y.Yonekura2,M.Aravena3,F.Bensch3,F.Bertoldi3,

L.Bronfman4,M.Fujishita5,Y.Fukui5,U.U.Graf1,M.Hitschfeld1,N.Honingh1,S.Ito5,H.Jakob1,

K.Jacobs1,U.Klein3,B.-C.Koo6,J.May4,M.Miller1,Y.Miyamoto5,N.Mizuno5,T.Onishi5,Y.-S.Park6,

J.L.Pineda3,D.Rabanus1,H.Sasago5,R.Schieder1,R.Simon1,J.Stutzki1,N.Volgenau1,and

H.Yamamoto5

1KOSMA,I.PhysikalischesInstitut,Universit¨atzuK¨oln,Z¨ulpicherStraße77,D-50937K¨oln,Germany2DepartmentofPhysicalScience,OsakaPrefectureUniversity,Osaka599-8531,Japan3Argelander-Institutf¨urAstronomie,AufdemH¨ugel71,D-53121Bonn,Germany4DepartamentodeAstronom´ıa,UniversidaddeChile,Casilla36-D,Santiago,Chile5DepartmentofAstrophysics,NagoyaUniversity,Chikusa-ku,Nagoya464-8602,Japan6SeoulNationalUniversity,Seoul151-742,Korea

Received/Accepted

ABSTRACT

Context.TheCarinaregionisanexcellentastrophysicallaboratoryforstudyingthefeedbackmechanismsofnewlyborn,verymassivestarswithintheirnatalgiantmolecularclouds(GMCs)atonly2.35kpcdistance.Aims.WeuseaclumpyPDRmodeltoanalysetheobservedintensitiesofatomiccarbonandCOandtoderivetheexcitationconditionsofthegas.Methods.TheNANTEN2-4msubmillimetertelescopewasusedtomapthe[Ci]3P1−3P0,3P2−3P1andCO4–3,7–6linesintwo4′×4′regionsofCarinawheremolecularmaterialinterfaceswithradiationfromthemassivestarclusters.OneregionisthenorthernmolecularcloudnearthecompactOBclusterTr14,andthesecondregionisinthemolecularcloudsouthofηCarandTr16.Thesedatawerecombinedwith13COSESTspectra,HIRES/IRAS60µmand100µmmapsoftheFIRcontinuum,andmapsof8µmIRAC/SpitzerandMSXemission.Results.WeusedtheHIRESfar-infrareddustdatatocreateamapoftheFUVfieldheatingthegas.ThenorthernregionshowsanFUVfieldofafew103inDraineunitswhilethefieldofthesouthernregionisaboutafactor10weaker.WhiletheIRAC8µmemissionlightsupattheedgesofthemolecularclouds,COandalso[Ci]appeartotracetheH2gascolumndensity.Thenorthernregionshowsacomplexvelocityandspatialstructure,whilethesouthernregionshowsanedge-onPDRwithasingleGaussianvelocitycomponent.WeconstructedmodelsconsistingofanensembleofsmallsphericallysymmetricPDRclumpswithinthe38′′beam(0.43pc),whichfollowcanonicalpower-lawmassandmass-sizedistributions.Wefindthatanaveragelocalclumpdensityof2105cm−3isneededtoreproducetheobservedlineemissionattwoselectedinterfacepositions.Conclusions.Stationary,clumpyPDRmodelsreproducetheobservedcoolinglinesofatomiccarbonandCOattwopositionsintheCarinaNebula.

Keywords.ISM:clouds,ISM:structure,ISM:individualobjects:Carina

1.Introduction

1.1.Theimportanceofatomiccarbon

Thefinestructurelinesofatomiccarbonarestrong

coolantsoftheinterstellarmedium(ISM)throughoutthe

universe:inGalacticclouds(e.g.Jakobetal.2007),inthe

MilkyWayasawhole(Fixsenetal.1999),aswellasin2Krameretal.:Clumpyphoton-dominatedregionsinCarina

modelsofphoton-dominatedregions(PDRs)predictthat

atomiccarbonisformedinasurfacelayerbyrecombi-

nationofC+anddissociationofCO.Thisappearsto

beincontradictionwithatomiccarbonemissionwhich

isobservedevenatlargedistancesfromUVsources.The

dynamicsoftheISMmayplayadecisiverole,allowing

toexplainthedistributionof[Ci]withtimedependentchemicalmodels(Okaetal.2004;St¨orzeretal.1997).However,stationary,butclumpyPDRmodelshave

beensuccessfulin

explaininge.g.

extended[Ci]3P1−3P0and13CO2−1emissioninS140(Spaans1996;Spaans&vanDishoeck1997).InsideaclumpyPDR,

theUVradiationcanpenetratemuchdeeperthanit

wouldbepossibleinahomogeneouslayer(Boiss´e1990).

Meixner&Tielens(1993)showedthatthelineintensi-

tiesofalllinesareenhancedcomparedtoahomogeneous

modelwiththesameaveragedensity.Juvelaetal.(2001)

presentedamodeltoapplyMonteCarloradiativetransfer

calculationstotheresultsofmagnetohydrodynamiccal-

culationstoaccountforaclumpyandturbulentstructure.

Theyalsofoundthatlocaldensitycondensationsleadto

anincreasedcoolingefficiencyandreducedphotontrap-

ping.Anotherapproachistodescribeboththeturbulent

velocityfieldandthedensitystructurebytheirstatisti-

calproperties.Hegmannetal.(2007)calculateCOcool-

ingratesbasedonastochasticradiativetransfermodel,

whichaccountsfordensityandvelocityfluctuationswith

afinitecorrelationlength.

Here,westudythedistributionofatomiccarbon

andwarmCOintheCarinastarformingregionand

testclumpymodelsusingtheKOSMA-τPDRmodel

(St¨orzeretal.1996;R¨olligetal.2007)toderivetheexci-

tationconditionsofthegas.Spaansetal.modeltheinho-

mogeneousstructurewithaMonte-Carlocode,assuminga

fixedclump/interclumpdensityratioof10.Incontrast,we

assumethatallemissionanalyzedstemsfromtheclumps.

Theinfluenceoftheinterclumpmediumorahalolead-

ingtopre-shieldingofCOhasbeendiscussedbyBensch

(2006)andBenschetal.(2003),whoalsousedKOSMA-τ,

butisnotconsideredhere.Todescribetheclumpystruc-

ture,weassumethattheclumpsaredistributedfollow-

ingthecanonicalclumpmassandmass-sizedistributions

whichhavebeenfoundinmolecularclouds.

1.2.TheCarinanebula

TheCarinanebulaisaveryprominentsouthernstar-

formingregionatadistanceof2.35kpc(Smith

2006b).Thisgiantmolecularcloudwasfirstobservedby

Grabelskyetal.(1988)aspartoftheColumbiaCO1–0

surveyoftheMilkyWay.Theyderivedatotalmassof

6.7105M⊙andaneffectiveradiusof66pc.Intotal65O-

typestars,including6ofthe11O3-typestarsknownin

theMilkyWay(Smith2006a),produceastrongUVfield

andstrongstellarwindswhichinteractvigorouslywiththe

materialinthesurroundingmolecularclouds.Thishighconcentrationoftheearliest-typestarsisuniqueinthe

Galaxyandmayserveasatemplateformoreextreme

butmoredistantregionscontainingstellarsuperclus-

terslikethecentralregionsofNGC253ortheAntennae

(Bayetetal.2006;Schulzetal.2007).TheCarinanebula

extendsmorethan4squaredegreesonthesky.Itexhibits

apeculiarmorphologicalstructureonallscales.Massive

starsarebeingborninseveralregionswithinmolecu-

larcondensations,locatedmainlytothesouth-eastand

north-westoftheclusterTrumpler16,whichiscentered

atηCar,aluminousbluevariablestar.ηCarisembed-

dedintheHomunculusnebula(e.g.Smith2006a)andits

luminosityhaschangeddrasticallyandrepeatedlyinthe

pastcenturies,leadingtostrongvariationsoftheFUV

fieldimpingingonthesurroundingclouds.Itscurrentlu-

minosityof5106L⊙makesitoneofthebrightestcelestial

infraredobjects(Cox1995).Inthenorthernpartofthe

Carinanebula,thestellarpopulationisdominatedbythe

clusterTr14.Recently,Oberstetal.(2006)reportedthe

detectionofthe[Nii]lineat205µmattheradiopeakof

theCarinaIIHiiregionusingSPIFIatAST/RO.They

comparedtheirdatawith[Cii]data(Mizutanietal.2004,

2002)andconcludedthataboutathirdofthe[Cii]emis-

sionstemsfromalow-densityionizedmedium.Forare-

centoverviewoftheCarinaregion,seeSmith&Brooks

(2007).

Carinawasmappedat∼3′resolutionintheCO4–3

and[Ci]3P1−3P0linesbyZhangetal.(2001)using

theAST/RO1.7mtelescope.TheseAST/ROdatashow

large-scale[Ci]emission,coextensivewithCO4–3.

Here,wehaveusedthe4mNANTEN2telescopeto

map12COintherotationaltransitionsJ=4–3,7–6,and

[Ci]inthefinestructuretransitions3P1−3P0,and3P2−3P1(henceforth1–0and2–1)atsub-arcminuteres-

olutionsintwo4′×4′regionsofCarina(Fig.1).

OneregiontothenorthofηCarcoversthecloudinter-

facewithTr14.Thesecondregioncoversanothercloud

interfacetothesouthofηCarandTr16.

ThenorthernmolecularcloudtothewestofTr14

(Fig1)containsseveralsitesofmassivestarforma-

tion.DiffusePAH3.29µmemissionhasbeenfoundby

Rathborneetal.(2002)totracethesharpedgeofthe

cloud.PeakintensitiesattheedgetowardstheCarIHii

regionarealmost10timeshigherthanintheotherre-

gionsofCarina.CarI-Eisinteractingwiththefrontfaceof

theGMCandcreatingaPDRseenedge-on(Brooksetal.

2003;Brooksetal.2001).CarI-Wmanifestsasecond

PDRseenface-on(cf.Fig.2).

TheCO2–1mapofCox(1995)showsasharp

rimofgasdelineatingthesouthernmolecularcloud,lo-

catedsouthofηCarandtheTr16cluster.SeveralIRAS

sourcesarelocatedalongtheedge.Aprominentpeakin

PAH3.29µmemissionistheultracompactHiiregion

IRAS10430−5931(Rathborneetal.2002).