The Physical Conditions for Massive Star Formation Dust Cont

Fifty-one dense cores associated with water masers were mapped at 350 micron. These cores are very luminous, 10^3 < Lbol/Lsun < 10^6, indicative of the formation of massive stars. Dust continuum contour maps and photometry are presented for these sources.

ALTEXedat1423min.,February1,2008

APreprinttypesetusingLTEXstyleemulateapjv.14/09/00

THEPHYSICALCONDITIONSFORMASSIVESTARFORMATION:DUST

CONTINUUMMAPSANDMODELING

KaisaE.Mueller,YancyL.Shirley,NealJ.EvansII,andHeatherR.Jacobson

DepartmentofAstronomy,TheUniversityofTexasatAustin,Austin,Texas78712–1083

mueller,yshirley,nje,hrj@astro.as.utexas.eduALTEXedat1423min.,February1,2008

arXiv:astro-ph/0207322v1 15 Jul 2002

ABSTRACT

Fifty-onedensecoresassociatedwithwatermasersweremappedat350µm.Thesecoresareveryluminous,103<Lbol/L⊙<106,indicativeoftheformationofmassivestars.Dustcontinuumcontourmaps,radialintensitypro les,andphotometryarepresentedforthesesources.Thesubmillimeterdustemissionpeakis,onaverage,nearlycoincidentwiththewatermaserposition.Thespectralenergydistributionsandnormalizedradialpro lesofdustcontinuumemissionweremodeledfor31sourcesusingaone-dimensionaldustradiativetransfercode,assumingapowerlawdensitydistributionintheenvelope,n=nf(r/rf) p.Thebest tdensitypowerlawexponent,p,rangedfrom0.75to2.5with p =1.8±0.4,similartothemeanvaluefoundbyBeutheretal.(2002)inalargesampleofmassivestarformingregions.Themeanvalueofpisalsocomparabletothatfoundinregionsformingonlylowmassstars,but nf isovertwoordersofmagnitudegreaterforthemassivecores.Themeanpisincompatiblewithalogatropicsphere(p=1),butotherstarformationmodelscannotberuledout.Di erentmassestimatesarecomparedandmeanmassesofgasanddustarereportedwithinahalf-powerradiusdeterminedfromthedustemission, log(M(<rdec)) =2.0±0.6,andwithinaradiuswherethetotaldensityexceeds104cm 3, log(M(<rn)) =2.5±0.6.Evolutionaryindicatorscommonlyusedforlowmassstarformation,suchasTbolandLbol/Lsmm,mayhavesomeutilityforregionsformingmassivestars.Additionally,forcomparisonwithextragalacticstarformationstudies,theluminositytodustmassratioiscalculatedforthesesources, Lbol/MD =1.4×104L⊙/M⊙,withamethodmostparalleltothatusedinstudiesofdistantgalaxies.Thisratioissimilartothatseeninhighredshiftstarburstgalaxies.

Subjectheadings:ISM:dust—stars:formation,high-mass—submillimeter

1.introduction

Thestudyofregionsformingmassivestarsisessen-tialtoourunderstandingofhowstarsareborn.Sincemoststarsforminclustersassociatedwithhighmassstars(e.g.,Carpenter2000),manyrecentstudieshavefocusedonbetterunderstandingthephysicalconditionsintheseregions(e.g.,vanderTaketal.2000,Sridharanetal.2002,Beutheretal.2002,Hatchelletal.2000,Walshetal.2001,Osorio,Lizano,&D’Alessio1999,Garay&Lizano1999).Thedensitydistributionintheenvelopesofregionsform-ingmassivestarsisanimportantobservationalconstraintforstarformationmodels.Thedensitydistributionisusu-allyapowerlaw(n∝r p).Forexample,McLaughlin&Pudriz’s(1997)logatropicspheremodelpredictsashallowpowerlawwithp=1inthestaticenvelope,whereasShu’s(1977)inside-outcollapsemodelforisolatedstarformationhasaninitialdensitydistributionwithp=2.

Apowerlawdensitydistributionhasbeen ttedtoobservationsoflowmassstarformingregions.Shirleyetal.(2002a)andYoungetal.(2002) ndacombined p =1.6±0.4forClass0(Andr´e,Ward-Thompson,&Barsony1993)andClassIsources(Lada&Wilking1984,Lada1987,Myers&Ladd1993,Chenetal.1995).All“er-rors”onmeanvaluesinthispaperrefertothestandarddeviationofthedistributionofvaluesaboutthemean.Shirleyetal.(2002a)andYoungetal.(2002)alsoreportthatasphericalcoreshaveshallowerpowerlaws.Iftheas-phericalcoresareleftoutoftheaverageforthelowmass

1

cores, p goesto1.8.Whilelowmasscoresarewell-studied,itisonlyrecentlythatthedensitystructureofhighmasscoreshasbeeninvestigatedforlargesamples.Forexample,vanderTaketal.(2000)foundashallowdensitystructure, p =1to1.5,forasampleof14re-gionsformingmassivestars,whileBeutheretal.(2002)reported p =1.6±0.5foralargersampleof69massivestarformingregions.

Studiesofmassivestarformingcoresalsohaveimpor-tantimplicationsforunderstandingextragalacticstarfor-mation,includingstarburstgalaxies.Thefar-infraredlu-minositytodustmassratio,L/M,isatooloftenusedinextragalacticstudiestocharacterizestarformationsinceitisproportionaltothestarformationrateperunitmass(Kennicutt1998).Tolearnifstarburstgalaxiesareform-ingstarsbymechanismssimilartothoseintheMilkyWay,butongranderscales,itisimportanttoinvestigatethestarformatione ciencyandL/MfordensegasinmoreaccessibleGalacticstarformationregionstoprovideapointofcomparisonbetweenthesemodesofstarforma-tion.

1.1.TheSample

TheobjectsinthisstudywereselectedfromthesampleofPlumeetal.(1992,1997)ofmassivestarformingcoresassociatedwithwatermasers.Table1liststhesourcesandtheirobservedproperties.Watermasersareasso-ciatedwithregionsofverydensegas(n≥1010cm 3;Elitzuretal.1989).Eachofthecoreshadbeenmapped

Fifty-one dense cores associated with water masers were mapped at 350 micron. These cores are very luminous, 10^3 < Lbol/Lsun < 10^6, indicative of the formation of massive stars. Dust continuum contour maps and photometry are presented for these sources.

2Muelleretal.

intheCSJ=5→4transition(Shirleyetal.anddetectedintheCSJ=7→6transition(TA

2002b)

>1.0K;Plumeetal.1992).3ThecriticaldensityofCSJ=5→4isnc=38.9×106cm ;however,adensity,nlineof1Keff,of2.2×106cm willproduceanobservableforagastem-peratureof10K(Evans1999).Foragastemperatureof100K,whichmaybetterdescribemassivecores,thee ec-tivecriticaldensityisevenlower,neff=6.0×104cm 3(Evans1999).Consequently,modelsconstrainedbymul-tipletransitionsareneededtodeterminedensity.Plumeetal.(1997)reported log(n) =5.9fromLVGmodelsofmultipleCStransitionsfortheregionsfromwhichoursamplewastaken.Therefore,theseobjectswereknowntocontainasigni cantamountofdensegas;however,theirm …… 此处隐藏：55238字，全部文档内容请下载后查看。喜欢就下载吧 ……