Tracing star formation in the Rosette Molecular Cloud

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Title:
Tracing star formation in the Rosette Molecular Cloud
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Ybarra, Jason E
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Doctorate ( Ph.D.)
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University of Florida
Degree Disciplines:
Astronomy
Committee Chair:
Lada, Elizabeth Anne
Committee Members:
Sarajedini, Ata
Hamann, Frederick, Iii
Detweiler, Steven L

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formation -- infrared -- molecular -- outflow -- protostar -- protostellar -- rosette -- space -- star
Astronomy -- Dissertations, Academic -- UF
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Abstract:
Most stars form in embedded clusters distributed throughout a molecular cloud. To fully understand how clusters and molecular clouds evolve over time, I used observations of the Rosette Molecular Cloud (RMC) to study the progression of star formation, the effects of environment, and the role outflows have. In order to investigate the progression of star formation, I conducted an analysis of the distributions of young stellar objects (YSOs) and the gas from which they form. Relationships between ratios of YSO evolutionary states and extinction reveal that stars form preferentially in high extinction regions and that the column density of gas rapidly decreases as the region evolves on timescales comparable to the protostar stage. The rapid removal or relocation of gas may account for the low star formation efficiencies observed in molecular clouds. The small age spread between the embedded clusters in the cloud suggests the HII region has negligible on the global star formation history of the cloud. To investigate the role outflows from forming stars have on cluster evolution, I developed a technique using mid-infrared imaging data from the Spitzer Space Telescope to detect and study the thermal structure of shocked molecular hydrogen gas. I investigated the thermal structure of a prominent outflow in the RMC and studied interactions with its immediate surroundings.  I used near-infrared molecular hydrogen observations to investigate the distribution of shocked molecular hydrogen emission throughout the cloud and find the emission appears to be more prominent in younger regions. I find strong correlations between the total measured molecular hydrogen line emission, number of protostars, and ratio of protostars to Class II objects suggesting younger clusters have more outflow activity, and that outflow activity in the RMC decreases with age. This suggests outflows play a significant role in the gas removal within the clusters and subsequently affecting cluster and molecular cloud evolution.
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In the series University of Florida Digital Collections.
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Statement of Responsibility:
by Jason E Ybarra.
Thesis:
Thesis (Ph.D.)--University of Florida, 2013.
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Adviser: Lada, Elizabeth Anne.
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RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-02-28

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TRACINGSTARFORMATIONINTHEROSETTEMOLECULARCLOUDByJASONERICYBARRAADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOLOFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENTOFTHEREQUIREMENTSFORTHEDEGREEOFDOCTOROFPHILOSOPHYUNIVERSITYOFFLORIDA2013

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2013JasonEricYbarra 2

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IdedicatethisdissertationtoJenniferMaryCamilleCainandtothememoryofmygrandfatherJesseYbarra(1926-1999) 3

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ACKNOWLEDGMENTS Therearesomanypeoplewhohavesupportedandhelpedmetogettothispoint.Thisismyattempttoacknowledgethem.Iwouldliketoacknowledgemyadvisor,ElizabethLada.ShecontinuestothinkIamabetterwriterthanIthinkIam;Throughouttheselastfewyears,thisexpectationhasdriventhreepublishedpapersandthisdissertation.IfeelIwasgivenrelativefreedom,butIalsohadtoexplainwhatIwasdoingandjustifythedirectionsIwantedtotakemyresearch.Myideaswerebothnurturedandchallenged.Withoutherguidancethisdissertationwouldnotbepossible.IwouldliketothankmyNASAGSRPadvisor,MalcolmNiedner,forencouragementandmemorableconversations,manywhichextendedbeyondsciencetotheareasoflm,culture,andfood.Iacknowledgemypreviousadvisorandcollaborator,MaryBarsony,fromwhomIlearnedtheimportanceofbeingthoroughandtheimportanceofbeingagoodscienticcitizen.Ialsoacknowledgemyundergraduateadvisor,RandyPhelps,whorstintroducedmetotheeldofstarformation.Scienceisnotdoneinavacuum,andtherefore,IthankCarlosRoman-Ziga,JonathanTan,JohnBally,CharlesLada,PhilMyers,NaibiMarinas,ScottFleming,KristaRomita,ZoltanBalog,JunfengWang,andEricFeigelsonforalltheusefuldiscussions,questions,andcomments.IalsothankmydissertationcommitteeofAtaSarajedini,FredHamann,andSteveDetweiler.Withoutfriendssuchajourneywouldnotbeasinterestingorfun.IthankAndroRios,BretvandenAkker,BrandiGartland,RamanNarayan,AmeerThompson,Mr.DaveSexton,Alejandro`RobinBanks'Rojas,JessicaGiles,RalphMayer,NickyCunning-ham,KathrynHarris,HeatherFurlong,JoshSpurgin,EmmaBickersta,KathrynCain,andJudiCain.IalsoacknowledgethesupportgivenbyRiverSaenz,HarrietTaniguchi,WilliamDeGraenried,JohnFlaherty,andtheCSUSMcNairProgram.IthankGaryBuseyforinspiration. 4

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Iwanttothankmybrother,DavidShary,whohascontinuedtobeasourceofencouragementandinspiration.Ialsoacknowledgemyparents,WinfriedandArleenBauer,forencouragingmycuriosityandappreciationofthenaturalworldasachild.Finally,Iwouldliketothankmyance,JenniferMaryCamilleCain,forherlove,support,andinnitepatience.ThisworkisbasedinpartonarchivaldataobtainedwiththeSpitzerSpaceTele-scope,whichisoperatedbytheJetPropulsionLaboratory,CaliforniaInstituteofTech-nologyunderacontractwithNASA.FinancialsupportformystudieswasprovidedbyanawardissuedbyJPL/Caltech,aFloridaSpaceGrantfellowship,andaNASAGraduateStudentResearcherProgram(GSRP)fellowshipthroughGoddardSpaceFlightCenter. 5

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TABLEOFCONTENTS page ACKNOWLEDGMENTS ................................. 4 LISTOFTABLES ..................................... 8 LISTOFFIGURES .................................... 9 ABSTRACT ........................................ 11 CHAPTER 1INTRODUCTION .................................. 13 1.1ApproachtotheProblems ........................... 13 1.2RosetteMolecularCloud ............................ 15 1.3DescriptionofChapters ............................ 15 2PROGRESSIONOFSTARFORMATIONINTHEROSETTEMOLECULARCLOUD ........................................ 18 2.1Background ................................... 18 2.2Observations .................................. 19 2.2.1SpitzerIRACobservationsanddatareduction ............ 20 2.2.2Chandraobservationsanddatareduction ............... 20 2.2.3Near-infraredphotometrydata ..................... 22 2.3Analysis ..................................... 23 2.3.1DustextinctiondistributionintheRMC ............... 23 2.3.2IdenticationofYSOs .......................... 23 2.3.3SpatialdistributionofthedierentYSOclasses ........... 26 2.3.4AgedistributionthroughYSOratios ................. 27 2.4Discussion .................................... 32 2.4.1Starformationandcolumndensity .................. 32 2.4.2Clusterproperties ............................ 35 2.4.3AgegradientsintheRMCmaincore ................. 35 2.4.4StarformationasafunctionofdistancefromNGC2244 ....... 37 2.5Conclusion .................................... 37 3SPITZERIRACDETECTIONANDANALYSISOFSHOCKEDMOLECU-LARHYDROGENEMISSION ........................... 39 3.1Background ................................... 39 3.2Calculations ................................... 40 3.3MolecularHydrogenEmissioninIRACColorSpace ............. 41 3.4Example ..................................... 44 3.5Summary .................................... 45 6

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4SPITZERANDNEAR-INFRAREDOBSERVATIONSOFANEWBI-PLOARPROTOSTELLAROUTFLOWINTHEROSETTEMOLECULARCLOUD 48 4.1Background ................................... 48 4.2ObservationsandDataReduction ....................... 49 4.2.1SpitzerIRACandMIPSdatareduction ................ 49 4.2.2Near-infraredmolecularhydrogenobservationsanddatareduction 50 4.3ResultsandAnalysis .............................. 50 4.3.1IRACcolorspaceofshockedgas .................... 52 4.3.2IRACcoloranalysisofMHO1321 ................... 56 4.3.3Outowsource .............................. 59 4.4Discussion .................................... 60 4.4.1Structureoftheoutow ......................... 60 4.4.2Deectionoftheoutow ........................ 62 4.5Conclusions ................................... 63 5MOLECULARHYDROGENEMISSIONSURVEYOFTHEROSETTEMOLEC-ULARCLOUD .................................... 66 5.1Background ................................... 66 5.2ObservationsandDataReduction ....................... 67 5.3DistinguishingBetweenShockedandUVExcitedMolecularHydrogen ... 68 5.4Results ...................................... 69 5.4.1Molecularhydrogenemissionfeatures ................. 69 5.4.2Associationofoutowactivityandembeddedclusters ........ 70 5.4.3Drivingsources ............................. 77 5.5Summary .................................... 81 6CONCLUSION .................................... 90 6.1FutureDirections ................................ 91 REFERENCES ....................................... 93 BIOGRAPHICALSKETCH ................................ 97 7

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LISTOFTABLES Table page 2-1Diskfractionandage. ................................ 37 2-2ClusterProperties. .................................. 38 2-3AssociatedCOclumps. ................................ 38 3-1FractionalcontributionofthestrongestH2linestotheIRACbands. ....... 41 3-2TemperatureestimatesofHH54. .......................... 46 4-1PositionsanduxestimatesfortheNIRH2knotsofMHO1321. ......... 63 4-2IRACcoloranalysisofH2knots. .......................... 64 5-1Outowdrivingsources. ............................... 80 5-2ListofH2emissionfeatures. ............................. 85 8

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LISTOFFIGURES Figure page 1-1.GraphicalrepresentationofYoungStellarObject(YSO)evolutionaryclasses. 14 1-2OpticalR-bandDigitizedSkySurveyimageoftheRosetteNebulaandRosetteMolecularCloud. ................................... 16 2-1Spitzer3-colorimageoftheRosetteMolecularCloud ............... 21 2-2NICESTextinctionmapoftheRosetteMolecularCloud. ............. 24 2-3Nearest-Neighbor(NNM)densitymapsoftheRMCforClassI/0,ClassII,andClassIIIsources. ................................... 28 2-4Nearest-Neighbor(NNM)densitymapsoftheRMCmaincoreregionforClassI/0andClassIIIsources. .............................. 29 2-5Ratiomaps. ...................................... 31 2-6PlotofextinctionbinversusmeanClassIItoClassIIIratio. ........... 32 2-7PlotofextinctionbinversusmeanClassI/0toClassIIratio. .......... 33 2-8Plotofestimatedageversusmeanextinction. ................... 34 3-1IRAC[3.6][4.5]vs.[4.5][5.8]color-colorplotindicatingtheregionoccupiedbyshockedH2. ...................................... 42 3-2IRACcolor-colorplotforidentiedknotsinHH54. ................ 46 3-3IRAC4.5mimageandtemperaturemapofHH54 ............... 47 4-1SpitzerIRACimagesoftheoutow. ......................... 49 4-2Near-infraredimagesoftheoutow. ......................... 52 4-3IRACcolor-colorplotindicatingtheregionoccupiedbyshockedgascomposedofH2andCOforTmax=6103K. ........................ 55 4-4IRACcolor-colorplotindicatingtheregionoccupiedbydissociativelyshockedgascomposedofH2andCO. ............................. 56 4-5TheoutowinIRACcolorspace. .......................... 58 4-6ThermalmapoftheoutowbasedoncoloranalysisoftheIRACdata. ..... 58 4-7ColumndensitymapforH2oftheoutowbasedoncoloranalysisoftheIRACdata. .......................................... 59 4-8MIPS24mimageoftheoutowsource. ..................... 61 9

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5-12MASSK-bandimageoftheRMCwithblueboxesindicatingtheregionssur-veyedintheH22.12mline. ............................ 68 5-2NIRimagesandUVexcitedH2mapofthePL01clusterregion. ......... 71 5-3NIRimagesandUVexcitedH2mapofthePL02clusterregion. ......... 72 5-4NIRimagesandUVexcitedH2mapofthePL03embeddedcluster. ....... 73 5-5NIRimagesandUVexcitedH2mapofthePL06embeddedcluster. ....... 74 5-6NIRimagesandUVexcitedH2mapofthePL07embeddedcluster. ....... 75 5-7NIRimagesandUVexcitedH2mapoftheREFL08embeddedcluster. ..... 76 5-8NIRimagesandUVexcitedH2mapofthePL04embeddedcluster. ....... 77 5-9NIRimagesandUVexcitedH2mapofthePL05embeddedcluster. ....... 78 5-10NIRimagesandUVexcitedH2mapoftheREFL09embeddedcluster. ..... 79 5-11SummedH22.12mlineemissionvs.numberofprotostarswithin1pc(2.140)oftheclustercenters. ................................. 80 5-12SummedH22.12mlineemissionvs.ClassI/0toClassIIratiowithin1pc(2.140)oftheclustercenters. ............................. 81 5-13SummedH22.12mlineemissionvs.totalluminosityofprotostarswithin1pc(2.140)oftheclustercenters. ........................... 82 5-14NIRH2andSpitzerimagesofanoutowinPL01. ................. 82 5-15NIRH2andSpitzerimagesofoutowHH871(005-010)inPL01. ........ 83 5-16NIRH2andSpitzerimagesofoutowsinREFL08. ................ 83 5-17NIRH2andSpitzerimagesofanoutowinPL03. ................. 84 5-18NIRH2andSpitzerimagesofthecenterofclusterPL07. ............. 84 10

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AbstractofDissertationPresentedtotheGraduateSchooloftheUniversityofFloridainPartialFulllmentoftheRequirementsfortheDegreeofDoctorofPhilosophyTRACINGSTARFORMATIONINTHEROSETTEMOLECULARCLOUDByJasonEricYbarraAugust2013Chair:ElizabethA.LadaMajor:AstronomyMoststarsforminembeddedclustersdistributedthroughoutamolecularcloud.Tofullyunderstandhowclustersandmolecularcloudsevolveovertime,IusedobservationsoftheRosetteMolecularCloud(RMC)tostudytheprogressionofstarformation,theeectsofenvironment,andtheroleoutowshave.Inordertoinvestigatetheprogressionofstarformation,Iconductedananalysisofthedistributionsofyoungstellarobjects(YSOs)andthegasfromwhichtheyform.RelationshipsbetweenratiosofYSOevolutionarystatesandextinctionrevealthatstarsformpreferentiallyinhighextinctionregionsandthatthecolumndensityofgasrapidlydecreasesastheregionevolvesontimescalescomparabletotheprotostarstage.Therapidremovalorrelocationofgasmayaccountforthelowstarformationecienciesobservedinmolecularclouds.ThesmallagespreadbetweentheembeddedclustersinthecloudsuggeststheHIIregionhasnegligibleontheglobalstarformationhistoryofthecloud.Toinvestigatetheroleoutowsfromformingstarshaveonclusterevolution,Idevelopedatechniqueusingmid-infraredimagingdatafromtheSpitzerSpaceTelescopetodetectandstudythethermalstructureofshockedmolecularhydrogen(H2)gas.IinvestigatedthethermalstructureofaprominentoutowintheRMCandstudiedinteractionswithitsimmediatesurroundings.Iusednear-infraredH2observationstoinvestigatethedistributionofshockedH2emissionthroughoutthecloudandndtheemissionappearstobemoreprominentin 11

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youngerregions.IndstrongcorrelationsbetweenthetotalmeasuredH2lineemission,numberofprotostars,andratioofprotostarstoClassIIobjectssuggestingyoungerclustershavemoreoutowactivity,andthatoutowactivityintheRMCdecreaseswithage.Thissuggestsoutowsplayasignicantroleinthegasremovalwithintheclustersandsubsequentlyaectingclusterandmolecularcloudevolution. 12

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CHAPTER1INTRODUCTIONMoststarsforminembeddedclusterswithingiantmolecularclouds( Lada&Lada 2003 ).Molecularcloudsarelargestructuresofmostlymoleculargaswithsizesthatrangetenstohundredsofparsecsandwithmasses1046M.Embeddedclustersarestructuresdeeplyembeddedwithinacloud,withtypicalspatialsizeslessthan1pc,andmasses1013M( Gutermuthetal. 2009 ; Lada&Lada 2003 ).Onlyasmallfractionofgaswithinthecloudsisdense,formsstars,andisassociatedwiththeclusters( Lada 1992 ).Observationsofmolecularcloudssuggestlifetimescomparabletoclusterlifetimes,onorderofafewMyr( Elmegreen 2000 ).However,theconnectionbetweenembeddedclusterevolutionandtheevolutionofthemolecularcloudisnotwellunderstood.Therearesomeimportantquestionsthatstillneedtobeanswered: Howdoesenvironmentandlocationwithinacloudaectstarformationproperties? Howdoesstarformationprogressthroughamolecularcloud? Whatroledooutowsplayintheevolutionofembeddedclustersandclouds?Answeringthesequestionsisimportantinunderstandingtheprocessesbywhichclustersandmolecularcloudsevolveovertime. 1.1ApproachtotheProblemsRegionswherestarsformareheavilyobscuredbydust.Visualextinctionprohibitsobservationsofthesedenseregionswhereclustersareevolving.However,lightatinfraredwavelengthscanpenetratefurtherintothesedustyenvironments.Forevery10magnitudesofvisualextinction,wavelengthsgreaterthan2msuerlessthan1magnitudeofextinction.Thus,inordertoprobetheseregionsofstarformation,thisstudyprimarilyusesdataobservedwithintheinfraredregime(1to350m).ThisstudymakesextensiveusageofdatafromtheSpitzerSpaceTelescopewhichduringitscryogenicphase(2003-2009)hadwavelengthcoverageof3to180m.Near-infraredobservationsareusedtomaptheextinctionandalsotostudyshockedemissionfromoutows.X-rayscanalsopenetrate 13

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thedustyclusterenvironmentsandyoungstarshappentobeveryX-rayactive.Therefore,IalsomakeuseChandraX-rayObservatorydatatoidentifyyoungstellarobjects(YSOs),especiallytheolderobjectsthatdonotdisplayinfraredexcess.Inordertounderstandhowstarformationprogressesthoughacloud,IcomparethedistributionofextinctiontodistributionofYSOs.IusetherelativeproportionofYSOsinvariousstages(Figure 1-1 )asaprobeofage,andsubsequentlyuseagegradientsasaprobeofprogression.Theprogressionofstarformationshouldmaptheevolutionofthedensegasandrevealcluesabouttheevolutionofthecloudandthetimescaleforgasremoval.Additionally,thedistributionsofYSOsandgascanrevealtheeectofenvironmentandexternalinuencessuchasnearbyHIIregions.InordertounderstandtheroleoutowsplayImeasuretheoutowactivitywithinembeddedclustersthatareinvariousevolutionarystages.Moleculargasshockedbyoutowsemitsstronglyinthero-vibrationallinesofmolecularhydrogen(H2).TheH2S(1)2.12mlineisparticularlyusefulasitisoneofthebrightestlinesandalsoresideswithintheK-bandatmosphericwindow.Iusenear-infrarednarrow-bandimaginginthe2.12mlinetocompileacensusofH2emissionfeaturesandstudytheoutowactivityintheclusters. Figure1-1 .GraphicalrepresentationofYoungStellarObject(YSO)evolutionaryclasses. 14

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1.2RosetteMolecularCloudThetargetofthisstudyistheRosetteMolecularCloud(RMC;Figure 1-2 ).TheRosetteislocatedatadistanceof1.60.2kpc,withamassof1105M,andisaknownstarformingregion( Romn-Ziga&Lada 2008 ).Thiscloudhasaideallayoutforstudyingstarformationandtheeectsofenvironment.ItisadjacenttoanexpandingHIIregiondrivenbytheopticallyrevealedclusterNGC2244.Youngembeddedstarclustersaredistributedacrossthecloudintotofourmainregionscorrespondingtodierentenvironments( Phelps&Lada 1997 ; Romn-Zigaetal. 2008 ).TherstregionistheRosetteNebula,whichcontainstheleastembeddedandoldestcluster.TheremainingcloudcanthenbeseparatedintotheionizationfrontoftheHIIregion,thecentralcorewheretheionizationfrontandthecloudareinteracting,andabackcoreofthecloudfarfromanyinteractionwiththenebula.Inanear-infraredimagingsurveyoftheRMC, Romn-Zigaetal. ( 2008 )foundevi-denceofapossibletemporalgradientacrossthecloud;Near-infraredexcessmeasurementsindicateclustersmaybeyoungerwithincreasingdistancefromnebula.Thisstudybuildsuponthisworkbytakingacloserlookatthepossibleagegradientsbyusingmid-infraredobservationstodistinguishbetweentheprotostars(ClassI/0)andmoreevolveddisksources(ClassIII).Additionally,newChandraobservationsincreasethenumberofknownolderClassIIIsourcesandthusallowacomparisonofthedierentYSOclasses. 1.3DescriptionofChaptersInChapter2,Ianalyzethedistributionsofyoungstellarobjects(YSOs)andcomparethatwiththedistributionofgastracedbyextinction.IuseobservationsfromtheSpitzerSpaceTelescopetoidentifyyoungYSOs(ClassI/0andClassII)throughtheirinfraredexcess,andIuseobservationsfromtheChandraX-rayObservatorytoidentifymoreevolvedYSOs(ClassIII)throughtheirX-rayactivity.AnextinctionmapoftheRMCismadebymeasuringthereddeningtobackgroundstarsusingJHKphotometry.Idevelopa 15

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Figure1-2 .OpticalR-bandDigitizedSkySurveyimageoftheRosetteNebulaandRosetteMolecularCloud.Reddiamondsshowthelocationsofembeddedclusters.Bluecontoursreveallocationofintegrated13COemission.DigitizedSkySurveyimagesarepro-ducedattheSpaceTelescopeScienceInstituteusingphotographicdataobtainedusingtheOschinSchmidtTelescopeonPalomarMountainandtheUKSchmidtTelescope. techniqueusingYSOratiostostudyagegradientsacrossthecloudtobetterunderstandhowstarformationhasprogressed.InChapter3,Idescribeatechniqueforidenticationandanalysisofshockedmolec-ularhydrogen(H2)usingphotometryfromSpitzerInfraRedArrayCamera(IRAC)observations.InChapter4,IuseSpitzerIRACcoloranalysisandnear-infrarednarrow-bandH2observationstostudyaparticularlybrightbi-polaroutowtracedbybrightH2emission. 16

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ThestrongemissionintheIRACbandsallowforforthemappingofthethermalstructureoftheow.Istudytheinteractionoftheoutowwithitsimmediatesurroundings.InChapter5,IsurveytheembeddedclusterregionsforshockedH2usingnear-infrarednarrow-bandobservations.IuseSpitzerIRACcolorstodistinguishbetweenshockedandUVexcitedemission.Idescribeoutowactivityasitcorrelatestoclusterevolution.InChapter6,Isummarizetheresultsofthisstudyanddiscussfuturedirections. 17

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CHAPTER2PROGRESSIONOFSTARFORMATIONINTHEROSETTEMOLECULARCLOUD 2.1BackgroundDeterminingtheeectenvironmenthasonthestarformingprocessisimperativetogainingafullunderstandingofstarformation.Moststarsforminembeddedclustersdistributedthroughoutamolecularcloud( Lada&Lada 2003 ).Theseembeddedclustersareoftensubjecttodierentenvironmentalconditionsbasedontheirphysicallocationinthecloud.TheRosetteMolecularCloud(RMC)hasaideallayoutforstudyingstarformationandtheeectsofenvironment.AtitsnortheasternendliestheRosetteNebulawhichcontainstheOBassociationNGC2244.TheRMCcontainsmanyembeddedclustersthroughoutthelengthofthecloud.Thenear-infraredstudyof Phelps&Lada ( 1997 )identied7embeddedclusters(PL01)withinthecloud.Subsequentmid-infrared,near-infrared,andX-raystudieshaverenedandaddedtothislist. Romn-Zigaetal. ( 2008 )conrmedtheNIRclustersandalsodiscoveredtwomore(REFL08-REFL09)usingthedensitydistributionsofnear-infraredexcess(NIRX)sources.WithinthePL04region, Romn-Zigaetal. ( 2008 )foundthepeakofNIRXsources(PL04a)tobespatiallycoincidentwiththeNIRnebulosity. Poultonetal. ( 2008 )foundaconcentrationofSpitzeridentiedYSOs(clusterD=PL03b)osetby4.30(2.0pc)fromthecenteroftheNIRXdistributionPL03a.Additionally,adistributionofYSOs(clusterC=PL02b)wasfoundjustsouthoftheNIRclusterPL02. Wangetal. ( 2009 )foundaclusterofX-raysourcesinthenorthernendofPL04indicatingthepresenceofapopulationofClassIIIsources.Thecenterofthisdistribution(clusterXC=PL04b)isosetfromthepeakoftheNIRX WorkinthischapterappearsinYbarraetal.2013,TheAstrophysicalJournal,Vol-ume769,Issue2,p140.ReprintedwithpermissionfromtheAmericanAstronomicalSoci-ety.2013AmericanAstronomicalSociety 18

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distributionby3.30(1.5pc).Additionally,asmalldistributionofX-raysources(XB2)wasfoundspatiallycoincidentwithMIRclusterPL02b.Theseembeddedclustersarefoundindierentenvironments.ClustersneartheOBassociationarewithintheionizationfrontoftheHIIregion.Furtherawayfromtheionizationfront,isaregionthatisassociatedwithahighconcentrationofgasandstarformation,whereitisestimatedalmosthalfofthestarformationinthecloudistakingplace( Romn-Zigaetal. 2008 ).Thisregionmayhaveexperiencedashockfrontpassingthroughit.Finallyatthebackofthecloudisaregionwheretwoembeddedclustershaveformedbeyondtheinuenceofthenebula. Romn-Zigaetal. ( 2008 )studiedtheRMCwithadeepnear-infraredJHKsurvey.IntheiranalysisofNIRexcesssourcestheyfoundthattheexcessfractionwithintheclustersincreasedwithdistanceawayfromthethecenteroftheRosetteNebula.Thissuggestedanunderlyingagesequenceinthecloudwhereclusteragedecreaseswithincreasingdistancefromthenebula.ThissequenceextendsbeyondtheinuenceoftheHIIregionanditwassuggestedthatitsoriginisfromtheformationandevolutionofthecloud.Inthisstudywetakeacloserlookatthedistributionsoftheseyoungsourcesandfocusontrackingtheprogressionofstarformationwithinthecloud. 2.2ObservationsThisstudymakesuseofdataobtainedfromtheSpitzerSpaceTelescope,theChandraX-rayObservatory,andtheFLAMINGOSinstrumentontheKPNO2.1mtelescope.Fig-ure 2-1 isaSpitzerIRAC3-colorimageoftheRMCsurveyregion.ThebluedashedlinesshowtheextentoftheFLAMINGOSJHKsurveyandtheredlinesshowtheboundariesoftheChandraX-rayobservations.Thelocationsandnamesoftheembeddedclustersareshown. 19

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2.2.1SpitzerIRACobservationsanddatareductionForthisstudyweuseIRAC3.6.0mandMIPS24mdatafromprogram3394(PI:Bonnel)availableintheSpitzerarchive.TheIRACmappingcoversatotalprojectedareaof1.40.8degrees2forallfourIRACbands.EachIRACpointinghasaeldofviewof5.1205.120with3ditherpositionsandanexposuretimeof12secondsperframe.Additionally,weobservedtheNIRclusterREFL09withIRACfromaseparateprogram40359(PI:Rieke).TheREFL09IRACobservation(=06:35:09.11=+03:41:13.7)isasinglepointingwithaeldofviewof5.1205.120,3ditherpositions,andanexposuretimeof12secondsperframe.TheIRACframeswereprocessedusingtheSpitzerScienceCenter(SSC)IRACPipelinev14.0,andmosaicswerecreatedfromthebasiccalibrateddata(BCD)framesusingacustomIDLprogram(see Gutermuthetal. ( 2008 )fordetails).TheMIPSframeswereprocessedusingtheMIPSDataAnalysisTool( Gordonetal. 2005 ).SourcedetectionandaperturephotometrywasperformusingtheIDLsoftwarepackagePhotViswhichisbasedinpartonDAOPHOT( Gutermuthetal. 2004 2008 ).TheMIPS24mframeswereprocessedusingtheMIPSDataAnalysisTool.PSFphotometrywasperformedontheMIPSdatausingtheDAOPHOTIRAFpackage. 2.2.2ChandraobservationsanddatareductionTheembeddedRosetteclustersstudiedinthispaperwereobservedwiththeImagingArrayoftheChandraAdvancedCCDImagingSpectrometer(ACIS-I; Garmireetal. ( 2003 ))onboardoftheChandraX-rayObservatory,whichhasa170170eldofviewinasinglepointing.Theseobservationsweretakenon2010December3(ObsID12388,coveringthePL03cluster),2010December10(ObsID12142,PL06),2011January14(ObsID12387,PL01),and2011January18(ObsID12386,REFL09),withnetexposuretimeof19.6ks,39.3ks,24.5ks,and34.6ks,respectively.TheysignicantlysupplementthepreviousChandracampaignoftheRosettecomplexreportedin Townsleyetal. ( 2003 )and Wangetal. ( 2010 2009 2008 )whichconsistedoffour20ksACIS-Isnapshots 20

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Figure2-1 .Spitzer3-colorimageoftheRosetteMolecularCloud[4.5m(blue),5.8m(green),24m(red)].BluedashedlinesshowtheboundariesoftheFLAMINGOSJHKsurvey( Romn-Zigaetal. 2008 ).RedlinesshowtheboundariesoftheChandraX-rayobservations( Wangetal. 2009 ,thisstudy). 21

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inJanuary2001,adeep75ksACIS-IimageinJanuary2004centeredontheO5starHD46150inNGC2244,andone20ksACIS-IpointingattheNGC2237sub-clusterin2007.AllimagesweretakeninTimedEvent,VeryFaintmode(5pixel5pixeleventislands).Wefollowthesamecustomizeddatareductiondescribedin Wangetal. ( 2008 2007 )usingtheChandraInteractiveAnalysisofObservations(CIAO, Fruscioneetal. ( 2006 );version4.3)packageprovidedbytheChandraX-rayCenter.AdetaileddescriptionoftheX-raydataanalysiswillbepresentedinaseparatepaper(Wangetal.2013,inpreparation).ForeachoftheACISelds,weextractedX-rayimagesinthe0.5keVband,andappliedthesourcedetectionalgorithmwavdetect1( Freemanetal. 2002 )witharangeofwaveletscales(from1to16pixelsinstepsofp 2)andasourcesignicancethresholdof110)]TJ /F4 7.97 Tf 6.58 0 Td[(5toproducealistofcandidatesources.X-rayeventextractionwasmadewithourcustomizedIDLscriptACISExtract2(AE; Broosetal. 2010 ).UsingtheAE-calculatedprobabilityPBthattheextractedeventsaresolelyduetoPoissonuctuationsinthelocalbackground,werejectedsourceswithPB>0.01,i.e.thosewitha1%orhigherlikelihoodofbeingabackgrounductuation.Thetrimmedsourcelistincludes431validX-raysources. 2.2.3Near-infraredphotometrydataThisstudymakesuseofphotometrydatafromtheFLAMINGOSJHKimagingsurveyoftheRMC( Romn-Zigaetal. 2008 )whichispartoftheNOAOsurveyprogram"TowardaCompleteNear-InfraredSpectroscopicandImagingSurveyofGiantMolecularClouds"(PI:E.A.Lada).ThecompletenesslimitsforthesurveyareJ=17.25,H=18.00,andK=18.50. 1 http://cxc.harvard.edu/ciao/threads/wavdetect/ 2 http://www.astro.psu.edu/xray/docs/TARA/ae_users_guide.html 22

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2.3Analysis 2.3.1DustextinctiondistributionintheRMCAdustextinctionmapwasmadewiththeNICESTalgorithm( Lombardi 2009 )ontheFLAMINGOSphotometrycatalog.WeremovedClassI/0andClassIIsourcesfromthecatalogasthosesourceshavelargeintrinsicredcolorsandtendtobiasthemapnearthecentersofclusters.Theextinctionisestimatedtowardbackgroundsourcesbycom-paringthesourceNIRcolorswiththeintrinsiccolordistributionmeasuredfromanearbyextinction-freecontrolregion.ThecontroleldislocatedatasimilargalacticlatitudeastheRMCandwasselectedfromanIRAS25mmapasbeingdevoidofdustthermalemission(see Romn-Zigaetal. 2008 ,Figure2).Spatialsmoothingisthenappliedtotheextinctionvaluestocreatetheextinctionmap.Thesmoothingcreatesamapoftheweightedmeanasafunctionofpositiononthesky.TheweightingfunctioniscomposedofaGaussianwhichweighstheindividualextinctionmeasurementsbasedonangulardistancefromthecenterofthemappointplusacorrectiontermwhichcompensatesforthebiasduetothelownumbersofbackgroundsourcesathighextinctions.InthecaseoftheRMC,theoptimalGaussianwidthwasfoundtobe9000.Thisiscapableofresolvingcolumndensitystructuresofthemolecularcloudwithprojectedsizesofabout0.5.0pc.Figure 2-2 showstheextinctionmapoftheRMC.ThecontourlevelsindicateAV=8,10,12,14,16,20mag.Thelocationsoftheembeddedclustersareindicated.Comparisonofthelocationoftheembeddedclusterswiththeextinctiondistributionsuggestacorrespondencebetweenstarformationwiththehighestextinctionregionsofthecloud. 2.3.2IdenticationofYSOsSpitzerandChandraACISdatawereusedtoidentifyYoungStellarObjects(YSOs)intheRosetteMolecularCloud.InordertoselecttheClassI/0andClassIIsources,weemploythecolorcutsof Gutermuthetal. ( 2008 )and Kryukovaetal. ( 2012 )toourSpitzercatalog.ForobjectswhichhaveIRAC(3.6m,4.5m,5.8m,8.0m)andMIPS24m 23

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Figure2-2 .NICESTextinctionmapoftheRosetteMolecularCloud.Thecontoursrep-resentextinctionlevelsAV=8,10,12,14,16,20mag.Locationofembeddedclustersareindicated. detections,weidentifyClassI/0sourcesusingthefollowingcriteria: [4:5])]TJ /F6 11.955 Tf 11.96 0 Td[([5:8]>1or[4:5])]TJ /F6 11.955 Tf 11.95 0 Td[([5:8]>0:7and[3:6])]TJ /F6 11.955 Tf 11.95 0 Td[([4:5]>0:7 24

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and[4:5])]TJ /F6 11.955 Tf 11.96 0 Td[([24]>4:7FromtheremainingcatalogweselectClassIIsourcesthathaveallofthefollowingcriteria: [4:5])]TJ /F6 11.955 Tf 11.95 0 Td[([8:0]>0:5[3:6])]TJ /F6 11.955 Tf 11.96 0 Td[([5:8]>0:35[3:6])]TJ /F6 11.955 Tf 11.96 0 Td[([5:8]3:5([4:5])]TJ /F6 11.955 Tf 11.96 0 Td[([8:0]))]TJ /F6 11.955 Tf 11.95 0 Td[(1:75TheGutermuth[4.5][5.8]colorcutthatdistinguishesbetweenClassI/0andClassIIsourcesisparticularlyusefulastheextinctioncurveisrelativelyatinthatwavelengthrangeandthusthecolorcutisinsensitivetoextinction.ForsourceswithoutanIRAC4.5mdetection,weselectClassI/0sourcesby[5:8])]TJ /F6 11.955 Tf 11.96 0 Td[([24]>4:5and[24]<6andforClassIIsources[3:6])]TJ /F6 11.955 Tf 11.95 0 Td[([5:8]<0:35and2:0<[5:8])]TJ /F6 11.955 Tf 11.95 0 Td[([24]4:5ForobjectsthatdonothaveaMIPS24mdetection,weusethepreviousIRACcolorcutsforobjectswitha[4.5][5.8]colorandtheadditionalrequirementof[5:8])]TJ /F6 11.955 Tf 11.96 0 Td[([8:0]<1inordertolteroutAGNandPAHgalaxies.ClassIIIsourcesdonotdisplaysignicantinfraredexcessandthusneedtobeidentiedanotherway.Fortunately,YSOsareknowntoemitX-raysatlevelsthatcanrangemanyordersofmagnitudeabovemainsequencestars( Feigelsonetal. 2007 ; Preibischetal. 2005 ).Thus,X-rayobservationscanecientlyidentifyYSOsinmolecularclouds.ClassIIIcandidatesourceswereselectedfromourChandraACISobservationsand 25

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thepreviouslypublishedX-raycatalogof Wangetal. ( 2009 ).SourceswithcolorsofClassI/0orClassIIobjectswerethenremovedtocreateacatalogofClassIIIsources.Inordertodealwithextragalacticcontaminantsinoursourceslist,wealsoremovedsourcesthatdidnothaveaNIRcounterpartintheFLAMINGOScatalog.InouranalysisoftheX-rayproperties,wefoundthatthesourceswithoutaNIRcounterparthadanaveragehardnessratioconsistentwithextragalacticsources(Wangetal.,inpreparation). 2.3.3SpatialdistributionofthedierentYSOclassesByanalyzingthedistributionsofYSOclassesseparatelyonecanprobetheevolutionofstarformingregions.ThedierentYSOclassesrepresentdierentevolutionarystages,withClass0andIsourcesrepresentingtheyoungestsourcesstillembeddedintheirenvelopes,ClassIIsourcesarealaterstageofsourcesstillaccretingmaterialfromtheirdisks,andClassIIIsourcesaredisklesspre-mainsequencestars.Weemployedthek-nearestneighbor(k-NN)densityestimationalgorithm,oftenreferredtoasthenearestneighbormethod(NNM),toanalyzethestructuresanddistri-butionsoftheYSOclasses.Thismethodallowsustomapthedensitydistributionsandsubsequentlyidentifyregionsofclustering( Casertano&Hut 1985 ).Thealgorithmmea-suresthedistance,Dk,betweenasourcepointanditskthnearestneighborandestimatesthelocalstellarnumberdensityask=(k)]TJ /F6 11.955 Tf 12.34 0 Td[(1)=D2k.FortheClassI/0objectsweusedak=5,andfortheClassIIandClassIIIsourcesweusedk=10.Usingkvalueslargerthanonehastheadvantageoflesseningtheinuencepossiblenon-membersoftheset,e.g.backgroundgalaxies,haveonthelocaldensityestimate( Ferreira 2009 ).ThisisimportantwhenusingSpitzerdataasmanybackgroundgalaxieshavecolorsthataresimilartothoseofYSOsinboththenear-andmid-infrared( Fosteretal. 2008 ).Figure 2-3 presentstheNNMdensitymapsoftheClassI/0,ClassII,andClassIIIsourcesintheRMC.Thedashedlinesshowthespatialboundariesofthesurveydatausedtoidentifythesources.Theembeddedclustersarespatiallycoincidentwiththehighstellardensityregionsinthemaps.UsingtheNNMmapsoftheClassIIandClassIII 26

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sources,wehaveidentiedanewcluster(PL06b).ThemapsrevealthatthedierentYSOclassescanhaveverydierentspatialdistributions.ForexampletheClassI/0andClassIIIconcentrationsappeartobeseparatewhiletheClassIIsourcesappearmorewidespread.Thisisespeciallyevidentinthecentralregionofthecloud.Figure 2-4 showstheNNMdensitymapsofthecentralregionfortheClassI/0andClassIIIsources.AhighdensityofClassI/0sourcesisfoundinthecenterofthisregionandisspatiallycoincidentwiththehighestextinction.IncontrasttheolderClassIIIsourcesarefoundprimarilyaroundtheperimeteronnorthandeastsidesofthecentralregion.ClassIIsourcesarefoundthroughoutthecentralregion.Bynumbers,theClassIIsourcesdominatethecloud.ThedierentdensitydistributionoftheYSOclassesinthecentralregionsuggestaprogressionofstarformationfromtheouternorthandeastsectionstowardsthecentral. 2.3.4AgedistributionthroughYSOratiosInordertostudytheprogressionofstarformationintheRMC,weinvestigatehowtheratiosbetweendierentYSOclasseschangethroughoutthecloud.Astimeprogresses,ClassI/0sourceswilllosetheirenvelopesandevolveintoClassIIsources.BecausethelifetimeoftheClassI/0phaseislessthantheClassIIphase,theratioofClassI/0toClassIIsourcesshoulddecreasewiththeageoftheregion(cf. Myers 2012 ).Similarly,astimeprogresses,ClassIIsourceswilllosetheirdisksandevolveintoClassIIIsources.Diskfractionsinclustershaveanempiricalrelationshipwithage( Haischetal. 2001 ).FromdierentSpitzerIRACstudiesofyoungclusters,theaveragediskfractionsatdierentclusteragesare75%at1Myr,50%at2Myr,20%at5Myr,and5%at10Myr( Williams&Cieza 2011 ).Thus,theClassIItoClassIIIratiowithinaregionwillalsodecreasewithage(Table 2-1 ).ThisrelationshipbetweentheClassIItoClassIIIratioandageallowsustoprobeageprogressionswithinthecloud.Weconstructedratiomapsbyestimatingtheratioofthenumberofoneclassofsources,N1,tothatofanother,N2,(e.g.ClassI/0toClassII)withinaprojectedregionoftheskyacrossagrid.Wechosethesizeoftheregionbytryingtominimizeboth 27

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Figure2-3 .Nearest-Neighbor(NNM)densitymapsoftheRMCforClassI/0,ClassII,andClassIIIsources.Thedensitycontoursare=2.6,4.6,7.7,12.8starspc)]TJ /F4 7.97 Tf 6.59 0 Td[(2.ThebackgroundcontoursareAV=8,10,12,14,16,20mag.DottedlinesinthersttwopanelsshowthecoverageoftheSpitzerobservationsandthedottedlinesinthelastpanelshowthecoverageoftheChandraobservations. 28

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Figure2-4 .Nearest-Neighbor(NNM)densitymapsoftheRMCmaincoreregionforClassI/0andClassIIIsources.Thedensitycontoursare=2.6,4.6,7.7,12.8starspc)]TJ /F4 7.97 Tf 6.59 0 Td[(2.ThebackgroundcontoursareAV=8,10,12,14,16,20mag. resolutionanduncertainty.Theprobabilitydensityfunctionoftheratio,R,isp(RjN1;N2)=RN1(N1+N2+1)! (R+1)N1+N2+2N1!N2!assumingauniformpriorfortheratio( Jinetal. 2006 ).Weusetheexpectationvalueoftheratioasourestimator,^R=N1+1 N2; 29

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withvariance,2R=(N1+1)(N1+N2+1) N22(N2)]TJ /F6 11.955 Tf 11.95 0 Td[(1)Ineachpointonthegrid,foranon-zeroratiovalue,werequireR=^R0.50.FortheClassI/0toClassIIratiowechoseacircularregionwithradius1.1pcandfortheClassIItoClassIIIratioacircularregionwithradius1.4pc.TheradiusfortheClassIItoClassIIIratioislargerbecausethemagnitudecuts(seenextparagraph)reducethenumberofsources.Theregionsaresampledacrossthegridatintervalsofone-thirdtheregionradius.Thecreatedratiomapprovidesavisualrepresentationofagegradientsandcanthenmaptheprogressionofstarformation.InordertocompareClassIIandClassIIIsourcesitisnecessarytomakesurethesamplesareuniformandunbiased( Gutermuthetal. 2004 ).WerstrestrictthesamplestosourceswhicharedetectedintheFLAMINGOSJHKsurvey.WeestimatetheClassIIsampleiscompletetoH=15andtheClassIIIsampletobecompletetoH=14.WeusetheH-bandluminosityastheemissionfromdisksatthiswavelengthisnegligible.Wede-reddenoursamplestoa2Myrisochrone( Baraeetal. 1998 )andlimitthesamplestoH14,makingthesamplescompletetothesamedepthacrossthecloud.Figure 2-5 showsthetworatiomaps,theClassIItoClassIIIontheleftandtheClassI/0toClassIIontheright.Thesemapsareover-plottedontopoftheextinctioncontours.FortheClassIItoClassIIIratio,thecontourlevelsareRII:III=0.5,1.0,2.0,3.0.FortheClassI/0toClassIIratio,thecontourlevelsareRI:II=0.1,0.3,0.4,0.5.Visualinspectionofthemapssuggestacorrelationbetweentheratiosandextinction,wherehigherratiovaluesarespatiallycorrelatedwithhigherextinction.Tofurtherinvestigatethecorrelationbetweentheseratiosandextinctionwealsodeterminetheaverageextinctionineachregion.Webinnedtheregionsbyextinctioninto1magbinsandcalculatedtheweightedmeanratioineachbin.Figure 2-6 presentsaplotofextinctionbinversusmeanratioofClassIItoClassIIIsources.Thegureshowsthattheratioincreasesmonotonicallywithextinction.Theplotcanbettedwithashallow 30

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Figure2-5 .Ratiomaps.A)ClassIItoClassIIIratiomap.ThecontourlevelsareRII:III=0.5,1.0,2.0,3.0.B)ClassI/0toClassIIratiomap.ThecontourlevelsareRI:II=0.1,0.3,0.4,0.5,0.7.ThebackgroundcontoursareAV=8,10,12,14,16.DottedlinesshowthecoverageoftheSpitzerobservationsanddashdottedlinesshowthecoverageoftheChandraobservations. lineartforAV<13mag,andasteeperlineartforAV>13mag.Thus,decreasingageisrelatedtoincreasingextinction.Figure 2-7 showstheextinctionbinversusmeanClassI/0toClassIIratio.Athighextinctions,AV>17mag,theClassI/0toClassIIratioalsosteeplyincreaseswithextinction.However,thisratioappearsatfortheextinctionrangeAV=8mag.ToinvestigatethisfurtherwelookatthecontributionstothegraphfromthemaincoreandclusterPL07separately(Figure 2-7 B&C).Wendthatforthemaincoreofthecloud,wheremostofthestarformationistakingplace,theratiohasapositivemonotonicrelationwithextinction.ClusterPL07regionisdierent;Itappearstohavearelativelyatrelationshipbetweenratioandextinction,withapossibleincreaseatAV=7mag.ThereisasmallosetbetweentheextinctionpeakandClassI/0densitypeak;whichsuggestsarecentexpulsionofgasfromthecenterofPL07.Forthecloudasawhole,themeanratiosbetweentheClassI/0andClassIIsourceshaveasmall 31

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Figure2-6 .PlotofextinctionbinversusmeanClassIItoClassIIIratio. range(0.20.60)whichmaycorrespondtoanarrowrangeofagesorperhapsevidenceforcontinuousstarformation.Therelationshipsbetweenthetworatiosandextinctionrevealatrendofdecreasingagewithincreasingextinction.Thisimpliesthatstarsmaybepreferentiallyforminginthehighestextinctionpartsofthemolecularcloud. 2.4Discussion 2.4.1StarformationandcolumndensityTheClassIItoClassIIIratiomaptracesregionswithestimatedagesof0.5Myr,andtheseregionsarespatiallycoincidentwithextinctionvaluesofAV=4mag.Using 32

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Figure2-7 .PlotofextinctionbinversusmeanClassI/0toClassIIratio. theempiricalrelationshipbetweendiskfractionandclusterage,wecantapowerlawrelationtotheClassIItoClassIIIratioandage.Thenwecandirectlystudytherelationbetweenageandextinction.Figure 2-8 showsaplotofestimatedageversusextinction.TheplotsuggeststhatthecolumndensityofgasdecreaseexponentiallywithtimeaboveAV=5mag,withahalf-life,t1=2=0.4Myr.Weestimatetheaveragerateatwhichthecolumndensityofgasdecreasesas_10)]TJ /F4 7.97 Tf 6.59 0 Td[(4Myr)]TJ /F4 7.97 Tf 6.58 0 Td[(1pc)]TJ /F4 7.97 Tf 6.59 0 Td[(2whichisoveranorderofmagnitudelargerthanthestarformationratemeasuredinnearbymolecularclouds( Evansetal. 2009 ; Lada&Lada 2003 ).Thusmostofthisgasisnotremovedthroughformationofstarsandispossiblybeingrelocatedtootherregions 33

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Figure2-8 .Plotofestimatedageversusmeanextinction.TheageisestimatedfromtheClassIItoClassIIIratio.Thereddottedlineshowstheexponentialtwithhalf-life,t1=2=0.4My,aboveAV=5mag. ofthecloud.Thisisconsistentwiththestudyofnearbymolecularcloudsby Ladaetal. ( 2010 )whichdemonstratedthatstarformationonthescaleoffewMyrhasanegligibleeectonthetotalmassofthecloud.IntheRMCmaincore,wendasimilarrelationshipbetweentheClassI/0toClassIIratioandextinction.Thissuggeststhatstarformationoccurspreferentiallyinhighextinctionregions.Additionally,wendthatoverhalfoftheclustered(1:3starspc)]TJ /F4 7.97 Tf 6.58 0 Td[(2)ClassI/0sourcesarefoundatAV>15magandallofthematAV>7.5mag.Thistooisconsistentwiththestudyofnearbymolecularcloudsby Ladaetal. 34

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( 2010 )thatfoundanextinctionthresholdofAV7mag,abovewhichthestarformationratewasproportionaltothemassofthecloudmeasuredabovethatthreshold. 2.4.2ClusterpropertiesTherelationshipbetweenstarformationandcolumndensitymayhaveconsequencesfortheformationandevolutionofclusters.Table 2-2 showsthepropertiesandYSOcontentoftheclusters.Thestellarcontentismeasuredwithina1parsec(2.140)radiusofthelistedclustercenter.MostoftheembeddedclustersintheRMChaveaClassIItoClassIIIratio,RII:III,between1and2.TheweightedmeanratioofalltheembeddedclustersisRII:III=1:20:2,suggestingthatmostoftheclustersstartedformingaroundthesametime.Thereisagroupofclusterswithratiossuggestingamorerecentepisodeofstarformation,havingRII:III>3.0.ThisgroupincludesclustersPL2a,PL02b,PL03b,andREFL09.TheseclustershoweverdonotappeartohaveasignicantClassI/0population.Thissuggeststhatthestarformationintheseclustersismorecoeval.TheclusterREFL08appearstohavethemostrecentepisodeofstarformation.ThisclusterhasClassI/0sourcesconcentratedindenselamentarystructuresseeninextinction.IthasthehighestratioofClassIItoClassIIIsourceswhichisconsistentwithanagelessthan1Myr.OurX-rayobservationsdonotcoverembeddedclusterPL07.ThisclusterhasthesecondhighestconcentrationofyoungClassI/0objects.However,withoutknowledgeofitsClassIIIcontent,anageestimateforthisregionisnotpossible.Althoughtherearesomedierencesbetweentheclusters,theagespreadoftheseclustersisnonethelesssmall.TheagesinferredfromtheYSOratiosformostoftheclustersarebetween1to3Myrs. 2.4.3AgegradientsintheRMCmaincoreTheRMCmaincoreiscomposedofclustersPL04(a&b),PL05,andREFL08.EachoftheclustersisassociatedwithaCOclumpidentiedin Williamsetal. ( 1995 )COsurveyoftheRMC(Table 2-3 ).Thesethreeclustersarecharacterizedbyhavingmore 35

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YSOsthantheotherclustersinthecloud,whichisconsistentwiththestudyby Romn-Zigaetal. ( 2008 )whereitisestimatedthathalfofthestarformationinthewholecloudhappensinthisregion.TheREFL08sub-regionhasthehighestdensityofprotostarsandisspatiallycoin-cidentwiththegassurfacedensitypeak.ItsratioofClassI/0toClassIIsourcesanditsdearthofClassIIIsourcessuggesttheageofthisregiontobelessthan1Myr. Hen-nemannetal. ( 2010 )usingHerschelobservationsfound27protostarsinthisregion,7ofwhichwereclassiedasveryyoungClass0candidates.ThisregionappearslamentaryintheMIRSpitzerimageswiththemainlamentrunningnorthtosouth.ThesouthernendofthemainlamentiscoincidentwiththecenterofNIRclusterREFL08andisattheintersectionoftwosmallerlaments.Thisregionappearstobetheyoungestregionofthecloud.ClusterPL04islocatednorthofREFL08,whilePL05islocatedtotheeast.Bothclusters,PL04andPL05,appeartobeolderwithClassIItoClassIIIratiosconsistentwithages1Myrs.TheagegradientacrossthisregionasawholesuggeststhatstarformationbeganinclustersPL04andPL05rst,followedbystarformationinREFL08asamorerecentevent.BasedontheYSOcontent,weestimatetheagedierenceacrosstheregiontobeabout1Myr.ItispossiblethatstarformationfeedbackfromclustersPL04aandPL05pushedthegasintoitspresentstateandthustriggeredtheformationofREFL08.Alternatively,theformationofclusterREFL08maynothavebeentriggeredbyPL04andPL05.Theageprogressionmaybeaconsequenceoftheformationofthecloud.Thisscenarioisconsistentwiththenumericalsimulationsofdynamicmolecularcloudformationby Hartmannetal. ( 2012 ).Inthesesimulations,starscanformfromtheinitialdensityuctuationsresultingfromturbulenceduringtheformationofamolecularcloud.Thesestarsformbeforetheglobalgravitationalcollapseofthecloudleadstoamainphaseofstarformation. 36

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2.4.4StarformationasafunctionofdistancefromNGC2244WendthatthespatialdistributionofyoungClassI/0sourcesthroughoutthecloudhaslittleornocorrelationtolocationinthecloudordistanceformNGC2244.TheageofNGC2244isestimatedtobe2MyrswhichisconsistentwiththeagesoftheotherclustersinferredfromtheYSOratios.Ageprogressionsappeartobelimitedtosmallregions,wheresurfacedensityen-hancementsleadtomorerecentstarformationepisodes.ClustersPL02aandPL02b,spatiallycoincidentwiththevisibleedgeoftheHIIregion,haveClassIItoClassIIIratiosconsistentwitharecent(1Myr)episodeofstarformation.TheformationoftheseclustersmayhavebeentriggeredbyNGC2244,consistentwiththeX-rayanalysisof Wangetal. ( 2009 ).OuranalysisndsalocalageprogressionsurroundingREFL08whichisconsistentwiththestudiesof Romn-Zigaetal. ( 2008 ).Thisprogressiondoesnotextendthroughthecloud.ItappearsthatanyeecttheHIIregionhasonthestarformationhistoryissecondarytothatoftheprimordialcollapseofthecloud.Ouranalysissuggeststhatstarformationstartedthroughoutthecomplexduetoaprimordialcollapseandhasprogressedthroughaseriesoflocalizedepisodesofformationcloselyfollowingeachother. Table2-1 .Diskfractionandage. Age(Myr)D.F.RII:III 175%3.02-350%1.0520%0.3 Columns1and2areclusteragesandaveragediskfractionsfromtheliterature( Williams&Cieza 2011 ).Column3istheassociatedClassIItoClassIIIratio. 2.5ConclusionInouranalysisofthedierentYSOclassesintheRMCwendthattheyoftenhavedierentdensitydistributions.WeusetheYSOratiostostudyagegradientsacrossthecloudtobetterunderstandhowstarformationhasprogressed.Therelationships 37

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betweentheYSOratiosandextinctionsuggestthatstarformationinthecloudoccurspreferentiallyinhighextinctionregionsandthatthecolumndensityofgasrapidlydecreasesastheregionevolves.Thissuggestsrapidremovalofgasmayaccountforthelowstarformationecienciesobservedinmolecularclouds.Wendthatprogressionsofstarformationappeartobelocalizedwithasmalloverallagespreadacrossthecloud,consistentwithstarformationstartingacrossthecloudatroughlythesametime.ThedistributionofYSOsintheRMCshowlittleornoeectofNGC2244ontherelativeagesoftheclustersexceptforthepossibletriggeringofclustersPL02aandPL02b. Table2-2 .ClusterProperties. ClusterR.A.Dec.I/0IIIIIIIIIIRII:IIIAVH14H14 PL0197.964.32511111081.40.78.11.4PL0298.314.592106724.04.06.42.2PL02b98.314.5331551033.72.97.71.0PL03a98.384.00648260.50.410.52.5PL03b98.424.0621951243.32.29.91.9PL04a98.534.427251418101.90.810.72.4PL04b98.554.472323021171.30.47.20.8REFL0898.564.321830419117.82.4PL0598.634.322321522112.10.811.32.2PL0698.664.2141013991.10.510.81.6PL06b98.594.2001210771.10.710.21.2REFL0998.783.7153641635.74.416.62.7PL0798.883.981232ND10.61.4 Thenumberofsourcesarecountedwithin1pc(2.140)oftheclustercenters Table2-3 .AssociatedCOclumps. ClusterClump PL04115.62.1PL051912.21.7REFL08610.81.9 COclumpdatafrom Williamsetal. ( 1995 ) 38

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CHAPTER3SPITZERIRACDETECTIONANDANALYSISOFSHOCKEDMOLECULARHYDROGENEMISSION 3.1BackgroundProtostellaroutowshavestrongmolecularhydrogenemissioninthewavelengthrangecoveredbytheSpitzerInfraRedArrayCamera(IRAC).SpitzerstudiesofknownoutowsrevealthatshockedH2emissionappearsparticularlystronginthe4.5mIRACband( Noriega-Crespoetal. 2004 ; Teixeiraetal. 2008 ).ManygroupsarebeginningtovisuallyinspectIRACdatatosearchforoutowsandobjectswithextendedH2emissionbasedonthestrongemissioninthe4.5mband. Smith&Rosen ( 2005 )createdsyntheticSpitzerimagesfromtheirmodelsofprecessingprotostellarjets.Thesemodelscalculatedthepopulationoftherstthreevibrationallevelsbysolvingforstatisticalequilibriumandassuminglocalthermalequilibrium(LTE)fortherotationallevels.Theirsimulationsshowedthattheemissioninthe4.5mbandtobethestrongest,whichwasconsistentwithobservations.Intakingacensusoftheyoungstellarobjects(YSOs)inNGC1333, Gutermuthetal. ( 2008 )empiricallydeterminedanIRACcolorcutbasedonobservationsofknownshockedemissionwithinNGC1333.ThiswasusedtoremoveanypossibleshockedemissionintheirsourcelistofYSOs.DuetothemultitudeoflinesintheIRACbandsitwasthoughtthatinformationonthephysicalparametersofthegascouldnotbeascertainedfromtheSpitzerIRACdata.InanalyzingtheIRACimagesofIC443, Neufeld&Yuan ( 2008 )calculatedtheIRACbandratiosforshockedH2usingthe13strongestlinescoveredbyIRACbutonlyincludedcollisionalexcitationbyH2andHeintheircalculations.Theyfoundthemeasureduxinthe3.6mbandtobestrongerthanpredictedintheircalculations,whichmayhavebeenduetoneglectingcollisional WorkinthischapterappearsinYbarra&Lada,2010,TheAstrophysicalJournalLet-ters,Volume695,Issue1,pp.L120-L123.ReprintedwithpermissionfromtheAmericanAstronomicalSociety.2009AmericanAstronomicalSociety 39

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excitationwithatomichydrogen.Untilnow,thecolorspaceofshockedH2emissionduecollisionalexcitationwithatomichydrogen,He,andH2hasnotbeencalculated.InordertouseSpitzerIRACdatatondoutowsandstudytheirpropertieswehavecalculatedtheIRACcolorspaceofshockedH2emission. 3.2CalculationsWehavecalculatedtheintensitiesofshockedmolecularhydrogenanddeterminedthelocationoftheshockedemissionwithinIRACcolorspace.Attypicalshocktemperaturesanddensities,theexcitationofmolecularhydrogenisthroughcollisionswithHatomsandHeatoms,andwithgroundstateortho-andpara-H2molecules.Thetypicaldensi-tiesinoutowsarelessthancriticalsowedonotassumeLTE.Insteadthepopulationsoftherst47ro-vibrationalexcitedstateswerecalculatedfromsolvingtheequationsofstatisticalequilibriumwherewesetn(He)=nH=0:10,nH=n(H)+2n(H2),andn(H)=n(H2)=0:10.Theatomichydrogenfractionwassettothemedianvalueconsis-tentwithshockmodelsandthetemperaturerangewechose( LeBourlotetal. 2002 ; Timmermann 1998 ).Tosolvetheequationsweemployedanon-LTEcodebasedonthemethodby Lietal. ( 1993 ).WeusedthelatestHH2non-reactivecollisionalratecoe-cientscalculatedby Wrathmalletal. ( 2007 ).Thereactivecollisionalratecoecientswerederivedfromtherelationsof LeBourlotetal. ( 1999 ).TheratecoecientsforHeH2andH2H2collisionsarefrom LeBourlotetal. ( 1999 ).ThedegeneracyofthestatesisgivenbygJ=(2J+1)forevenJ,andgJ=3(2J+1)foroddJ.Thequadrupoletransitionprobabilitiesusedarefrom Wolniewiczetal. ( 1998 ).Wecalculatedthepopulationsofthestatesoverawiderangeofatomichydrogendensities,n(H)=50)]TJ /F6 11.955 Tf 12.61 0 Td[(105cm)]TJ /F4 7.97 Tf 6.59 0 Td[(3,andgastemperatures,T=1000K.Therelativeintensitiesof49linesthatfallwithintheIRACbands(3.08m<<10.5m)weredeterminedandusedtocalculatetheIRACbanduxesusingthelatestpublishedIRACspectralresponse( Horaetal. 2008 )andcalibrationdata( Reachetal. 2005 ).Table 3-1 liststhefractionalcontributionofthe 40

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strongestH2linestoeachIRACbandforn(H)=104cm)]TJ /F4 7.97 Tf 6.59 0 Td[(3andtemperatures2000Kand4000K. Table3-1 .FractionalcontributionofthestrongestH2linestotheIRACbands. Transition(m)IRACT=2000KT=4000K =1O(5)3.23410.510.20=2O(5)3.43710.050.08=1O(6)3.50010.140.06=2O(6)3.72310.010.02=0S(14)3.72410.010.10=1O(7)3.80710.210.13=0S(13)3.84510.040.34=0S(12)3.99620.010.04=0S(11)4.18020.170.29=0S(10)4.40820.130.12=1S(11)4.41620.010.07=0S(9)4.69420.570.33=1S(9)4.95220.020.05=0S(8)5.05230.110.14=0S(7)5.51030.610.51=1S(7)5.81030.020.10=0S(6)6.10730.240.13=0S(5)6.90740.770.66=1S(5)7.27940.020.11=0S(4)8.02440.190.12 FractionalcontributiontothetotalemissionfromtheH2linesinthebandsconvolvedwiththeIRACspectralresponseforn(H)=104cm)]TJ /F4 7.97 Tf 6.59 0 Td[(3. 3.3MolecularHydrogenEmissioninIRACColorSpaceFigure 3-1 showslocationofshockedH2gasinIRAC[3.6][4.5]vs.[4.5][5.8]colorspace.Wendthattheobservedemissioninthebandsisafunctionofkineticgastemperatureandatomichydrogendensity.Werestrictourplottogastemperaturesbelow4000KwhereH2emissionisexpectedtobethedominant.Shocksthatwouldproducegastemperaturesinexcessof4000Karelikelytobedissociative(J-type)decreasingtheabundanceofH2molecules.TheseshocksarealsolikelytoproducevibrationallyexcitedCOemissionandnestructure[FeII]emissioninadditiontotheH2emission.TheCOmolecule,whichhasahigherdissociationenergythanH2,isabletosurvive 41

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Figure3-1 .IRAC[3.6][4.5]vs.[4.5][5.8]color-colorplotindicatingtheregionoccupiedbyshockedH2.Constantdensity(dotted)andtemperature(solid)linesareindicated.Theregiontotheleftandabovethedashed-dottedlinewasempiricallydeterminedby Gutermuthetal. ( 2008 )tocontainoutows. athighershockvelocitiesandtemperatures.Inthesehighenergyshocks,CObecomesvibrationallyexcitedandemitsin=1(4.45m..4.9m)linesandcancontributesignicantlytothetotalemissionfromtheshockedgas.( Draine&Roberge 1984 ; Gonzlez-Alfonsoetal. 2002 ).Furthermore,themajorityof[FeII]linesintherangecoveredbyIRACfallwithinthe4.5mband.Consequently,4.5memissioninexcesstothecolorspacedenedbyH2at4000KislikelytotracegaswithT>4000Kplacingshockedemissionintotheupperleftportionofthecolor-colordiagram.Wechosenottousethe8mbandastheremaybedustandPAHcontaminationinthisband.PAHemissionisparticularlystronginthe8mbandanditisstillunclearwhatcontributionPAHsmayhaveintheemissionofshockedgasfromoutows.Dust 42

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continuumemissionalsobecomesapossibilityasdustmaysurvivetheshock.Furthermoreourcalculationsarerestrictedtoasingletemperaturealongthelineofsight.Inthecaseofmultipletemperaturecomponents,thecoolergaswillsignicantlycontributetothelowerexcitationpurerotationallines,0S(4)and0S(5),thatdominatetheemissioninthe8mband.The8mbandwouldthentracethecoolertemperaturecomponentwhiletheotherbandswouldbemoresensitivetothehottergas.Thusouranalysiscanincludegascontainingmultipletemperaturecomponentsalongthelineofsightbutwillstillberestrictedtoanalyzingonlythehottergas.AsseeninFigure 3-1 ,theshockedH2liesinawelldenedlocationinthecolor-colordiagram.Forcomparison,thelocationofYSOsisalsoshowninthegurebasedonthecriteriaof Gutermuthetal. ( 2008 )and Megeathetal. ( 2004 ).ShockedH2gaswithsucientlyhightemperatureandatomichydrogendensityisfoundinauniquelocationonthisdiagramandcanbedistinguishedfromYSOs.Thisisconsistentwiththeempiricallydeterminedcolorcutof Gutermuthetal. ( 2008 ).Thereforethesecolorsoeranunambiguousmethodforsearchingforshockedgasfromoutows/jets.However,thereisoverlapinIRACcolorspacebetweenlowtemperatureshockedH2gasandprotostellarsources.ConsequentlysurveyssearchingforoutowsusingIRACcoloranalysiswillberestrictedtondingowscontaininghigherexcitationgas.Additionaldataatdierentwavelengths(2MASS,MIPS,etc.)and/ormorphologymaybeabletobreakthisdegeneracy.Ourresultsareconsistentwithempiricalobservationsofstrong4.5memissioninoutowsandwiththehydrodynamicsimulationsof Smith&Rosen ( 2005 ).Usingthiscoloranalysis,twomethodscanbeappliedtoidentifyoutowsintheimages:1)Visualinspectionof3-colorimagesconstructedoutofthe3.6m,4.5m,and5.8mbanddatawithappropriatescalingtoenhancetheshockedemission,and2)analysisofthephotometryoftheeldwherefeaturesconsistentwithcolorsofshockedH2emissionareselected.Thiscanbeaccomplishedbyevaluatingthecolorpixelbypixelacrosstheeld. 43

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ThelocationoftheshockedH2incolorspacedependsonitstemperature.Thereforecoloranalysisprovidesanewwaytoprobethetemperaturestructureofthegas.Thiscanbeaccomplishedbyevaluatingthecolorspixelbypixelacrosstheeld.ThecolorscanthenbecomparedtothecolorsofshockedH2andthetemperatureofthegascanbeestimated.Resultingtemperaturemapsarerestrictedtotemperaturesbetween20004000Kandhighatomichydrogendensities.ThecolorspaceforH2attemperaturelessthan2000KmovesfurtherintothecolorspaceofClassI/0objectsanditbecomesmorelikelytomisidentifyscatteredlightfromYSOsasH2emission.Notethat,atlowatomichydrogendensitiestheconstanttemperaturelinesstarttoconvergeandthustemperatureestimatesfromthisregionofcolorspacemayhavelargeuncertainties. 3.4ExampleWeappliedouranalysistoSpitzerarchivaldataoftheknownoutowHH54.WeevaluatedtheIRACcolorsateachpixelintheeldofHH54.Themedianvalueoftheimagewasusedtoestimatethebackgroundandwassubtractedfromtheimages.Figure 3-2 showsthecolor-colordiagramfortheknots(A,B,C,E,K,M)ofshockedH2previouslystudiedby Gianninietal. ( 2006 ).Weplotallthepixelsonthediagramthatareencompassedbytheknots.ThemajorityofpointsfallwithinourcalculatedcolorspaceforshockedH2emission.OneexceptionisknotAwhichcontainsseveralpixelswithcolorsthatfallmorethan3outsidethe4000Kboundary.Thisregionofcolorspacewithexcess4.5memissionisconsistentwithhighergastemperaturesandpossibleadditionalemissionfromCO=1and[FeII]. Gianninietal. ( 2006 )obtainedspectroscopicdataofvariousknotsinHH54inthenear-infraredandusedH2emissionlinestoestimatetherotationalandvibrationalexcitationaltemperaturesofthegas.WecreatedatemperaturemapofHH54(Figure 3-3 )byselectingthepixelswhosecolorsfallwithintherangeweidentiedasbelongingtoshockedH2(T=2000K)and[4.5][5.8]1.5,andthenestimatedthetemperatureofthegasbasedonthepixelslocationincolorspace.Theestimatedtemperaturesare 44

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comparedtothevibrational(1)excitationtemperaturesobtainedby Gianninietal. ( 2006 )inTable 3-2 .Becausetypicalatomichydrogendensitiesinshocksarelessthancritical,thegascannotbeassumedtobeinLTE.Intheseenvironmentstherotationaltemperaturesareoftenfarbelowthekineticgastemperature,whilethero-vibrational1excitationtemperaturesareclosetothekineticgastemperature.Formostoftheknotsthetemperaturesweestimatefromcoloranalysisandthespectroscopicallydeterminedtemperaturesareconsistent.Thereisanadditionalknot,labeledI(J2000=12:55:54.8,J2000=-76:56:06),5arcsec-ondstotheeastofknotCseenintheIRACimagesthatisnotfoundintheNIRimagesofHH54whichweidentifyasthemid-infraredcounterparttotheopticalknotHH54I( Sandelletal. 1987 ).Thetemperatureofthegasinthisknotpeaksat3500KasseeninFigure 3-2 and 3-3 .Thisknotisalsofoundontheedgeofthe[NeII]12.8mmapofHH54by Neufeldetal. ( 2006 ).Thepresenceofthene-structure[NeII]lineisconsistentwiththehightemperaturestructureofthisknot.KnotB(T2600K)isalsofoundtobespatiallycoincidentwithstrong[NeII]12.8memission.Thedistributionofthe[FeII]26mline( Neufeldetal. 2006 )coversaregioncontainingknotsA,B,M.Wendthatspatialdistributionofne-structureemissionlinesisconsistentwithregionswithinourtemperaturemapwhereT&2600K.KnotsA,B,andIarespatiallyalignedwitheachotherasindicatedbythegreenlineinFigure3.Thesehightemperatureknotsmaytracethejetcomponentoftheoutow.ThislinepointsinthedirectionofIRAS12496-7650whichisbelievedtobethesourceoftheoutow. 3.5SummaryWehavequantitativelyshownthatanalysisofSpitzerdatacanbeusedtodiscoverandcharacterizeemissionfromprotostellaroutows.ShockedH2withsucientlyhightemperatureandneutralatomichydrogendensitycanbedistinguishedunambiguouslyfromstellarobjectsinIRACcolorspace.IRACcoloranalysisisusefulforstudyingintermediate-excitationshockedgaswithinthetemperaturerangeT=2000K. 45

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Figure3-2 .IRACcolor-colorplotforidentiedknotsinHH54.Eachpointrepresentsthecolorsatanindividualpixelwithintheknots.Dierentknotsarerepresentedwithdierentsymbols. Table3-2 .TemperatureestimatesofHH54. Knot(J2000)(J2000)TgasT1 A12:55:49.5-76:56:303300500K3000150KB12:55:51.1-76:56:212600300K3000140KC12:55:53.1-76:56:062200100K2960150KE12:55:53.8-76:56:232000100K250090KK12:55:54.3-76:56:252100100K250090KM12:55:51.6-76:56:132800400K3000140K Highertemperaturegasmaycontainsignicantcontributionfromioniclineslike[FeII]andalsofromtheCO=1emissionband.Evenwiththislimitation,SpitzerIRACdataprovidesausefultoolinthestudyofoutows.Inparticular,IRACcoloranalysiscanbeusedtoprobethethermalstructureofthegaswithouttheneedofusingspectroscopicdata. 46

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Figure3-3 .IRAC4.5mimageandtemperaturemapofHH54.A)IRAC4.5mimage.Imagecenterisat(J2000)=12h55m49:s5(J2000)=-765602200.Individualknotsareidentiedandlabeledaccordingto Gianninietal. ( 2006 ).KnotI,notseenontheNIR,isidentiedastheopticalcounterparttoHH54I.B)TemperaturemapofHH54basedonIRACcolor-coloranalysisfor2000KT4000K.Theblackcontourlevelsare2000K,2500K,3000K,and3500K.ThegreenlineconnectingthehighertemperatureknotsA,B,andIpointstowardtheproposedsourceIRAS12496-7650. 47

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CHAPTER4SPITZERANDNEAR-INFRAREDOBSERVATIONSOFANEWBI-PLOARPROTOSTELLAROUTFLOWINTHEROSETTEMOLECULARCLOUD 4.1BackgroundOutowsandjetsfromyoungstellarobjects(YSOs)accompanytheearlystagesofstarformation.Outowscanmanifestthemselvesasjetsandknotsofshockedmaterialvisibleatopticalandnear-infraredwavelengthsandalsomolecularemissionobservableatlongerwavelengths.TheoutowingmaterialplaysaroleinremovingtheexcessangularmomentumfromtheYSOsallowingthemtoevolveintostars.Outowsareabletotracethehistoryofmasslossandaccretionoftheirdrivingsources.Studyingthestructureandpropertiesoftheseowsmayprovidecluestounderstandingtheconnectionbetweenjetsandtheassociatedwideanglemolecularows( Reipurth&Bally 2001 ).Additionally,thisoutowingmaterialinteractswithitssurroundingsandmayaectitsenvironment,possiblyregulatingfurtherstarformationandclusterevolution.Theenergyandmomentuminputtedbyoutowsmaydisruptthesurroundingambientgas,contributetotheturbulenceinthecloud,andaectchemicalprocesses( Bally 2007 ). Ybarra&Lada ( 2009 )developedatechniquetostudythethermalstructureofshockedH2gasusingcoloranalysisofobservationsfromtheSpitzerInfraRedArrayCamera(IRAC).GiventhevastamountofSpitzerdataavailable,thistechniquecanbeusedtosurveylargeregionsandsimultaneouslyndandanalyzeshockedemission.TheIRACcoloranalysisenablestheconstructionoftemperaturemapsoftheshockedgaswhichmayinturnbeusedtoprobetheinteractionofoutowwithitssurroundings.Thesemapsmayalsobeusedtocomparethepropertiesofoutowwiththoseofsimulationsallowingabetterunderstandingofthe WorkinthischapterappearsinYbarraetal.,2010,TheAstrophysicalJournal,Vol-ume714,Issue1,pp.469-475.ReprintedwithpermissionfromtheAmericanAstronomi-calSociety.2010AmericanAstronomicalSociety 48

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Figure4-1 .SpitzerIRACimagesoftheoutow.Theoriginissetat(,)(J2000)=(06h35m25:s0,+035602100). physicsinvolvedandestimatingtheenergyandmomentuminputtedbyoutowsintotheirenvironment.TheRosetteMolecularCloud(RMC)isastarformingregionlocatedatadistanceof1.6kpc.Near-infraredimagingstudieshaverevealednineembeddedclustersacrossthecloud( Phelps&Lada 1997 ; Romn-Zigaetal. 2008 ).Outowactivityinthecloudhasbeenrevealedthroughthe[SII]narrowbandimagingsurveyof Ybarra&Phelps ( 2004 )andthe12COsurveyof Dentetal. ( 2009 ).InananalysisoftheSpitzerIRACimagesoftheRosetteMolecularCloud,wehavediscoveredastructurewiththemorphologyofabipolaroutowthatisvisibleintheimagesfromallfourIRACbands(Figure 4-1 ).Thisstructurecanbeseenintheimagespublishedby Poultonetal. ( 2008 )althoughitisnotdiscussedintheirpaper.Inthisstudyweanalyzetheoutowusingnear-infrared(NIR)narrow-bandimagingoftheowtoconrmthepresenceofshockedgasinferredfromanalysisofthetheIRACimages.WeimprovetheIRACcoloranalysisof Ybarra&Lada ( 2009 )anduseittocreatetemperatureandcolumndensitymapsoftheoutow.UsingboththeNIRandIRACdata,weprobethephysicalconditionsandstructureoftheoutow. 4.2ObservationsandDataReduction 4.2.1SpitzerIRACandMIPSdatareductionWeusedMIPS24mandIRAC3.6.0mdatafromprogram3391(PI:Bonnel)availableintheSpitzerarchive.TheIRACframeswereprocessedusingtheSpitzerScience 49

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Center(SSC)IRACPipelinev14.0,andmosaicswerecreatedfromthebasiccalibrateddata(BCD)framesusingacustomIDLprogram(see Gutermuthetal. ( 2008 )fordetails).TheMIPSframeswereprocessedusingtheMIPSDataAnalysisTool( Gordonetal. 2005 ). 4.2.2Near-infraredmolecularhydrogenobservationsanddatareductionNear-infrared,narrow-bandobservationsoftheoutowwereobtainedwiththeInfraredSidePort-Imager(ISPI)ontheBlanco4metertelescopeattheCerroTololoInter-AmericanObservatory(CTIO).ISPIemploysa20482048HgCdTeHawaii-2arraywitha10.2510.25arcmineldofviewandaplatescaleof0.30500pixel)]TJ /F4 7.97 Tf 6.59 0 Td[(1.Theout-owwasimagedusingtheH21S(2)2.034mlter(c=2.0336m,==.007),H21S(1)2.122mlter(c=2.1262m,==.01),andKcontltercenteredat2.1462m.Thetelescopewasditheredwitha20pointditherpatternwithaintegrationtimeof60sateachditherposition.Theimagesweretakenonthenightsof2008December17and2008December19withtotalintegrationtimeof40minutesineachlter.Therawimageswereatelded,correctedforbadpixels,andlinearizedusingthetaskosirisfromtheCTIOInfraredReductionpackage.Foreachimage,askyframewascreatedbymediancombiningtheditheredimagesclosestintimetotheimage.TheIRAFtasksmsctpeakandmscimage,whicharepartoftheIRAFMosaicDataReductionPackage,mscred,wereusedtocorrecttheimagesforgeometricdistortions.Thehighorderpolynomialdistortiontermswerecalculatedwithmsctpeakusingthe2MASSPointSourceCatalogasthereferencecatalogandthedistortioncorrectionwasappliedwithmscimage.Thecorrectedimageswerealignedandthencombinedtoformthenalscienceimages. 4.3ResultsandAnalysisFigure 4-1 showstheoutowinallfourIRACbands.TheoutowappearsaspatchyregionsofdiuseemissionwithanoverallstructurethatiselongatedandcollimatedintheE-Wdirection.Figure 4-2 showsthenarrowbandnear-infraredemissionimagesofthe 50

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outow.TheNIRH2knotscoincidewiththediuseemissionseenintheIRACimages.TheNIRH2imagesconrmthepresenceofshockedgasandtheinterpretationthatthisstructureisanoutow.Theeasternendappearstotruncateatabowshock.Slightlywestofthebowshock,theH2imagesrevealasmallscalechaoticstructurefollowedbyamorelinearchainofknots.Thewesternendoftheoutowappearsslightlydeectednorthwardfollowedbyabrightknot(g)andthenacomplexstructureofsmallerknots.TheNIRimageswereuxcalibratedtothe2MASSKsbandbydeterminingthemagnitudedierencebetweenthe2MASSKsbandcatalogvaluesandtheISPIimagemagnitudesforstarsincommon.ThezeropointuxineachNIRimageaftercalibrationisthenthelterbandwidthmultipliedbythe2MASSKs-bandzeropointuxdensity.Thisresultsinarelationbetweenthecountssec)]TJ /F4 7.97 Tf 6.59 -.01 Td[(1ineachlterimageandtheuxinWcm)]TJ /F4 7.97 Tf 6.58 0 Td[(2.ThenarrowbandcontinuumKcontimageswerescaledandsubsequentlysubtractedfromtheH2lineimages.Figures 4-2 cand 4-2 dshowthecontinuumsubtractedH21S(1)2.122mandH21S(2)2.034mlineimages.ThequalityofthesubtractionisgoodalthoughtherearesomesubtractionresidualsfromthebrighteststarspresentinthesubtractedimagesduetodierencesinwavelengthandPSFcombinedwithchangingatmosphericconditions.Basedontheobservation,thisoutowhasbeengiventhedesignationMHO1321intheCatalogueofMolecularHydrogenEmission-LineObjects(MHOs)inOutowsfromYoungStars1( Davisetal. 2010 ).TheuxesoftheindividualH2knotscomprisingthisoutowweredeterminedusingacircularapertureonthecontinuumsubtractedimages.Table 4-1 liststheNIRuxesoftheH2emissionknots.Theuxuncertaintyiscomposedofthermsbackground,poissonnoise,anduncertaintyfromtheuxcalibration. 1MHOcatalogueishostedbyLiverpoolJohnMooresUniversity. http://www.astro.ljmu.ac.uk/MHCat/ 51

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Figure4-2 .Near-infraredimagesoftheoutow.A)H21S(1)2.122mline.B)Kcont2.146mline.C)ContinuumsubtractedH21S(1)2.122m.D)ContinuumsubtractedH21S(2)2.034m.Thehorizontalscaleisinarcminutesandtheverticalscaleisinarcseconds.Theoriginissetat(,)(J2000)=(06h35m25:s0,+035602100). 4.3.1IRACcolorspaceofshockedgasInordertostudythestructureoftheshockedgas,weappliedtheIRACcoloranalysismethoddevelopedby Ybarra&Lada ( 2009 ).WeimprovedthecoloranalysismethodbyincludingtheeectsofCO=1bandemissioninthetotalemissionoftheshockedgas.ThedistributionofthepopulationofpurerotationallevelsofCOduetocollisionalexcitationwithH2,H,andHewascalculatedusingtheratecoecientsof Draine&Roberge ( 1984 ).Weemployedthemethodof Gonzlez-Alfonsoetal. ( 2002 )tocalculatetherelativerotationalpopulationfortheCO=1vibrationallevel.TheEinsteinAvaluesfortheCO=1rovibrationaltransitionswereobtainedusingtheoscillator 52

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strengthsof Hure&Roue ( 1993 ).Inourcalculations,wesetnH=n(H)+2n(H2),n(He)=nH=0:1andn(CO)=nH=710)]TJ /F4 7.97 Tf 6.59 0 Td[(5.ThefractionofatomictomolecularhydrogenwasestimatedbyconsideringtherateofcollisionaldissociationbyHatoms,Rd=1:010)]TJ /F4 7.97 Tf 6.59 0 Td[(10exp()]TJ /F6 11.955 Tf 9.3 0 Td[(52000=T)cm3s)]TJ /F4 7.97 Tf 6.59 0 Td[(1( LeBourlotetal. 2002 )andtherateofformationongrains,Rf=3:810)]TJ /F4 7.97 Tf 6.59 0 Td[(17T)]TJ /F4 7.97 Tf 6.59 0 Td[(1:5cm3s)]TJ /F4 7.97 Tf 6.59 0 Td[(1,derivedfrom Hollenbach&McKee ( 1979 )withthecoolingratesforH2andH2O( LeBourlotetal. 1999 2002 ).Figure 4-3 showsthelocationofshockedgasinIRAC[3.6][4.5]versus[4.5][5.8]colorspaceformaximumshocktemperatureofTmax=6103KforgastemperaturesT=1500KanddensitiesnH=1057cm)]TJ /F4 7.97 Tf 6.59 0 Td[(3.ThesquarebracketsrefertoIRACmagnitudes.Thepost-shockfractionofatomichydrogenwasfoundtoben(H)=nH110)]TJ /F4 7.97 Tf 6.58 -.01 Td[(3whichisconsistentwithsimulationsofnon-dissociativeC-shocks( Wilgenbusetal. 2000 ).Inthesimulationsby Wilgenbusetal. ( 2000 )itwasfoundthattheatomicfractionisrelativelyconstantoverawiderangeofmaximumtemperatures.Thereforewewillassumeourcolorspacetoberepresentativeofnon-dissociativeC-shocksingeneral.ThelocationoftheshockedemissioninIRACcolorspacedependsonthegasdensity,fractionofatomichydrogen,andthekinetictemperatureofthegas.The[4.5][5.8]colorisstronglydependentontemperature,whilethe[3.6][4.5]colorhasastrongdependenceontheatomichydrogendensity.Athighdensities,thedependenceondensitydecreasesastheH2gasmovestowardlocalthermalequilibrium(LTE).Theslopeofthereddeningvectorissimilartotheapproximateslopeoftheconstanttemperaturelines.Thustemperaturemapsofhighextinctionregionsremainaccurateeveniftheextinctioncannotbeaccountedfor.However,unlessextinctioncanbecorrectedfor,accuratedensityinformationmaynotbeattainable. 53

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Wetananalyticformtotherelationshipbetweencolorandtemperatureforthenon-dissociativecase, T3=4:19)]TJ /F6 11.955 Tf 11.95 0 Td[(0:97([3:6])]TJ /F6 11.955 Tf 7.97 0 Td[([4:5]))]TJ /F6 11.955 Tf 11.95 0 Td[(2:11([4:5])]TJ /F6 11.955 Tf 7.97 0 Td[([5:8])+0:59([3:6])]TJ /F6 11.955 Tf 7.97 0 Td[([4:5])2+0:50([4:5])]TJ /F6 11.955 Tf 7.97 0 Td[([5:8])2whereT3=T=103inthecolorspacedenedby2.0>[3.6][4.5]>)]TJ /F1 11.955 Tf 9.3 0 Td[(0.21([4.5][5.8])+1.5,and)]TJ /F1 11.955 Tf 9.3 0 Td[(0.2<[4.5][5.8]<2.0.Thedierencebetweentheanalytictandthecalculatedtemperature-colorrelationoverthedenedrangeislessthan10%.Additionally,onecanusetheuxinthe3.6mimagetoestimatethecolumndensityoftheshockedH2.Usingourcalculationswetthefollowinganalyticformtotherelationshipbetweencolumndensity,IRAC3.6muxdensity,andtemperature, log(NH2=F3:6)=23:11)]TJ /F6 11.955 Tf 11.95 0 Td[(3:40T3+0:742T23)]TJ /F6 11.955 Tf 9.3 0 Td[(0:0589T33)]TJ /F6 11.955 Tf 11.96 0 Td[(0:071n6+0:012n6T3whereNH2isthecolumndensityofshockedH2incm)]TJ /F4 7.97 Tf 6.59 0 Td[(2,F3:6istheIRAC3.6mbanduxdensityinunitsofMJysr)]TJ /F4 7.97 Tf 6.59 0 Td[(1,andn6=nH=106for1.5
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Figure4-3 .IRACcolor-colorplotindicatingtheregionoccupiedbyshockedgascomposedofH2andCOforTmax=6103K. thedistributionincolorspaceforthedissociativeshocktoprimarilylieat[4.5][5.8]<0.Thuswedenethedomainofthedissociativeshockedgasincolorspacetobe[4.5][5.8]<0and[3.6][4.5]>1.5,whereaswedenethecolordomainofnon-dissociategastolieprimarilyat[4.5][5.8]>0.Byanalyzingthecolordistributionofanoutow,itmaybepossibletodistinguishbetweenthecases.Apixeldensitydistribution,producedfrombinningthecolorsofeachpixelinthetheoutow,canrevealthenatureoftheoutowbyshowingwheremostofthepixelslieincolorspace.ItshouldbenotedthattheIRACcoloranalysisassumesdustandPAHemissionisnegligible.Inordertopreventdustemissionfromaectingthecoloranalysis,the8mIRACcolorisnotusedasthereisevidenceinsomeshocksofcontinuumdustemissionwithinthatwavelengthrangecoveredbythe8mchannel(eg. Smithetal. 2006 ). 55

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Figure4-4 .IRACcolor-colorplotindicatingtheregionoccupiedbydissociativelyshockedgascomposedofH2andCO. Additionally,PAHsareverylikelydestroyedinshocks.Inarecentstudy, Micelottaetal. ( 2010 )showthatstrongshockscandestroyPAHsorseverelydenaturethem. 4.3.2IRACcoloranalysisofMHO1321TheIRAC8mimageoftheoutowregionrevealspatchesofabsorptionagainstthediusebackground(Figure1).Ofparticularinterestisadarkpatchseeninabsorptionthatbisectstheoutow.Wecreatedanextinctionmapfromthe8mdatausingasmallscalemedianlterassumingauniformbackground.Weappliedthisextinctionmaptotheimagesoftheoutowregionusingthemid-infraredreddeninglaw(KP,v5.0)of Chapmanetal. ( 2009 ).However,thisisnotabletoaccountforthetotalextinctioninthelineofsighttowardtheoutow.Nonetheless,thetemperature-colorrelationisinsensitivetoextinctionfornon-dissociativeshocks.WeestimatethebackgroundusingaringmedianlterandsubsequentlyremovethisbackgroundfromtheIRAC3.6m,4.5m,and5.8 56

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mimages.Aringmedianlterisamedianlterfromwhichonlythepixelswithinanannulusareusedincalculatingthemedian( Secker 1995 ).Thescaleofthislterneedstobelargerthanthescaleoftheshockedemissionotherwisethebackgroundwillbeoverestimated,yetsmallenoughtoaccountforthelargescalebackgrounductuations.TheimageswereshiftedandregisteredwitheachotherandthenIRACcolorsateachpixellocationweredetermined.Figure 4-5 showsthepixeldensityinIRACcolorspacefortheknotsoftheoutow.DuetothelackofpixelswhosecolorsareinorneartheCOdominatedregionandourcriteriaabovefornon-dissociativeshocks,weconcludethatthisshockismostlynon-dissociativeandwecanthereforeestimatethethermalstructurebasedoncoloranalysis.Wecomparedthecolorstothoseofnon-dissociativeshockedgaswiththecuto[4.5][5.8]1.5.Athermalmapwascreatedbyestimatingthegastemperaturebasedonthelocationofthepixelsincolorspace.Figure6showsthethermalmapoftheoutow.WendthatmostoftheNIRH2knotsarespatiallycoincidentwiththehightem-peratureregionsoftheow.However,knotsaandvdonothaveacorrespondingIRACderivedtemperature.TheNIRimagesrevealstarsinthelineofsightfortheseknotswhichaddtotheemissionandpreventsIRACcoloranalysisfromderivingtemperatures.Sevenoftheknotshaveestimatedtemperaturesgreaterorequalto3103K.Bycom-biningtheNIRinfraredandtemperaturedataitispossibletoestimatetheextinctiontowardsthebrightestknots.Forthisweusedtheextinctioncross-sectionsof Weingartner&Draine ( 2001 ).ThemedianextinctiontotheknotsisAV=27.Theknotsjandkinthevicinityofthedarkclumphavehigherextinctioncomparedtotherestoftheknots.Weusethemedianextinctionvaluetode-reddenthe3.6muxanduseitcreateacolumndensitymapwithourcolumndensitytemperaturerelation.Figure 4-7 showthecolumndensitymapofshockedH2intheow.WendthatthereisalsoacorrespondencebetweentheNIRH2knotsandregionsofhighercolumndensity.Usingtheestablished 57

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Figure4-5 .TheoutowinIRACcolorspace.Contoursindicatethepixeldensityoftheoutowknots.ThedistributionofpixelsandthelackofpixelsintheCOdominatedre-gionindicatenon-dissociativeshocks. Figure4-6 .ThermalmapoftheoutowbasedoncoloranalysisoftheIRACdata.ThecontourlevelsindicateT=1500K,2500K,3000K,4000K.Theoriginissetat(,)(J2000)=(06h35m25:s0,+035602100). distancetotheRMCof1.6kpcandthecolumndensitymapwecalculatethetotalmassoftheshockedH2(T>2000K)intheoutowtobe3.51030g(210)]TJ /F4 7.97 Tf 6.59 0 Td[(3M). 58

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Figure4-7 .ColumndensitymapforH2oftheoutowbasedoncoloranalysisoftheIRACdata.ThecontourlevelsindicateNH2=21017cm)]TJ /F4 7.97 Tf 6.59 0 Td[(2,51017cm)]TJ /F4 7.97 Tf 6.59 0 Td[(2,11018cm)]TJ /F4 7.97 Tf 6.59 0 Td[(2,21018cm)]TJ /F4 7.97 Tf 6.58 0 Td[(2.Theoriginissetat(,)(J2000)=(06h35m25:s0,+035602100). 4.3.3OutowsourceThesourceoftheoutowisnotseenintheNIRnorintheIRACimages.How-ever,inspectionoftheMIPS24mimagerevealsasource((,)(J2000)=(06h35m25:s0,+035602100))bisectingtheoutow(Figure 4-8 ).Moreover,thissourceisspatiallyco-incidentwithadarkpatchseeninthe8mimage.Thispatchiselongatednearlyperpendiculartotheoutowandthenorthwestpartofithasthemorphologyofanout-owcavity.Thedarkpatchisseeninthecontoursthatindicatemasssurfacedensitiesobtainedthroughextinctionmappingofthe8mimagingdatabythemethodof Butler&Tan ( 2009 ).Thecontourlevelscorrespondtomasssurfacedensitiesof=(2.5,4.0,5.0,6.0)10)]TJ /F4 7.97 Tf 6.59 0 Td[(3gcm)]TJ /F4 7.97 Tf 6.59 0 Td[(2.Thissmallcloudmaybearemnantofthecorefromwhichtheprotostarformed.Themorphologyofthenorthernendofthecloudappearsasabi-polaroutowcavitywithanopeningangle30.H21S(1)surfacebrightnesscontoursareoverlaidontheMIPS24mimagethatbisecttheMIPSsourceandacoincidentwiththecavityofthedarkcloud.ThissourceisalsodetectedintheMIPS70mandMIPS160mimagingdata.However,weareunabletoestimatetheuxintheMIPS70mbandimageduetoincompletecoverageandpossiblecontaminationfromtheadjacentknot(j)whichmayhaveemissionfromdustandthe63m[OI]line( Reipurth&Bally 2001 ).Similarly,theMIPS160mbandimagemayincludeemissionfromtheknotinadditiontothesource.ThissourceisnotdetectedatshorterwavelengthsandthuscanbeclassiedasaClass0protostar.Weproposethisnewlydiscoveredprotostartobethesourceofthe 59

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outow.Additionally,usingthecolumndensitymap,wendthatthemassoftheshockedH2totheeast(1.81030g)ofthissourceisalmostequaltothemasswestofthesource(1.71030g).Faintextended24memissionisalsodetectedatthelocationsofthebrightestH2knots(g&j).Thismayarisefromne-structure[FeII]lineswithintheMIPS24mband( Velusamyetal. 2007 ).ThisisconsistentwithourIRACcoloranalysisoftheseknotsthatrevealthemtobehightemperatureregions(T3.2103K).ThisconsistencybetweentheIRACcoloranalysisandtheMIPS24memissionvalidatesourusageofthecolorspacefornon-dissociativeshocks. 4.4Discussion 4.4.1StructureoftheoutowThelongaxisoftheowextendsto3.30.Withadistanceof1.6kpctotheRMC,theowwouldhaveaprojectedtotallengthof1.5pc.Theeastlobeextends2.30fromtheMIPSsourcetothebowshock,whilethewestlobeextendsonly10.Assumingaprojectedoutowvelocityof100kms)]TJ /F4 7.97 Tf 6.59 0 Td[(1,usingtheeastlobeweestimatetheageoftheoutowtobe104years.ThisageisconsistentwiththetypicalageofaClass0sourceandthusthisoutowmayprovideanaccretionrecordoftheprotostar( Reipurth&Bally 2001 ).Wecanestimatethemassuxoftheoutowas_MM(H2)vtltwherevtistheprojectedoutowvelcocityandltistheprojectedoutowlength.Assumingthetypicalvalueofvt=100kms)]TJ /F4 7.97 Tf 6.59 0 Td[(1andusingthevaluesfortheH2massandlengthoftheeastlobe,weestimateamassuxof_M10)]TJ /F4 7.97 Tf 6.59 0 Td[(7Myr)]TJ /F4 7.97 Tf 6.59 0 Td[(1.Thisvalueisconsistentwiththoseobtainedfromotheroutowsusingspectroscopicdata( Podioetal. 2006 ).TheNIRH2datarevealsthehighertemperatureregionsoftheoutowseenintheIRACimages.TheIRACimagesalsoshowthecoolerregionsoftheowastheIRACbandscontainpurerotationalH2linesinadditionto=1and=2ro-vibrationallines. 60

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Figure4-8 .MIPS24mimageoftheoutowsource.Thegreencontoursshowthedarkcloudthatbisecttheoutowandindicatethevalues(2.5,4.0,5.0,and6.0)10)]TJ /F4 7.97 Tf 6.58 0 Td[(3gcm)]TJ /F4 7.97 Tf 6.58 0 Td[(2obtainedthroughextinctionmappingusingtheIRAC8mimagingdata( Butler&Tan 2009 ).ThebluecontoursareH21S(1)surfacebrightnesscontourswithlevelsindicating(0.5,1.0,2.0,5.0)10)]TJ /F4 7.97 Tf 6.58 0 Td[(18Wm)]TJ /F4 7.97 Tf 6.59 0 Td[(2sr)]TJ /F4 7.97 Tf 6.59 0 Td[(1.TheH2contoursrevealthelocationoftheoutow.Thescaleoftheimageaxesisinarcseconds.Theoriginissetat(,)(J2000)=(06h35m25:s0,+035602100). 61

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TheowisspatiallycoincidentwithtwolobesofhighvelocityCOgasobservedby Dentetal. ( 2009 ).SimilartomanyHHowswhichextendfurtherthantheirCOcounterpart,wendtheeasternhalftoextendbeyondthetheeasternCOlobe.TheeastendoftheH2owendsinalargebowshock,whilethewestendrevealsacomplexstructureresemblingeitherabrokenupbowshockormultiplesmallerbowshocks.Althoughtheoutowislinearonlargescales,theIRACandH2datarevealaregionintheeasternlobebeforethebowshockwithamorechaoticstructure.Thisdeviationfromalinearprogressionofknotsmaybeduetoapossibleinteractionwithanotheroutow.TheCOobservationsof Dentetal. ( 2009 )revealanotherowintheNE-SWdirectionoriginatingfromtheembeddedclusterPL07( Phelps&Lada 1997 )thatpointstowardthisregion.Acollisionbetweenthetwoowsmayexplainthemorphologyandhightemperatureofknotr.Thedistributionofknotsmayalsobeduetovariationsininjetdirectionovertimeandthusanindicationofjetprecession. 4.4.2DeectionoftheoutowThewesternendoftheoutowappearsslightlybentnorthward.Theoutowisdeectedbyanangled=20whereitappearstograzethedensestregionwithinthedarkpatch.Thedeectionangleremainssmallandappearstodecreaseslightlybeyondtheinteractionregion.Thisisconsistentwiththesimulationsby Baeketal. ( 2009 )ofoutowscollidingwithdensecloudcoreswheretheimpactparameterislarge.Thedeectionoftheoutowmayexplainwhythewesternendoftheowisshorterthantheeasternendastheoutowvelocityisexpectedtodecreaseafterthecollision( Raga&Canto 1995 ).ThisisconsistentwiththeIRACcoloranalysisthatrevealshightemperatureshockedgas(knotj)totheeastofthecollision.Iftheoutowiscomposedofepisodicejectionofmaterial,theremaybecollisionbetweenclumpsofmaterialmovingthroughtheowduetothevelocitychange( Raga&Cant 2003 ).Asthesesuccessiveclumpscollidetheymaygiverisetothehightem-peratureandhighcolumndensityregion(g)foundslightlywestofthedeection.This 62

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interactionmayalsoexplainwhythewesternlobelacksthebowshockstructureseenintheeasternend. 4.5ConclusionsWepresentthediscoveryofanewbi-polaroutowintheRosetteMolecularCloudanduseNIRnarrowbandandSpitzerimagingdatatostudytheow.WeshowthatIRACcoloranalysiscanbeusedtointerprettheinteractionofanoutowwithitssurroundingenvironment.UsingourcalculationsoftheIRACspaceofnon-dissociativeshockedgaswetanalyticformstothecolor-temperatureandcolumndensity-temperaturerelationships.WeverifythatIRACcoloranalysiscanrevealregionsofshockedgasandndthattheNIRH2knotscorrespondtoregionsofhightemperatureandorcolumndensitydeterminedthroughcoloranalysis.WenddiuseMIPS24memission,mostlikelyfrom[FeII]lines,tobecoincidentwithregionsofhightemperaturethusconrmingthevalidityofusingthenon-dissociativeshockIRACcolorspaceTheNIRlineratioscombinedwiththetemperatureestimatesallowforthedeterminationofextinctionalongthelineofsightwhichisusedtocreateacolumndensitymapoftheshockedH2gas.Wededucethattheasymmetryintheoutowisduetointeractionswiththedensematerialtothewestoftheoutowsourcecausingdeectionandpossiblydecelerationoftheoutowingmaterial. Table4-1 .PositionsanduxestimatesfortheNIRH2knotsofMHO1321. KnotR.A.(J2000)Dec.(J2000)H21S(2)H21S(1) a06:35:20.08+03:56:37.94.12.07.62.2b06:35:21.64+03:56:28.82.21.48.92.2c06:35:21.82+03:56:32.33.91.912.52.4d06:35:21.85+03:56:27.64.21.815.62.8e06:35:22.19+03:56:29.52.21.710.12.4f06:35:22.70+03:56:33.22.01.64.92.1g06:35:22.90+03:56:28.715.53.852.45.8h06:35:23.21+03:56:17.31.21.53.31.8i06:35:23.77+03:56:24.11.81.65.21.9 63

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Table 4-1 .Continued. KnotR.A.(J2000)Dec.(J2000)H21S(2)H21S(1) j06:35:24.33+03:56:21.64.72.220.83.4k06:35:24.61+03:56:20.72.51.610.42.4l06:35:25.26+03:56:21.42.41.68.32.1m06:35:25.46+03:56:21.61.51.34.31.8n06:35:26.13+03:56:20.92.01.78.62.5o06:35:26.57+03:56:23.51.41.43.31.6p06:35:27.90+03:56:18.33.11.911.82.6q06:35:28.56+03:56:25.73.02.010.82.6r06:35:29.02+03:56:14.212.83.442.35.0s06:35:29.18+03:56:18.62.11.66.92.0t06:35:31.16+03:56:15.81.61.54.31.8u06:35:33.64+03:56:16.63.01.711.32.6v06:35:33.85+03:56:18.92.81.97.92.1w06:35:34.04+03:56:20.52.01.55.12.0 Fluxisinunitsof10)]TJ /F4 7.97 Tf 6.59 0 Td[(18Wm)]TJ /F4 7.97 Tf 6.59 0 Td[(2.Apertureradiususedis7pixels.Fluxuncertaintyin-cludescalibrationuncertainty. Table4-2 .IRACcoloranalysisofH2knots. KnotT(103K)NH2(1018cm)]TJ /F4 7.97 Tf 6.58 0 Td[(2) b2.50.23.70.3c2.70.33.70.2d2.50.24.10.2e2.50.22.20.2f2.50.22.60.2g3.20.43.00.1h3.00.70.60.1i3.00.21.10.1j3.30.62.10.1k2.80.32.30.2l3.30.81.30.1m2.50.31.10.2n2.30.22.90.4o2.30.11.50.3p2.80.62.00.2q2.60.12.10.2r4.00.81.40.1 64

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Table 4-2 .Continued. KnotT(103K)NH2(1018cm)]TJ /F4 7.97 Tf 6.58 0 Td[(2) s2.80.61.00.2t2.60.31.00.2u3.30.21.40.1w2.70.22.40.2 Theestimatedtemperatureisthecolumndensityaveragedtemperaturedeterminedfrompixelcolorswithineachaperture.Thetemperatureuncertaintyisthecolumndensityweightedstandarddeviationofthetemperaturescorrespondingtotheindividualpixels. 65

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CHAPTER5MOLECULARHYDROGENEMISSIONSURVEYOFTHEROSETTEMOLECULARCLOUD 5.1BackgroundMasslossintheformofoutowsisubiquitousduringtheearlystagesofstarforma-tion.Theseoutowscanprovideinformationontheaccretionandmasslosshistoryofindividualformingstars( Reipurth&Bally 2001 ).Onglobalscalesoutowscanprovidefeedbackintothecloudandassistinregulatingstarformation.Theoutowscanbetracedbyemissionthatarisesfromshockheatingwhentheoutowinteractswithsurroundinggas.TheRosetteMolecularCloud(RMC)providesanideallayoutinwhichtostudyvariousaspectsofstarformation.Previousstudiesofthecloudhaverevealedthepresenceofoutowactivity.Anopticalnarrow-band[SII]imagingsurveyofthecloudfoundevidenceofshockedgas( Ybarra&Phelps 2004 )anda12COsurveyrevealedseveralmolecularows( Dentetal. 2009 ).Opticalsearchesarelimitedbyextinctionthatispresentinmolecularcloudsandradiosurveysoftenlacktheresolutionneededtodisentangleowsandstudythestructuresindetail.Shockexcitedgascanalsobetracedinthenear-infrared(NIR),inparticular,throughthemolecularhydrogenemission(H2)lines.NIRnarrow-bandH2imagingofthePL06regionby Aspin ( 1998 )revealedtheexistenceofmultiplebowshockssurroundingthecentralAFGL961binary.Afollowupstudyofoneofthe[SII]emissionfeaturesby Phelps&Ybarra ( 2005 )revealaseriesofshockedH2knotsoriginatingfromanembeddedYSOnearclusterPL01.AnunbiasedsearchforH2emissionwithinalltheknownembeddedclustershasnotpreviouslybeendone.Inthispaperwepresenttheresultsofournarrow-bandH2imagingsurveyoftheRMCembeddedclusters.WeuseavailableSpitzerInfraredArrayCamera(IRAC)photometrytodistinguishbetweenshockedandUVexcitedemission.Wediscussthe 66

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correlationbetweentheshockedemissionandtheclustersandalsodiscussthepropertiesofthedrivingsources. 5.2ObservationsandDataReductionNear-Infrared,narrow-bandobservationsoftheRMCembeddedclusterswereobtainedwiththeInfraredSidePort-Imager(ISPI)ontheBlanco4metertelescopeattheCerroTololoInter-AmericanObservatory(CTIO).ISPIemploysa20482048HgCdTeHawaii-2arraywitha10.2510.25arcmineldofviewandaplatescaleof0.30500pixel)]TJ /F4 7.97 Tf 6.59 0 Td[(1.TheeldswereimagedusingaH21S(1)2.122mlter(c=2.126m,==:01)andanarrow-bandcontinuum,Kcont,ltercenteredat2.146m.Theobservationsweretakenduringthenightsof2008December17throughDecember19.Figure 5-1 showstheregionssurveyed(blueboxes)overplottedonagray-scale2MASS1K-bandimageofthecloud.TheFlamingosIIDataPipeline(FATBOY)wasusedtoreducethedata( Warneretal. 2012 ).FirstalinearitycorrectionwasappliedtothedatawiththeknownISPIlin-earizationcoecients2.Flateldingandskysubtractionwerethenapplied.AstrometryoftheindividualframeswasperformedusingSExtractor( Bertin&Arnouts 1996 )andSCAMP( Bertin 2006 ).Distortioncorrection,alignment,andstackingwereperformedwithSWarp( Bertinetal. 2002 ).TheNIRimageswereuxcalibratedtothe2MASSKsbandbydeterminingthemagnitudedierencebetweenthe2MASSKsbandcatalogvaluesandtheISPIimagemagnitudesforstarsincommon. 1ThispublicationmakesuseofdataproductsfromtheTwoMicronAllSkySurvey,whichisajointprojectoftheUniversityofMassachusettsandtheInfraredProcessingandAnalysisCenter,fundedbytheNationalAeronauticsandSpaceAdministrationandtheNationalScienceFoundation2 http://www.ctio.noao.edu/noao/content/ISPI-Linearity-Correction 67

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Figure5-1 .2MASSK-bandimageoftheRMCwithblueboxesindicatingtheregionssurveyedintheH22.12mline. 5.3DistinguishingBetweenShockedandUVExcitedMolecularHydrogenMolecularhydrogenemissionisagoodtracerofshockedgasfromoutows.However,H2emissioncanalsoarisefromUVuorescenceincoldgas( Black&Dalgarno 1976 ; Black&vanDishoeck 1987 ).InthisprocessexternalUVphotonsareabsorbedbyH2intoitsexcitedelectronicLyman(B1+u)andWerner(C1u)bands.Theseexcitedmoleculeswilleitherdecayintothegroundelectronicstatecontinuumanddisassociateordecayintodiscretero-vibrationallevelsofthegroundelectronicstateandthencascadethroughro-vibrationaltransitionsgivingrisetoinfraredphotons.TheresultinglineratiosfromtheH2uorescentemissioncanoftenmimicthoseofshockheatedgas.Inorderto 68

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compileacensusofoutowactivityintheclouditisimportanttobeabletodistinguishbetweenthetwoexcitationmechanisms. Ybarra&Lada ( 2009 )developedamethodofanalyzingshockedH2usingSpitzerIRACphotometry.ThelocationoftheshockedgasinIRACcolorspacewasdeterminedtobeafunctionoftemperature,density,andextinction.InthischapterweexpandthisanalysistoinvestigatetheIRACcolorsofUVexcitedH2withthehopeofbeabletodistinguishbetweenUVandshockexcitedemission.Weusethepopulationofro-vibrationallevelsfrom Sternberg&Neufeld ( 1999 ).Wealsoincludedthepurerotational(=0)levelsj=8throughextrapolationusingTgas=500K.Similarto Ybarra&Lada ( 2009 )weusedtheEinstein-Atransitioncoecients( Wolniewiczetal. 1998 ),IRACspectralresponse( Horaetal. 2008 ),andcalibrationdata( Reachetal. 2005 )tocalculatetheIRACcolors.WecalculatetheIRACcolorsfortheUVexcitedH2emissionfromthemodelof Sternberg&Neufeld ( 1999 )tobe[3:6])]TJ /F6 11.955 Tf 12.53 0 Td[([4:5]=)]TJ /F6 11.955 Tf 9.29 0 Td[(1:2and[4:5])]TJ /F6 11.955 Tf 12.52 0 Td[([5:8]=1:1.Takingintoconsiderationreddening,uncertaintiesintheortho-to-pararatio,andpossiblePAHcontributiontothe5.8mbandwedenethefollowingcriteriaasthecolorspaceofprobableUVexcitedH2: )]TJ /F6 11.955 Tf 11.95 0 Td[(1:2<[3:6])]TJ /F6 11.955 Tf 11.95 0 Td[([4:5]<)]TJ /F6 11.955 Tf 9.3 0 Td[(0:21:1<[4:5])]TJ /F6 11.955 Tf 11.95 0 Td[([5:8]PotentialH2featuresthatfallwithinthiscolorspacewillberemovedfromthecatalogandwillnotusedforthecalculationofoutowluminosities. 5.4Results 5.4.1MolecularhydrogenemissionfeaturesInTable 5-2 wepresentourcensusoftheH2featuresintheRMC.Thelistedcoor-dinatesarethatofthecenteroftheemission.TheuxismeasuredinpixelsforwhichS/N>2.MHOdesignationsrefertotheobjectswhichhaveentriesintheCatalogueof 69

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MolecularHydrogenEmission-LineObjects(MHOs)inOutows3( Davisetal. 2010 ).ThefeatureslistedinourcensusdonotdisplaySpitzerIRACcolorsconsistentwithUVexcitedemissionandthuswecanassumetheemissionisduetoshockedgasfromoutows.Intotalweidentify181individualH2knotsintheRMC.Manyoftheseindividualknotscompriselargescaleoutows. 5.4.2AssociationofoutowactivityandembeddedclustersInthissectionweinvestigatetheassociationofoutowactivitywiththeembeddedclusters.Thefollowingplotsarecomposedoffourpanels:animageoftheregionusingtheH22.12lter,animageofthesameregionwiththeKcont2.15mlter,animageshowingthecontinuumsubtractedpureH2emission,andamapshowingregionswithIRACcolorsconsistentwithUVexciteduorescentH2emission.Theclusterswithinthenebularregion(PL01andPL02)displaymuchdiuseH2emissionwithmorphologyconsistentwiththeopticaledgeofthenebula(Figures 5-2 and 5-3 .IRACcoloranalysisrevealstheprobableexcitationmechanismfortheemissionisUVuorescentexcitation.ThereissomeH2thatcanbeattributedtoshockexcitation.InclusterPL01thereareH2knots(002-004)whichappeartooriginatefromanembeddedClassI/0objectinthecluster.TotheeastoftheclustercenterthereisalsotheHH871outow( Phelps&Ybarra 2005 )alsooriginatingfromaClassI/0object.ClusterPL02displaysverylittleshockedemission;OnlyoneH2emissionfeature(013)isfoundintheclustercenter.ThePL03regioncontainsachainofknots(134-139)NWofthecluster.TheclusteritselfissurroundedbydiuseH2emission(Figure 5-4 ).WendthemajorityofthisemissiontohaveIRACcolorsconsistentwithUVexciteduorescentH2.Thegeometryof 3MHOcatalogueishostedbyLiverpoolJohnMooresUniversity. http://www.astro.ljmu.ac.uk/MHCat/ 70

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Figure5-2 .NIRimagesandUVexcitedH2mapofthePL01clusterregion.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofprobableUVexcitedH2fromIRACcoloranalysis. thediuseUVexcitedemissionsuggeststhatthesourceofUVphotonsisfromwithinthecluster.OurimageofPL06(Figure 5-5 showstheH2knotsrstthatwerediscoveredby Aspin ( 1998 ).Thebrightcenterofthecluster(AFGL961)isoversaturatedintheSpitzerIRACbandimagesandthereforeIRACcoloranalysisisunabletodeterminethenatureoftheH2emissioninthecenter.TheyoungclustersPL07(Figure 5-6 )andREFL08(Figure 5-7 )displaymoreoutowactivitythanmostoftheotherclusters.Thesetwoclustershaveahighfractionofprotostarswhichindicatesyouth( Ybarraetal. 2013 ).TheH2knotsofREFL08are 71

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Figure5-3 .NIRimagesandUVexcitedH2mapofthePL02clusterregion.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofprobableUVexcitedH2fromIRACcoloranalysis. distributedthroughouttheregionandthedistributionisconsistentwithmultipleoutows,withpossibleoverlapofowsalongthelineofsight.PL07containsmultipleH2emissionfeaturespredominantlyinthecenterofthecluster.Manyofthefeaturesappeartotraceoneormoreoutows.ClustersPL04,PL05,andREFL09showsadearthofH2emission(Figures 5-8 5-9 5-10 ).( Wangetal. 2009 )foundaconcentrationofClassIIIsourcesinPL04,and( Ybarraetal. 2013 )foundtheYSOratiosofPL04andPL05tobeconsistentwithagesof2-3Myr,indicatinganolderpopulationofstars.ThelackofH2emissioninREFL09maybe 72

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Figure5-4 .NIRimagesandUVexcitedH2mapofthePL03embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofprobableUVexcitedH2fromIRACcoloranalysis. duetohighextinctionassociatedwiththecluster.However,thismayalsobecorrelatedtothelownumberofprotostarsdetectedinthiscluster.InordertoquantitativelyinvestigatetheamountofamountactivitywithintheembeddedclustersIsummeduptheH2emissionfromtheknotswith1pcoftheclustercentersforeachembeddedcluster.Figure 5-11 showsaplotofsummedH22.12m 73

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Figure5-5 .NIRimagesandUVexcitedH2mapofthePL06embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofregionswithIRACcolorsconsistentwithUVexcitedH2. emissionfromknotsversusnumberofprotostars.TheH2emissionandthenumberofprotostarsaremeasuredwithin1pc(2.140)oftheclustercenters.ClusterPL06isnotplottedasitdisplaysanomalouslystrongH2andduetooversaturationinSpitzerimagingitsprotostarcountisatbestalowerlimit.ThereappearstobearelationshipwhereclusterswithhighernumbersofprotostarshavebrighterH2emission,whichsuggestsmoreoutowenergywithinthecluster.ThePearson'scorrelationcoecientbetweenthesevariablesis0.80.WealsoinvestigatetherelationshipbetweensummedH2emissionandtheratioofprotostarstoClassIIobjects.Figure 5-12 showsaplotofH22.12memissionversustheratioofClassI/0toClassIIsourceswithin1pc(2.140)oftheclustercenters. 74

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Figure5-6 .NIRimagesandUVexcitedH2mapofthePL07embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.Thelocationofbrightknotsareindicated.D)MapofregionswithIRACcolorsconsistentwithUVexcitedH2. Theratioandratiouncertaintywerecalculatedfromtheformulasin Ybarraetal. ( 2013 ).ThePearson'scorrelationcoecientbetweenthesevariablesis0.88.WendthatclusterswithhigherClassI/0toClassIIratiostendtohavemoreH2emission,whichsuggestsoutowactivityisstrongerforyoungerregions.Interestingly,theredoesnotappeartobeacorrelationbetweenH2emissionandtotalluminosityoftheprotostarsintheclusters.Weestimatetheluminosityoftheprotostarswiththemethoddevelopedby Kryukovaetal. ( 2012 ).usingSpitzerIRACandMIPS24 75

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Figure5-7 .NIRimagesandUVexcitedH2mapoftheREFL08embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.Thelocationofbrightknotsareindicated.D)MapofregionswithIRACcolorsconsistentwithUVexcitedH2. mphotometry. Kryukovaetal. ( 2012 )foundthebolometricluminosityofprotostarstobeafunctionoftheirMIRluminosityandslopeoftheirSpectralEnergyDistribution(SED).Figure 5-13 showsaplotofH22.12memissionversustotalluminosityofprotostarswithin1pc(2.140)oftheclustercenters.ThePearson'scorrelationcoecientis-0.003,suggestingaveryweaktonocorrelationbetweenthevariables.Eventhoughasingleobjectcandominatethetotalluminosityofaregion,itisthenumberofsourcesthatappearstobemoreimportanttothetotaloutowactivity. 76

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Figure5-8 .NIRimagesandUVexcitedH2mapofthePL04embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofregionswithIRACcolorsconsistentwithUVexcitedH2. Ybarraetal. ( 2013 )ndevidencethatregionsintheRMCremovegasveryquicklyastheyage.Therelationshipbetweencolumndensityofgasandagewasfoundtohaveahalf-lifeof0.4Myr,whichissimilartothelifetimeofprotostars.Wecomparethistotherelationshipbetweenoutowactivityandageandsuggestthatoutowsplayasignicantroleingasremovalearlyonintheevolutionofacluster. 5.4.3DrivingsourcesManyoftheH2emissionfeaturesarearrangedinlinearstructureswhichallowfortheidenticationofthedrivingsources.InthecenterofclusterPL01wendH2emissionknots(002-004)thatappeartotraceoutaoutoworiginatingfromanembedded 77

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Figure5-9 .NIRimagesandUVexcitedH2mapofthePL05embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofregionswithIRACcolorsconsistentwithUVexcitedH2. protostar(Figure 5-14 ).IntheNIRthesourceappearstohavethemorphologyofareectionnebula,possiblyrevealingacavityformedfromtheoutow.TheoutowsourcehasIRACcolorsofaClassI/0objectandisoneofthebrightestMIPS24msourcesinthecluster.TheotheroutowinthePL01regionisHH871(Figure 5-15 )discoveredby Phelps&Ybarra ( 2005 ).ThisowiscomposedofmanyH2knots(005-010)andappearstooriginatefromaClassI/0object.WithintheyoungclusterREFL08thereisachainofknots(032-036,041,042)whichappeartotraceoutanoutowofpointsymmetryaboutanembeddedMIPS24msource(s4;Figure 5-16 ).Thewesternend(033)oftheoutowappearsequidistanttotheeasternend(042)fromtheproposeddrivingsourcewithan 78

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Figure5-10 .NIRimagesandUVexcitedH2mapoftheREFL09embeddedcluster.A)H22.12mimage.B)Kcont2.15mimage.C)Continuum-subtractedpureH2emissionimage.D)MapofregionswithIRACcolorsconsistentwithUVexcitedH2. angulardistanceof0.650.ClusterPL03containsagroupofH2knots(134-139)thathasthemorphologyofanoutow(Figure 5-17 ).Thisowappearstooriginatefromanembeddedprotostarnorthwestofthecenterofthecluster.InthecenterofclusterPL07(Figure 5-18 )therearetwolinearchainsofH2knotsthatappeartooriginatefromanembeddedClassI/0protostar.Thesemayrepresenttwoseparateowsthatcanoccurinthecaseofabinary,ortheseknotsmaybetracingtheedgesofanoutowcavity. 79

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Figure5-11 .SummedH22.12mlineemissionvs.numberofprotostarswithin1pc(2.140)oftheclustercenters. Table 5-1 liststheproposeddrivingsourcesoftheoutows.Thedrivingsourcesappeartobepredominantlyembeddedprotostars.WhileYSOsthroughClassIIareknowntopoweroutows,studiessuggestoutowsarestrongestduringtheprotostarstage.ThisisconsistentwithouridentiedoutowsourcesandalsothecorrelationbetweentheH2uxandthenumberofprotostarsinaregion. Table5-1 .Outowdrivingsources. IDR.A.Dec.ClassKnots s197.96394.3197I/0002-004s297.98374.3174I/0005-010s398.56094.3444I/0037,038s498.56434.34170032-036,041,042s598.36894.02210134-139 80

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Figure5-12 .SummedH22.12mlineemissionvs.ClassI/0toClassIIratiowithin1pc(2.140)oftheclustercenters. 5.5SummaryWecatalogandinvestigatethedistributionofshockedH2emissionthroughoutthecloud.ThedistributionofshockedH2emissionisnotuniformandthattheemissionap-pearstobemoreprominentinyoungerregions.WeidentifythedrivingsourcesformanyoftheoutowstracedbyH2emissionandndthedrivingsourcesarepredominantlyyoungClassI/0protostars.WendstrongcorrelationsbetweenthetotalmeasuredH2lineemission,numberofprotostars,andratioofprotostarstoClassIIobjects.TherelationshipbetweenthetotalemissionandtheprotostartoClassIIratiosuggestsyoungerclustershavemoreoutowactivity,andthatoutowactivityintheRMCdecreaseswithage.Wecomparethistotherelationshipbetweenageandextinctionfrom Ybarraetal. ( 2013 )andsuggestoutowplayasignicantroleinthegasremovalwithintheclustersandsubsequentlyaectingclusterandmolecularcloudevolution. 81

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Figure5-13 .SummedH22.12mlineemissionvs.totalluminosityofprotostarswithin1pc(2.140)oftheclustercenters. Figure5-14 .NIRH2andSpitzerimagesofanoutowinPL01.A)H22.12mimage.Theredcrossindicatestheproposeddrivingsource.B)IRAC4.5mimage.C)MIPS24mimage. 82

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Figure5-15 .NIRH2andSpitzerimagesofoutowHH871(005-010)inPL01.A)H22.12mimage.Theredcrossindicatestheproposeddrivingsource.B)IRAC4.5mimage.C)MIPS24mimage. Figure5-16 .NIRH2andSpitzerimagesofoutowsinREFL08.A)H22.12mimage.Theredcrossesindicateproposeddrivingsources.B)IRAC4.5mimage.C)MIPS24mimage. 83

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Figure5-17 .NIRH2andSpitzerimagesofanoutowinPL03.A)H22.12mimage.B)IRAC4.5mimage.C)MIPS24mimage. Figure5-18 .NIRH2andSpitzerimagesofthecenterofclusterPL07.A)H2(2.12m)image.RedcontoursrevealthepureH2emission.Theredcrossindicatesthelocationoftheproposeddrivingsource,adeeplyembeddedprotostar.B)IRAC4.5mimage.C)MIPS24mimage. 84

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Table5-2 .ListofH2emissionfeatures. IDR.A.Dec.FluxAreaOtherID(10)]TJ /F4 7.97 Tf 6.59 0 Td[(4Jy)(pixels) 197.92424.30322.40.237297.96224.32043.90.242397.96474.319621.50.4208497.96474.31882.80.230MHO1361597.98434.31763.40.233HH871;MHO1360697.98594.31861.00.112HH871;MHO1360797.98594.31784.00.231HH871;MHO1360897.98644.31847.90.248HH871;MHO1360997.98684.31941.70.124HH871;MHO13601097.98764.31906.90.257HH871;MHO13601198.28954.63641.30.1221298.29024.63621.50.1231398.30854.57972.90.2511498.31564.53631.90.1121598.31634.53637.70.2491698.32404.53864.60.2551798.32454.53760.90.1171898.32644.53870.90.1141998.29244.51451.80.1312098.28864.50920.80.1152198.27784.49923.00.1432298.49154.33574.60.2612398.49884.34531.50.1262498.52084.33921.30.1212598.52044.33772.10.133MHO13742698.52004.32941.30.1192798.52854.32494.10.2432898.54194.37563.60.2532998.55034.36141.20.117MHO13733098.55124.36101.80.129MHO13733198.55474.38070.50.173298.54784.34430.50.193398.54854.34462.20.1333498.55044.34300.70.1133598.55104.34270.50.193698.55664.34202.00.130MHO13703798.55864.339312.60.393MHO13723898.55934.34074.80.255MHO13723998.56194.34291.00.119 85

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Table 5-2 .Continued. IDR.A.Dec.FluxAreaOtherID(10)]TJ /F4 7.97 Tf 6.59 0 Td[(4Jy)(pixels) 4098.56284.34260.80.1134198.56974.33983.10.241MHO13714298.57014.34089.90.396MHO13714398.57374.33010.70.1114498.58434.35311.50.120MHO13694598.58644.34880.70.1114698.58884.34920.80.113MHO13684798.58944.34851.20.116MHO13684898.59014.34521.10.1164998.58984.30883.30.244MHO13675098.59194.31081.60.1235198.59324.31071.60.1255298.59734.31151.10.1175398.54274.29661.60.1265498.51624.27982.70.2415598.58764.19341.90.1325698.63114.22640.50.175798.63244.22310.60.1115898.63384.22140.90.1135998.63454.22196.60.2656098.62534.18721.40.1256198.63974.19121.40.1236298.63984.19181.10.1176398.65124.19429.20.2466498.65114.19486.20.2446598.65204.194214.80.3896698.64904.201712.60.31606798.65024.202215.70.41896898.64964.20363.80.2516998.64964.20800.90.1157098.65044.20821.20.1207198.65064.2092120.31207298.65434.207168.30.63397398.65614.20661390.84297498.65584.20821.90.1207598.65114.22347.50.3987698.65164.21980.50.187798.65194.21932.50.2347898.65454.21732.90.1197998.65504.21772.50.116 86

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Table 5-2 .Continued. IDR.A.Dec.FluxAreaOtherID(10)]TJ /F4 7.97 Tf 6.58 0 Td[(4Jy)(pixels) 8098.65584.21697.60.3868198.65654.21651.50.1198298.65364.22075.90.2538398.65434.22063.70.2358498.65384.21921.80.1288598.65514.21931.10.1148698.65564.21994.40.2448798.65574.21895.60.2568898.65494.22295.80.2408998.65554.222316.90.3969098.65654.221420.80.41349198.65704.220412.60.3649298.65674.21962.60.1249398.65684.21841.40.1149498.65664.21801.20.1139598.65894.22201.80.1219698.65954.22082.00.1169798.65984.22148.80.2649898.65944.22011.60.1169998.66004.22054.90.23610098.66074.22151.80.11610198.66034.21971.80.11610298.66074.220310.80.35810398.66454.22434.40.25410498.66454.22360.70.11110598.66504.22341.10.11410698.66594.22870.40.1610798.66774.22960.40.1810898.66814.22960.50.1810998.66814.22920.60.11111098.66954.22950.50.1911198.67114.23730.70.11011298.67234.23695.00.26511398.67334.236510.70.39911498.68324.24540.90.11511598.68544.24102.90.23311698.68604.24081.00.11411798.68654.24040.60.1911898.68794.24320.50.1711998.68864.24330.60.110 87

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Table 5-2 .Continued. IDR.A.Dec.FluxAreaOtherID(10)]TJ /F4 7.97 Tf 6.58 0 Td[(4Jy)(pixels) 12098.68864.24200.50.1712198.64704.15131.60.12112298.65774.13210.80.11312398.66254.13041.70.12612498.66334.13000.70.11012598.66314.12960.70.1912698.66394.12970.70.11012798.66444.12970.50.1812898.66454.12930.90.11212998.66394.12890.60.1813098.67094.12580.80.11013198.67274.12601.70.12013298.68504.11913.90.24113398.33284.00732.00.13013498.36504.02771.20.11813598.36564.02750.80.11313698.36564.02641.10.11413798.36564.02602.10.11613898.36614.02612.90.12313998.36744.02165.10.24614098.36854.00980.60.11114198.85694.01713.50.25614298.85724.01601.30.11814398.84934.00561.50.12614498.85464.00661.70.12914598.88594.01190.50.1914698.88464.00460.50.1814798.88414.00421.00.11714898.87683.98684.50.23914998.87743.98662.80.13815098.87873.98530.70.11015198.87933.98510.60.11015298.87983.98680.60.1815398.88133.98551.20.12015498.88193.98470.70.11315598.87913.98162.10.12315698.88043.98312.80.11615798.88083.98312.40.11615898.88053.98274.70.22415998.88133.98224.90.236 88

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Table 5-2 .Continued. IDR.A.Dec.FluxAreaOtherID(10)]TJ /F4 7.97 Tf 6.58 0 Td[(4Jy)(pixels) 16098.88153.98160.80.11316198.88293.98222.90.13716298.88283.98140.50.1916398.88303.98090.60.11116498.88343.98090.60.11016598.88393.98041.50.12016698.87923.97223.00.13516798.87753.96390.50.11016898.87813.96350.60.11216998.88453.96580.90.11317098.88463.96540.40.1617198.88243.95927.40.25117298.89093.97751.20.12017398.89203.97533.30.12817498.89213.97480.40.1617598.89223.97450.80.11117698.89263.97431.10.11517798.89333.97130.70.11017898.89723.96070.60.1917998.89783.96105.10.24318098.87923.95110.50.1918198.86003.95000.50.110 89

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CHAPTER6CONCLUSIONThisstudyusedobservationsoftheRosetteMolecularCloud(RMC)inordertoelucidatetheconnectionsbetweenthestarformationinembeddedclustersandtheevolutionofamolecularcloud.InChapter2,Iusedmid-infraredobservationsfromtheSpitzerSpaceTelescope,X-rayobservationsfromtheChandraX-rayObservatory,andFLAMINGOSphotometrycatalogdatatoinvestigatethedistributionsofyoungstellarobjects(YSOs)andgaswithintheRMC.TheYSOsweredierentiatedintotheirevolutionaryclassesandthedensitydistributionsofthedierentclasseswerestudied.IdevelopedatechniqueusingYSOratiostostudyagegradientsacrossthecloudtobetterunderstandhowstarformationhasprogressed.RelationshipsbetweentheYSOratiosandextinctionwerefoundthatsuggestedstarformationinthecloudoccurspreferentiallyinhighextinctionregionsandthatthecolumndensityofgasrapidlydecreasesastheregionevolves.Isuggestrapidremovalofgasmayaccountforthelowstarformationecienciesobservedinmolecularclouds.Theobservationssuggestthatthe[HII]regionproducedbytheOBclusterNGC2244haslittletonoeectontherelativeagesoftheembeddedclusters.Theseobservationsthusshedlightonhowstarformationprogressesthroughmolecularclouds.Inadditiontoexternallyinducedenvironmentalconditions,clusterevolutionmaybeeectedbyoutowsfromtheformingstars.Protostellaroutowscanbetracedbyemissionfromshockheatedgas.InChapter3,IdescribedatechniqueIdevelopedtoidentifyprobableregionsofshockedgasusingimagingdatafromtheSpitzerInfraRedArrayCamera(IRAC).ThelocationofshockedH2inIRACcolorspacedependsonitstemperatureandthereforcoloranalysiscanprovideanewwaytoprobethethermalstructureofthegas.InChapter4,IusedtheSpitzerIRACobservationsalongwithnarrow-bandnear-infraredH2observationstostudyabrightparsecscaleoutowintheRosette.Themorphologyandthermalstructureoftheoutowsuggeststhattheoutow 90

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interactswiththesurroundingdensematerialcausingdeectionandpossiblydecelerationoftheoutowingmaterial.InChapter5,IpresentasurveyforshockedH2emissionintheRMCembeddedclustersandinvestigatethespatialdistributionoftheemission.ThedistributionofshockedH2emissionwasfoundtonon-uniformwiththeemissionappearingmoreprominentinyoungerregions.IcomparetheoutowactivitytracedbyH2withnumberofprotostarsincluster,theratioofprotostarstoClassIIobjects,andtotalluminosityoftheprotostars.Indpositivelinearcorrelationsbetweentheemissionandnumberofprotostars,andalsobetweentheemissionandClassI/0toClassIIratio.Therelationshipbetweenoutowactivityandageandsuggestthatoutowsplayasignicantroleingasremovalearlyonintheevolutionofaclusterandpossiblydrivingthetheprogressionofstarformationwithinthecloud. 6.1FutureDirectionsInthisstudywesuccessfullyusedYSOratiostostudyagegradientsintheRMCandlearnhowstarformationmightbeprogressing.TherearesomelimitationstoratioageestimationssuchaslargeuncertaintiesinherenttoratiosofPoissonprocessesandpossiblemassdependencetodisklifetimes.ThusYSOratiosarebettersuitedtomappingagegradientsthandeterminingabsoluteages.Muchmoremaybelearnedusingspectroscopicallydeterminedages.Onlargescales,clusteragescanbeusedwithluminosityfunctionstoconstructinitialmassfunctions(IMFs).Integratingthemassfunctionscanprovidetheclusterstotalstellarmasscontentandcanbeusedtodeterminestarformationratesandeciencies.Onsmallerscales,spectroscopicallydeterminedagescombinedwithYSOevolutionaryclassinformationcanbeusedtostudythepossiblevariationsofdisklifetimesasafunctionofenvironment,whichcouldconstrainplanetformation.Ihavereduced13platesfromFLAMINGOSmulti-objectspectraobservationsoftheRMCclusters.Iplantousethespectroscopytoclassifythestellarcompositionoftheclusters.ExistingFLAMINGOSphotometrywillbeusedtomeasuretheluminosityofthe 91

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stars.FromthereeachclustermembercanbeplacedonanH-Rdiagram.ThelocationofthestarsontheH-RdiagramwillbecomparedtoPMSevolutionarymodelstoobtainamedianageforeachcluster.AK-bandluminosityfunction(KLF)canthenbeconstructedfromdeepNIRimagingdata.Anembeddedcluster'sKLFisafunctionofitsIMFandage-dependentmass-luminosityrelation.UsingthespectroscopicallyderivedageoftheclusterandPMStracks,asuiteofmodelluminosityfunctionscanbecreatedasafunctionofanunderlyingIMF.AbesttbetweentheclusterKLFandmodelKLFwillbeusedtoderivetheclusterIMF( Muenchetal. 2003 ).ThetotalclustermassiscalculatedthroughintegrationoftheIMF.Thestarformationratecanthenbecalculatedbydividingthetotalclustermassbythemedianageofthecluster.Thestarformationeciencyisobtainedbycomparingtheclustermasstothemassoftheassociatedmolecularcore.IwillinvestigatehowandifthesepropertiesvarywithlocationandthusenvironmentwithintheRMC. 92

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BIOGRAPHICALSKETCH Jasonhadarelativelyuneventfulchildhood.Inthefallof1999heandhisfriend,Mr.Dave,survivedanattackfromelephantsealbullswhilewanderingthroughAnoNuevoStatebeach-atnight-duringelephantsealmatingseason.Jasonwasacollegedropoutforafewyears(2000-2002).HeenrolledinSacramentoStateandgraduatedwithaB.S.inphysicswithanastronomyminor.HethenenrolledinthephysicsmastersprogramatSanFranciscoStateUniversity.ThereheresearchedoutowsinrhoOphiuchusundertheguidanceofDr.MaryBarsony.AfterrecievinghisM.S.inPhysics,hereturnedtoSacramentoStateandtaughtastronomyclassesforayear.In2007hemovedacrosscountryandenrolledintheAstronomyPh.D.programattheUniversityofFlorida.HewasawardedaFloridaSpaceGrantfellowshipandaNASAGSRPfellowshipthroughGoddardSpaceFlightCenter.After6longyears,JasonnallyreceivedhisPh.D.fromtheUniversityofFloridainsummerof2013. 97