The Starburst-Interstellar Medium Interaction of NGC 1569 I.

We present the detection of He II sources in the Im galaxy NGC 1569 from HST WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The

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aTheStarburst-InterstellarMediumInteractioninNGC1569I.LocationandNatureofHeiiSourcesUsingHubbleSpaceTelescopeWFPC2Imagery1BrentA.BuckalewandReginaldJ.DufourRiceUniversity,DepartmentofSpacePhysics&Astronomy,Houston,TX77025,USAEmail:brent@regultra.rice.edu,rjd@rice.eduandPatrickL.ShopbellCaliforniaInstituteofTechnology,DepartmentofAstronomy,MC105-24Pasadena,CA91125,USAEmail:pls@astro.caltech.eduandDonaldK.WalterSouthCarolinaStateUniversity,DepartmentofPhysicalSciences,Orangeburg,SC29117,USA

Email:dkw@physics.scsu.eduReceived

We present the detection of He II sources in the Im galaxy NGC 1569 from HST WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The

ABSTRACT

WepresentthedetectionofHeiisourcesintheImgalaxyNGC1569from

HSTWFPC2imagery.Outofthe fteendetections,sevenwereWolf-Rayetstars, vewerestellarclusterswithassociatedHeiiemission,andthreeweresourcesofunknownorigin.ThedetectedWolf-Rayetstars’colorsandmagnitudesaresimilartoLargeMagellanicCloudlate-typeWNstars.ThephysicaloriginoftheotherHeiisourcesarediscussed.Weconcludethattheequivalentof51±19WNLstarshavebeendetectedinNGC1569,andwehaveestimatedthetotalWolf-RayetpopulationinNGC1569as78±51.ThesenumbersarecomparedwiththeWolf-RayetstellarpopulationsintheSMC,LMC,MilkyWay,andotherstarburstgalaxiesrelativetotheirluminosities,dynamicalmasses,andionizedgasmasses.

Previoustothisstudy,Wolf-RayetstarsinNGC1569werenotdetectedusing

ground-basedimagery,butwereonlyindicatedthroughlongslitspectroscopy.Thisisthe rsttimetheexactlocationsoftheWolf-Rayetstarsinthisnearby,well-studied,“post-starburst”galaxyhavebeendetermined.

Subjectheadings:galaxies:individual(NGC1569)—galaxies:stellarcontent

—stars:Wolf-Rayet

1.Introduction

EvidenceoflargenumbersofWolf-Rayet(WR)starsingalaxiesservesasatracerofrecentstarbursts.ThelocationsofWRstarsindicatewherestarformationoccurred 10MyragoandwhereOBstarsofmass 20M⊙evolvedtothisstate(e.g.,Schaereretal.1999andreferencestherein).Fromthenumbersandlocationsofsuchstars,one

We present the detection of He II sources in the Im galaxy NGC 1569 from HST WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The

candeterminethestarburstpropertiesandcanstudythekinematicalandmorphologicalimpactthestarbursthasontheinterstellarmedium(ISM).Suchstudiesareparticularlyimportantindwarfirregulargalaxiesbecauseoftheirlowescapevelocity(～100kms 1;Drissen,Roy,&Mo at1993).Becausestarburstgalaxieshavelargestarformationrates(e.g.,logΣSFR≈ 0.8M⊙yr 1kpc 2;Kennicutt1998),thenumberofmassivestarsisenhanced.WiththedetectionofmassiveWRstarsinthesedisturbedsystems,itispossibletocorrelatethemorphologyofthegas(bothHiandHii)andtherecentstarformationhistory.

NGC1569isanearby(D=2.2±0.6Mpc;Israel1988)Imgalaxythathasbeenwell-studiedoverthelast20years.Twoprominent,stellar-likefeaturesarelocatedatthecenterofthisgalaxy,whicharethoughttobesuper-starclusters(SSCs;cf.Prada,Greve,&McKeith1994)formedinastarburst2-10Myrago(Gonz´alez-Delgadoetal.1997).Itisspeculatedthattheywillevolveintoglobularclusters.RecentresultssuggestthatSSCAistwostellarclusterssuperimposedononeanother(DeMarchietal.1997).Identifying45clusterswithinNGC1569,Hunteretal.(2000)determinedtheirageswhichrangefrom2Myrto1Gyr,andtheyfoundasubconcentrationofclusters,includingSSCA,hadanageof4-5Myrold.

FrommultiwavelengthstudiesthegaseousmorphologyofNGC1569showsevidenceofhighsupernovaeactivity.Severalstudiesusingopticalinterference- lterimageryoftheionizedgasshowevidenceofaneruptiveeventwhichoccurredinthegalaxy’spast(Hodge1974;deVaucouleurs,deVaucouleurs,&Pence1974;Waller1991;Hunter,Hawley,&Gallagher1993;Devost,Roy,&Drissen1997).KinematicsoftheionizedgasthatwerestudiedbyTomita,Outa,&Saitou(1994)showedtheexpandinggasmovesatspeedsfrom10to100kms 1.Heckmanetal.(1995)foundthattheoptical lamentsatdistancesof2kpcfromthecenterofthegalaxyaretravelingover200kms 1.Intheinfrared,

We present the detection of He II sources in the Im galaxy NGC 1569 from HST WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The

Hunteretal.(1989)observedthedustradiatingwarmerat60-155µm,whichisexplainedbythestarburst’sstrongradiation eld,thandustinsimilar,irregulargalaxies.Radioobservationsalsoshowrelicsoftheeruptivestarburst.Israel&deBruyn(1988)deducedahighfrequencycuto at8±1GHz,whichtheyattributedtoadecreaseinrelativisticelectroninjectionabout5Myrago.ObservationsofHI(Reakes1980;Israel&vanDriel1990;Stil&Israel1998)revealedthatthedistributionofneutralhydrogenisaclumpyridgeordisksurroundedbyarmswhichmimictheHαarmsseenintheoptical.AnHIholewasdetectedsurroundingtheSSCsandwasformedafterthestarburst(Israel&vanDriel1990).ThedistributionoftheglobalCOemissionissimilartotheHIdistribution(Young,Gallagher,&Hunter1984).HighresolutionCOmapsshowlarge(comparedtoonesintheGalaxy)giantmolecularcloudssurroundingtheSSCAHIhole(Tayloretal.1999).Finally,ROSATPSPCandHRIimagesshowanextendedsoftX-raycomponentperpendiculartothemajoraxisofthegalaxy(Heckmanetal.1995;Stevens&Strickland1998).ASCAimagesofahardX-raysourceinsid …… 此处隐藏：5703字，全部文档内容请下载后查看。喜欢就下载吧 ……