To appear in The Astrophysical Journal (Letters) Dynamical Evidence for a Luminous, Young G

Recent high-resolution observations with the Hubble Space Telescope (HST) reveal that star clusters of extraordinary luminosity and compactness are commonly found in a variety of starburst systems. There has been much speculation that these clusters repres

ToappearinTheAstrophysicalJournal(Letters)

DynamicalEvidenceforaLuminous,YoungGlobularClusterinNGC1569

LuisC.Ho

Harvard-SmithsonianCenterforAstrophysics,Cambridge,MA02138

and

AlexeiV.Filippenko

DepartmentofAstronomy,UniversityofCalifornia,Berkeley,CA94720-3411

ABSTRACT

Recenthigh-resolutionobservationswiththeHubbleSpaceTelescope(HST)reveal

thatstarclustersofextraordinaryluminosityandcompactnessarecommonlyfoundin

avarietyofstarburstsystems.Therehasbeenmuchspeculationthattheseclusters

representpresent-dayanalogsofyoungglobularclusters.UsingtheHIRESechelle

spectrographontheKeck10mtelescope,weobtainedhigh-dispersionopticalspectra

ofoneofthe“superstarclusters”(cluster“A”)inthenearbydwarfgalaxyNGC1569.ThesizeoftheclusterisknownfrompublishedHSTimages.Theline-of-sightvelocitydispersion(σ =15.7±1.5kms 1)hasbeenmeasuredfromacross-correlationanalysisofitsintegratedspectrumatvisualwavelengths.Iftheclusterisgravitationallybound

andthevelocitiesareisotropic,applicationofthevirialtheoremimpliesthatthe

clusterhasatotalstellarmassof(3.3±0.5)×105M .Thisobject’smass,massdensity,

andprobablemass-to-lightratioafteraging10–15Gyrarefullyconsistentwiththe

typicalvaluesofGalacticglobularclusters.Ourresultstronglysuggeststhatatleast

someoftheluminous,compact,youngstarclustersbeingdiscoveredwithHSTwill

indeedevolveintonormalglobularclustersofthetypeseenintheMilkyWay.1

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

starburst—galaxies:starclusters—globularclusters:general

1.Introduction

Inthelastfewyears,HubbleSpaceTelescope(HST)imagingstudiesofavarietyofextragalacticstar-formingsystemshaveidenti edawidespreadnewclassofstarclusters.The1BasedonobservationsobtainedattheW.M.KeckObservatory.

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