Gemini Spectroscopic Survey of Young Star Clusters in MergingInteracting Galaxies. II. NGC

Gemini Spectroscopic Survey of Young Star Clusters in MergingInteracting Galaxies. II. NGC 3256 Clusters

GeminiSpectroscopicSurveyofYoungStarClustersinMerging/InteractingGalaxies.II.NGC3256Clusters

GelysTrancho

arXiv:0704.2577v1 [astro-ph] 19 Apr 2007

UniversidaddeLaLaguna,Tenerife,CanaryIsland,SpainGeminiObservatory,670N.A’ohokuPlace,Hilo,HI96720,USA

gtrancho@gemini.edu

NateBastian

DepartmentofPhysicsandAstronomy,UniversityCollegeLondon,GowerStreet,London,WC1E6BT,

UnitedKingdom

BryanW.Miller

GeminiObservatory,Casilla603,LaSerena,Chile

and

Fran¸coisSchweizer

CarnegieObservatories,813SantaBarbaraStreet,Pasadena,CA91101-1292,USA

ABSTRACT

WepresentGeminiopticalspectroscopyof23youngstarclustersinNGC3256.We ndthat

theclusteragesrangearefromfewMyrto～150Myr.Alltheseclustersarerelativelymassive(2–40)×105M⊙andappeartobeofroughly1.5Z⊙metallicity.Themajorityoftheclustersinoursamplefollowthesamerotationcurveasthegasandhencewerepresumablyformedinthemolecular-gasdisk.However,awesternsubsampleof veclustershasvelocitiesthatdeviatesigni cantlyfromthegasrotationcurve.Theseclustersmayeitherbelongtothesecondspiralgalaxyofthemergerormayhaveformedintidal-tailgasfallingbackintothesystem.Wediscussourobservationsinlightofotherknownclusterpopulationsinmerginggalaxies,andsuggestthatNGC3256issimilartoArp220,andhencemaybecomeanUltra-luminousInfraredGalaxyasthemergerprogressesandthestar-formationrateincreases.

Someoftheclusterswhichappearedasisolatedinourground-basedimagesareclearlyresolvedintomultiplesub-componentsintheHST-ACSimages.Thesamee ecthasbeenobservedintheAntennaegalaxies,showingthatclustersareoftennotformedinisolation,butinsteadtendtoforminlargergroupsorclustercomplexes

Subjectheadings:globularclusters:general—globularclusters:individual(NGC3256)

1.Introduction

Intheprevailingpictureofhierarchicalearly-type-galaxyformation,smallfragmentsform rstandthenmergeintolargerandlargerpiecesuntilthesystemresemblesalarge,smooth,anisotrop-icallysupportedellipticalgalaxy.Thestudyofglobularclustershasanimportantroletoplayintestingthepredictionsofthistheoryandinan-sweringthequestionaboutifandwhenthebulkofthismergingtookplace.StudiesoftheGalactic

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