We present a detailed analysis of the spectroscopic catalog of galaxies in 10 distant clusters from Dressler et al. (1999, D99). We investigate the nature of the different spectral classes defined by D99 including star forming, post-starburst and passive g

Received:November30,1998;Revised:January18,1999

APreprinttypesetusingLTEXstyleemulateapj

THESTARFORMATIONHISTORIESOFGALAXIESINDISTANTCLUSTERS1

BiancaM.Poggianti,2,3,4IanSmail,5AlanDressler,6WarrickJ.Couch,7AmyJ.Barger,8

HarveyButcher,9RichardS.Ellis,2&AugustusOemler,Jr.6

2)InstituteofAstronomy,MadingleyRd,CambridgeCB3OHA,UK3)RoyalGreenwichObservatory,MadingleyRd,CambridgeCB30EZ,UK

4)OsservatorioAstronomicodiPadova,vicolodell’Osservatorio5,35122Padova,Italy5)DepartmentofPhysics,UniversityofDurham,SouthRd,DurhamDH13LE,UK

6)TheObservatoriesoftheCarnegieInstitutionofWashington,813SantaBarbaraSt.,Pasadena,CA91101-1292

7)SchoolofPhysics,UniversityofNewSouthWales,Sydney2052,Australia

8)InstituteforAstronomy,UniversityofHawaii,2680WoodlawnDr.,Honolulu,HI96822

9)NFRA,POBox2,7990AADwingeloo,TheNetherlands

arXiv:astro-ph/9901264v1 20 Jan 1999

Received:November30,1998;Revised:January18,1999

ABSTRACT

Wepresentadetailedanalysisofthespectroscopiccatalogofgalaxiesin10distantclustersfromDressleretal.(1999,D99).Weinvestigatethenatureofthedi erentspectralclassesde nedbyD99includingstarforming,post–starburstandpassivegalaxypopulations,andreproducetheirbasicpropertiesusingourspectralsynthesismodel.Weattempttoidentifytheevolutionarypathwaysbetweenthevariousspectralclassesinordertosearchfortheprogenitorsofthenumerouspost–starburstgalaxies.ThecomparisonofthespectraofthedistantgalaxypopulationswithsamplesdrawnfromthelocalUniverseleadsustoidentifyasigni cantpopulationofdust–enshroudedstarburstgalaxies,showingbothstrongBalmerabsorptionandrelativelymodest[OII]emission,thatwebelievearethemostlikelyprogenitorsofthepost–starburstpopulation.Wepresentthedi erencesbetweenthe eldandclustergalaxiesatz=0.4–0.5.Wethencomparethespectralandthemorphologicalpropertiesofthedistantclustergalaxies,exploringtheconnectionbetweenthequenchingofstarformationinferredfromthespectraandthestrongevolutionoftheS0populationdiscussedbyDressleretal.(1997).Weconcludethateithertwodi erenttimescalesand/ortwodi erentphysicalprocessesareresponsibleforthespectralandthemorphologicaltransformation.

Subjectheadings:cosmology:observations—galaxies:clusters:general—galaxies:evolution—infrared:

galaxies

1.INTRODUCTION

Ofalltheenvironmentsexploredlocally,thedense,concen-tratedcoresofrichclustersarehighlyconspicuousfortheirlackofstar-forminggalaxies.ThusitcameasasurprisewhenButcher&Oemler(1978;seealsoButcher&Oemler1984)dis-coveredapopulationofblue,possiblystar-forming,galaxiesinthecoresofrichclustersatz>～0.2.Subsequentlowandintermediateresolutionspectroscopyofthesegalaxieshascon- rmedtheyareclustermembersandalsothatstarformationisthecauseoftheirbluecolors(Dressler&Gunn1982,1983,1992;Lavery&Henry1986,1988;Couch&Sharples1987,CS87;Henry&Lavery1987;Soucailetal.1988;Fabricantetal.1991,1994;Couchetal.1994,1998;Abrahametal.1996;Fisheretal.1998).

Whilethevariationinthebluepopulationwithinrichclus-tersshowsevidencefordramaticevolutionarye ects,addi-tionalsignsofchangewerealsouncoveredbythespectroscopicstudies.Theseincludedaclassofgalaxies, rstidenti edbyDressler&Gunn(1983),withnodetectableemissionlines(andhencelittleornoon-goingstarformation)butverystrongBalmerabsorption.Dressler&GunninferredthepresenceofasubstantialpopulationofAstarsandconcludedthatanepochofstrongstarformationhadabruptlyendedintherecentpast,leavingthegalaxyinaso–called‘post-starburst’phase.In1987Couch&Sharplesmadethe rstattempttosynthesiseacoherentviewofthestarformationhistoriesoftheseandtheotherspectralpopulationswithintheclusters,hopingtoiden-tifyasingleevolutionarycyclethroughastarburstphasetothepost-starburstgalaxiesandfromthereintothelargepop-ulationofpassivegalaxiesseenintheclusters(seealsoBarger

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etal.1996).However,thenatureofthephysicalprocess(es)responsiblefortriggeringandterminatingtheepisodesofstarformationinthedistantclusters(andthelackofsuchactivitytoday)hasremainedelusive.

ThenextmajorstepcamefromhighresolutionimagingwiththeHubbleSpaceTelescope(HST).Usingpre-andpost-refurbishmentimaging,thepopulationsofstar-formingandpost-starburstgalaxiesweremorphologicalidenti edwithdisk-dominatedsystems,afractionofwhichareinteractingorob-viouslydisturbed(Couchetal.1994,1998;Dressleretal.1994;Oemleretal.1997).Thissupportedthesuggestionofgalaxy-galaxyinteractionsasonetriggeringmechanismforthestarformationseeninthedistantclusters(Lavery&Henry1988).However,theexpectationthatthehigh-speedencoun-terswithinclusterswouldbeine ectiveatdisturbinggalaxieshasledtootherdynamicalmechanismsbeingsuggested,in-cludingtidaldisruption(Byrd&Valtonen1990)andrepeatedhigh–speedencountersintheclusterpotential(‘harassment’,Mooreetal.1996,1998).Interactionswiththeintraclustermedium(ICM)havealsoremainedapopularexplanationofsomeofthepropertiesoftheButcher-Oemlerpopulation(Gunn&Gott1972).

TheHSTimagingofdistantclustersalsoturnedupevidenceforevolutioninthepassiveclustergalaxies.Thepopulationofluminousclusterellipticalsappeartohavebeeninplaceintheclusterssinceatleastz～0.6(Smailetal.1997)andtheho-mogeneityoftheirpropertieswouldarguethattheyunderwentthebulkoftheirstarformationpriortoz～3(Bower,Lucey&Ellis1992;vanDokkum&Franx1996;Ellisetal.1997;Bargeretal.1998).Incontrast,theS0galaxieswhichdominatethecoresofrichclusterstodayarenoticeablyabsentfromthese

onobservationsobtainedwiththeNASA/ESAHubbleSpaceTelescopewhichisoperatedbySTSCIfortheAssociationofUniversities

forResearchinAstronomy,Inc.,underNASAcontractNAS5-26555.

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