The survival of dark matter halos in the cluster C

arXiv:0711.4587v1[astro-ph]28Nov2007ThesurvivalofdarkmatterhalosintheclusterCl0024+16PriyamvadaNatarajan,1,2Jean-PaulKneib,3IanSmail,4TommasoTreu,5RichardEllis,6SeanMoran,6MarceauLimousin7&OliverCzoske81DepartmentofPhysics,YaleUniversity,P.O.Box208120,NewHaven,CT06520-8120,USA2DepartmentofAstronomy,YaleUniversity,P.O.Box208101,NewHaven,CT06520-8101,USA3ObservatoireAstronomiqueDeMarseilleProvence,Marseille,France4InstituteforComputationalCosmology,DurhamUniversity,SouthRoad,DurhamDH13LE,UK5DepartmentofPhysics,UniversityofCalifornia,SantaBarbara,CA93106-9530,USA6DepartmentofAstronomy,Caltech,1200EastCaliforniaBlvd.,Pasadena,CA91125,USA7DarkCosmologyCentre,NielsBohrInstitute,UniversityofCopenhagen,JulianeMariesVej30,DK-2100Copenhagen,Denmark8KapteynAstronomicalInstitute,P.O.Box800,9700AVGroningen,TheNetherlandsABSTRACTTheoriesofstructureformationinacolddarkmatterdominatedUniversepredictthatmassiveclustersofgalaxiesassemblefromthehierarchicalmergingoflowermasssubhalos.ExploitingstrongandweakgravitationallensingsignalsinferredfrompanoramicHubbleSpaceTelescopeimagingdata,wepresentahighresolutionreconstructionofthemassdistributioninthemassive,lensingclusterCl0024+16atz=0.39.Applyinggalaxy-galaxylensingtechniqueswetrackthefateofdarkmattersubhalosasafunctionofcluster-centricradiusoutto5Mpc,wellbeyondthevirialradius.Wereportthefirstdetectionofthestatisticallens-ingsignalofdarkmattersubhalosassociatedwithlate-typegalaxiesinclusters.ThemassofafiducialdarkmatterhalothathostsanearlytypeL∗galaxyvariesfromM=6.3+2.7−2.0×1011M⊙withinr0.6Mpc,1.3+0.8−0.6×1012M⊙withinr2.9MpcandincreasesfurthertoM=3.7+1.4−1.1×1012M⊙intheoutskirts.ThemassofatypicaldarkmattersubhalothathostsanL∗galaxyincreaseswithcluster-centricradiusinlinewithexpectationsfromthetidalstrippinghy-pothesis.Themassofadarkmattersubhalothathostsalate-typeL∗galaxyis1.06+0.52−0.41×1012M⊙.Early-typegalaxiesappeartobehostedonaverageinmoremassivedarkmattersubhaloscomparedtolate-typegalaxies.Early-typegalaxiesalsotracetheoverallmassdistributionoftheclusterwhereaslate-typegalaxiesarebiasedtracers.Weinterpretourfindingsasevidencefortheactive–2–assemblyofmassviatidalstrippingingalaxyclusters.Themassfunctionofdarkmattersubhalosasafunctionofcluster-centricradius,iscomparedwithanequivalentmassfunctionderivedfromclustersintheMilleniumRunsimulationpopulatedwithgalaxiesusingsemi-analyticmodels.Theshapeoftheobserva-tionallydeterminedmassfunctionsbasedonanI-bandselectedsampleofclustermembersandlensingdataareinverygoodagreementwiththeshapesofthesubhalomassfunctionsderivedfromtheMilleniumRunsimulation.However,simulatedsubhalosappeartobemoreefficientlystrippedthanlensingobserva-tionssuggest.Thisislikelyanartifactofcomparisonwithadarkmatteronlysimulation.Futuresimulationsthatsimultaneouslyfollowthedetailedevolutionofthebaryoniccomponentduringclusterassemblywillbeneededforamoredetailedcomparison.Subjectheadings:cosmologicalparameters—gravitationallensing—clusters1.IntroductionClustersofgalaxiesarethemostmassiveandrecentlyassembledstructuresintheUni-verse.InthecontextofthehierarchicalgrowthofstructureinacolddarkmatterdominatedUniverse,clustersaretherepositoryofcopiousamountsofthedarkmatter.Gravitationallensing,predictedbyEinstein’stheoryofGeneralRelativity,isthedeflectionoflightraysfromdistantsourcesbyforegroundmassstructures.Initsmostdramaticmanifestation,stronglensingrequiresararealignmentwithforegrounddensestructuresandproduceshighlydistorted,magnifiedandmultipleimagesofasinglebackgroundsource(Schneider,Ehlers&Falco1992).Morecommonly,theobservedshapesofbackgroundsourcesviewedviaaforegroundclusterlensaresystematicallyelongated,intheso-calledweaklensingregime.Strongandweaklensingofferthemostreliableprobesofthedistributionofdarkmatteronvariouscosmicscales(Blandford&Narayan1992;Mellier2002;Schneider,Ehlers&Falco1992).Stronglensingstudiesofthecoreregionsofseveralclustersindicatethatthedarkmatterdistributioncanberepresentedbyacombinationofsmoothlydistributed,extendedclustermasscomponentsandsmaller-scaleclumpsorsubhalosassociatedwithluminousgalaxies(Kneibetal.1996;Natarajan&Kneib1997;Natarajan,Kneib,Smail&Ellis1998).Thesmoothcomponentshavebeendetectedusingweaklensingtechniquesouttotheturn-aroundradius(typicallyoftheorderofseveralMpc)inclusters(Kneibetal.2003;Gavazzietal.2003;Broadhurstetal.2005;Bradacetal.2006;Cloweetal.2006;Wittmanetal.2006;Limousinetal.2007c;Bardeauetal.2007).Todate,however,attentionhaslargelyfocused–3–onthelensingderiveddensityprofileofthesmoothclustercomponent,anditsagreementwithprofilescomputedfromhighresolutionnumericalsimulationsofstructureformationintheUniverse(Navarro,Frenk&White1997;Navarroetal.2004;Sandetal.2004).Infact,thegranularityofthedarkmatterdistributionassociatedwithindividualgalacticsubhalosholdsimportantcluestothegrowthandassemblyofclusters.SeveralearlierstudieshaveexploredthisissuefortheparticularcaseofCl0024+16(Tyson,Kochanski&dell’Antonio1998;Broadhurst,Huang,Frye&Ellis2000;Jeeetal.2007;Smailetal.1996).Thedetailedmassdistributionofclustersandinparticular,thefract