Using Weak Lensing Dilution to Improve Measurement

arXiv:astro-ph/0608499v28Feb2007DRAFTVERSIONFEBRUARY5,2008PreprinttypesetusingLATEXstyleemulateapjv.10/09/06USINGWEAKLENSINGDILUTIONTOIMPROVEMEASUREMENTSOFTHELUMINOUSANDDARKMATTERINA1689ELINORMEDEZINSKI1,TOMBROADHURST1,KEIICHIUMETSU2,DANCOE3,4,NARCISOBENÍTEZ4,HOLLANDFORD3,YOELREPHAELI1,NOBUOARIMOTO5,XUKONG6DraftversionFebruary5,2008ABSTRACTTheE/SOsequenceofaclusterdefinesaboundaryredwardofwhichareliableweaklensingsignalcanbeobtainedfrombackgroundgalaxies,uncontaminatedbyclustermembers.Forbluercolors,bothbackgroundandclustergalaxiesarepresent,reducingtheaveragedistortionsignalbytheproportionofunlensedclustermembers.IndeepSubaruandHST/ACSimagesofA1689,weshowthatthetangentialdistortionofgalaxieswithbluercolorsfallsrapidlytowardtheclustercenterrelativetothebackgroundreferencelevelprovidedbytheredbackground.Weusethisdilutioneffecttoderivetheclusterlightprofileandluminosityfunctiontolargeradius,withtheadvantagethatnosubtractionoffar-fieldbackgroundcountsisrequired.ThelightprofileofA1689isfoundtodeclinesteadilytothelimitofthedata,r2h-1Mpc,withaconstantslope,dlog(L)/dlog(r)=-1.12±0.06,unlikethelensingmassprofilewhichsteepenscontinuouslywithradius,sothatM/Lpeaksatanintermediateradius,≃100h-1kpc.Aflatterbehaviourisfoundforthemorephysicallymeaningfulratioofdark-mattertostellar-matter,whenaccountismadeofthecolor-massrelationofclustermembers.Wederiveaclusterluminosityfunctionwithaflatfaint-endslopeofα=-1.05±0.07,nearlyindependentofradiusandwithnofaintupturntoMi′-12.Weestablishthattheverybluestobjectsarenegligiblycontaminatedbythecluster([V-i′]AB0.2),becausetheirdistortionprofilerisescontinuouslytowardsthecenterfollowingtheredbackground([V-i′]AB1.2),butisoffsethigherby≃20%.Thislargeramplitudeisconsistentwiththegreaterestimateddepthofthefaintbluegalaxieshzi∼2comparedtohzi∼0.85fortheredbackground,apurelygeometriceffect.Withalargersampleofbackgroundgalaxiesbehindseveralclusterswemayusethisgeometriceffecttoconstrainthecosmologicalparametersinamodelindependentway,bycomparingtheweaklensingstrengthoverawiderangeofphotometricallyderivedredshifts.Finally,weimproveuponourearliermodelingofthemassprofilebycombiningboththeredandbluebackgroundpopulations,andveryclearlyexcludelowconcentrationprofilespredictedformassiveCDMdominatedhaloes.Subjectheadings:cosmology:observations–gravitationallensing–galaxies:clusters:individual(Abell1689)–galaxies:luminosityfunction1.INTRODUCTIONTheinfluenceof“Darkmatter”isstrikinglyevidentinthecentersofmassivegalaxyclusters,wherelargevelocitydis-persionsaremeasuredandgiantarcsareoftenvisible.Clustermassesmaybeestimatedbyseveralmeans,leadingtoex-ceptionallyhighcentralmass-to-lightratios,M/LR∼100-300h(M/LR)⊙(Carlbergetal.2001),farexceedingboththemassofstarscomprisingthelightoftheclustergalaxiesandthemassofplasmaderivedfromX-rayemissionandtheSZeffect.Reasonableconsistencyisclaimedbetweendynam-ical,hydrodynamicalandlensing-basedestimatesofclustermasses,supportingtheconventionalunderstandingofgravity.However,thehighmass-to-lightratiorequiresthatanuncon-ventionalnon-baryonicdarkmaterialdominatesthemassofclusters,whoseoriginremainsveryunclear.Indetail,discrepanciesareoftenreportedbetweenmassesderivedfromstronglensingandX-raymeasurements,withtheclaimedX-raymassesoftenlowerinthecentersofclus-ters.HighresolutionX-rayemissionandtemperaturemaps1SchoolofPhysicsandAstronomy,TelAvivUniversity,Israel2InstituteofAstronomyandAstrophysics,AcademiaSinica,P.O.Box23-141,Taipei106,Taiwan,RepucblicofChina3PhysicsandAstronomyDept,JohnsHopkinsUniversity,BaltimoreMaryland,USA4InstitutodeAstrofísicadeAndalucía(CSIC),Granada,Spain5NationalAstronomicalObservatoryofJapan,Mitaka181-8588,Japan6CenterforAstrophysics,UniversityofScienceandTechnologyofChina,Hefei,230026,Anhui,PRChinarevealthatthemajorityoflocalclustersundergorepeatedmergingwithsub-clumps,andobviousshockfrontsareseeninsomecases(Markevitchetal.2002;Reiprichetal.2004).Thedoublecluster1E0657–56(a.k.a.,the“bullet”cluster,z=0.296)isthemostextremeexamplestudied,wheretheassociatedgasformsaflattenedluminousshock-heatedstruc-turelyingbetweenthetwolargedistinctclusters,clearlyin-dicatingthesetwobodiescollidedrecentlyatahighrelativevelocity(Markevitchetal.2004),withthegasremaininginbetweenwhiletheclustergalaxieshavepassedthrougheachotherrelativelycollisionlessly.Veryinterestingly,theweaklensingsignalfollowsthedoublestructureoftheclusters,ratherthanthegasinbetween,cleanlydemonstratingthatthebulkofthematteriscollisionlessanddark(Cloweetal.2004).Thissystemfavorsthestandardcolddarkmatter(CDM)scenario,placesarestrictivelimitontheinteractioncross-sectionofanyfermionicdarkmatter,anddisfavorsaclassofalternativegravitytheoriesinwhichonlybaryonsarepresent(Cloweetal.2004).Smallerbutsignificantdiscrep-anciesofthesamesortarealsoclaimedforotherinteractingclusters(Natarajanetal.2002;Jeeetal.2005).Manyclustersshownoapparentsignsofsignificantongo-inginteraction;thesehavecentrallysymmetricX-rayemis-sionandlittleobvioussubstructure(Allen1998),andforsomeofthesethelensingandX-ray(ordynamical)derivedmassesareclaimedt