Massive Dark-matter halos and Evolution of Early-t

arXiv:astro-ph/0401373v21May2004ApJ,inpressPreprinttypesetusingLATEXstyleemulateapjv.11/12/01MASSIVEDARK-MATTERHALOSANDEVOLUTIONOFEARLY–TYPEGALAXIESTOZ≈1TommasoTreu2,3,5&L´eonV.E.Koopmans4,6,7ApJ,inpressABSTRACTThecombinationofgravitationallensingandstellardynamicsbreaksthemass-anisotropydegeneracyandprovidesstringentconstraintsonthedistributionofluminousanddarkmatterinearly-type(E/S0)galaxiesouttoz≈1.Wepresentnewobservationsandmodelsofthreelenssystems(CFRS03.1077,HST14176+5226,HST15433+5352)andthecombinedresultsfromthefivefieldE/S0lensgalaxiesatz≈0.5−1.0analyzedaspartoftheLensesStructure&Dynamics(LSD)Survey.Ourmainresultsare:(i)Constantmass-to-lightratiomodelsareruledoutat99%CLforallfiveE/S0galaxies,consistentwiththepresenceofmassiveandextendeddark-matterhalos.Therangeofprojecteddark-mattermassfractionsinsidetheEinsteinradiusisfDM=0.37–0.72,or0.15–0.65insidetheeffectiveradiusReforisotropicmodels.(ii)Theaverageeffectivepower-lawslopeofthetotal(luminous+dark;ρtot∝r−γ′)massdistributionishγ′i=1.75±0.10(1.57±0.16)forOsipkov-Merrittmodelswithanisotropyradiusri=∞(Re)withanrmsscatterof0.2(0.35),i.e.marginallyflatterthanisothermal(γ′=2).Theratiobetweentheobservedcentralstellarvelocitydispersionandthatfromthebest-fitsingularisothermalellipsoid(SIE)lensmodelishfSIEi=hσ/σSIEi=0.87±0.04with0.08rms,consistentwithflatter-than-isothermaldensityprofiles.Consideringthatγ′2andfSIE1havebeenreportedforothersystems(i.e.B1608+656andPG1115+080),weconcludethatthereisasignificantintrinsicscatterintheslopeofthemass-densityprofileoflensgalaxies(rms∼15%),similartowhatisfoundforlocalE/S0galaxies.Hence,theisothermalapproximationisnotsufficientlyaccurateforapplicationsthatdependcriticallyontheslopeofthemass-densityprofile,suchasthemeasurementoftheHubbleConstantfromtime-delays.(iii)Theaverageinnerpower-lawslopeγofthedark-matterhaloisconstrainedtobehγi=1.3+0.2−0.4(68%C.L.),ifthestellarvelocityellipsoidisisotropic(ri=∞)oranupperlimitofγ0.6,ifthegalaxiesareradiallyanisotropic(ri=Re).Theobservedrangeofslopesoftheinnerdark-matterdistributionisconsistentwiththeresultsfromnumericalsimulationsonlyforanisotropicvelocityellipsoidandifbaryoniccollapseandstar-formationdonotsteependark-matterdensityprofiles.(iv)Theaveragestellarmass-to-lightratioevolvesasdlog(M∗/LB)/dz=−0.72±0.10,obtainedviaaFundamentalPlaneanalysis.Anindependentanalysisbasedonlensinganddynamicsgivesanaveragehdlog(M∗/LB)/dzi=−0.75±0.17.Bothvaluesindicatethatthemass-to-lightratioevolutionforoursampleoffieldE/S0galaxiesisslighlyfasterthanthoseinclusters,consistentwiththehypothesisthatfieldE/S0galaxiesexperiencesecondarybursts(∼10%inmass)ofstarformationatz1.ThesefindingsareconsistentwithpureluminosityevolutionofE/S0galaxiesinthepast8Gyrs,andwouldbehardtoreconcilewithscenariosinvolvingsignificantstructuralanddynamicalevolution.Subjectheadings:gravitationallensing—galaxies:ellipticalandlenticular,cD—galaxies:evolution—galaxies:formation—galaxies:structure1.introductionAcentralassumptionofthecurrentstandardΛCDMcosmologicalmodelisthatgalaxiesformandevolveinsidedark-matterhalos(White&Rees1978;Blumenthaletal.1984;Davisetal.1985).Darkmatterhalosareubiquitousandpossiblyuniversalintheirdensityprofile(Navarro,Frenk&White1996,1997,hereafterNFW;Mooreetal.1998)andtheydominatethedynamicsoflargescalestruc-tures.Inspiteofdecadesofsearchesandtechnologicaladvancesourempiricalknowledgeofdarkhalosremainsverysparse.InthelocalUniverse,dark-matterhaloshavebeencon-vincinglydetected–predominantlythroughdynamicaltracers–inspiralgalaxies(e.g.Rubin,Thonnard,&Ford1978,1980;Faber&Gallagher1979;vanAlbada&Sancisi1986;Salucci&Burkert2000;Jimenez,Verde&Oh2003),dwarfandlowsurfacebrightnessgalaxies(deBlok&Mc-Gaugh1997;vandenBoschetal.2000;Swaters,Madore&Trewella2000),clustersofgalaxies(Zwicky1937;Kneibetal.1993;Lombardietal.2000;Sandetal.2002,2004;Kneibetal.2003),and–atleastinsomecases–inearly-1BasedonobservationscollectedatW.M.KeckObservatory,whichisoperatedjointlybytheCaliforniaInstituteofTechnologyandtheUniversityofCalifornia,andwiththeNASA/ESAHubbleSpaceTelescope,obtainedatSTScI,whichisoperatedbyAURA,underNASAcontractNAS5-26555.2DepartmentofPhysicsandAstronomy,UniversityofCaliforniaatLosAngeles,LosAngeles,CA90095;[e-mail]3HubbleFellow4SpaceTelescopeScienceInstitute,3700SanMartinDr,Baltimore,MD212185CaliforniaInstituteofTechnology,Astronomy,mailcode105–24,Pasadena,CA911256CaliforniaInstituteofTechnology,TheoreticalAstrophysics,mailcode130–33,Pasadena,CA911257CurrentAdress:KapteynAstronomicalInstitute,P.O.Box800,9700AVGroningen,TheNetherlands12Treu&Koopmanstypetypegalaxies(e.g.Fabbiano1989;Mouldetal.1990;Matsushitaetal.1998;Loewenstein&White1999;Saglia,Bertin&Stiavelli1992;Bertinetal.1994;Arnaboldietal.1996;Franxetal.1994;Carolloetal.1995;Rixetal.1997;Gerhardetal.2001;Borriello,Salucci&Danese2003;Seljak2002).However,observationalevidencere-gardingdark-matterhalosofearly-typegalaxies(E/S0s)islimited.Inanumberofcases,constantmass-to-lightmodels,withamass-to-lightratioconsistentwiththoseofanormalstellarpopulation,appearsufficien