Dark matter within high surface brightness spiral

arXiv:astro-ph/0212290v112Dec2002SubmittedtoApJ:;accepted:DarkmatterwithinhighsurfacebrightnessspiralgalaxiesThiloKranz1,3,AdrianneSlyz2andHans-WalterRix1ABSTRACTWepresentresultsfromadetaileddynamicalanalysisoffivehighsurfacebrightness,latetypespiralgalaxiesNGC3810,NGC3893,NGC4254,NGC5676,andNGC6643whichwerestudiedwiththeaimtoquantifytheluminous-to-darkmatterratioinsidetheiropticalradii.Thegalaxies’stellarlightdistri-butionandgaskinematicshavebeenobservedandcomparedtohydrodynamicgassimulationswhichpredictthegasdynamicsarisinginresponsetoempiri-calgravitationalpotentials,whicharecombinationsofdifferingstellardiskanddarkhalocontributions.Thegravitationalpotentialofthestellardiskwasde-rivedfromnear-infraredphotometry,color-correctedtoyieldaconstantstellarmass-to-lightratio(M/L);forthedarkhalo,themassdensitydistributionofanaxisymmetricisothermalspherewithacorewaschosen.Hydrodynamicgassimulationswereperformedforeachgalaxyforasequenceoffivedifferentmassfractionsofthestellardiskandforawiderangeofspiralpatternspeeds.Thesetwoparametersmainlydeterminethemodelledgasdistributionandkinematics.Theagreementbetweenthesimulatedandobservedgaskinematicspermittedustoconcludethatthegalaxieswiththehighestrotationvelocitiestendtopossessverymassivestellardiskswhichdominatethegasdynamicswithintheopticalradius.Inlessmassivegalaxies,withamaximalrotationvelocityof200kms−1,themassofthedarkhaloatleastequalsthestellarmasswithin2–3diskscalelengths.Themaximaldiskstellarmass-to-lightratiointheK-bandwasfoundtolieataboutM/LK≈0.6.Furthermore,thegasdynamicsimulationsprovideapowerfultooltoaccuratelydeterminethedominantspiralpatternspeedforgalaxies,independentofaspecificdensitywavetheory.Itwasfoundthatthe1Max-Planck-Institutf¨urAstronomie,K¨onigstuhl17,69117Heidelberg,Germany;[e-mail],[e-mail]2NuclearandAstrophysicsLaboratory,KebleRoad,OX13RHOxford,UK;[e-mail]3nowat:GermanAerospaceCenterDLR,K¨onigswintererStraße522–524,53227Bonn,Germany;[e-mail]–2–locationofthecorotationresonancefallsintoanarrowrangeofaroundthreeexponentialdiskscalelengthsforallgalaxiesfromthesample.Thecorotationresonanceenclosesthestrongpartofthestellarspiralinallcases.Basedontheexperiencegainedfromthisproject,theuseofacolor-correctiontoaccountforlocalstellarpopulationdifferencesisstronglyencouragedwhenpropertiesofgalacticdisksarestudiedthatrelyontheirstellarmassdistributions.Subjectheadings:galaxies:kinematicsanddynamics—galaxies:structure—galaxies:halos—galaxies:spiral1.INTRODUCTIONMuchevidencehasaccumulatedinrecentyearsthatthestellardisksofhighsurfacebrightnessspiralgalaxiesdominatethemassbudgetoftheinnerregions.Mostofthestudiesarguingforamaximaldiskscenario,arebasedonthedetailedanalysisofhighresolutionrotationcurvemeasurements(Blais-Ouelletteetal.1999;Palunas&Williams2000;Ratnam&Salucci2000;Salucci2001).Thesestudies,however,generallyderivetherotationalsupportofthestellardiskfromanaxisymmetricdiskmassmodelandallownoconsiderationofnon-circularrotationcomponents.Moresophisticatedmodellingstrategieshavebeenappliedtospiralgalaxieswithvariablesignificance(Erickson,Gottesman,&Hunter1999;Pignatellietal.2001).Forthemostpartthosestudiesalsosupportheavydisksforhighsurfacebrightnessgalaxies,buttheyalsofindcandidatesforwhichlowerdiskmassfractionsaremorelikely.Themostconvincingdirectargumentsforthemaximaldiskscenariocomefromthestudiesofstrongbarsinspiralgalaxies.Thesefeaturesinduceastrongdynamictraceinthevelocityfieldandprovideagoodlaboratoryforestimatingthestellarmasscomponent.Basedonfluiddynamicmodelling,amaximaldisksolutionisfoundbyEnglmaier&Gerhard(1999)fortheMilkyWayandbyWeiner,Sellwood,&Williams(2001)forNGC4123.Furthermore,theoreticalconsiderationshintfortherequirementofanon-massivehalocontributioninthecentralregionsofstronglybarredgalaxieswithaverycolddisk,becauseotherwisedynamicalfrictionwouldslowdownthebarveryquickly,leadingtoitsdestructionDebattista&Sellwood(1998,2000).Ontheotherhand,forinitiallyhotterdisks,thiseffectislargelyreducedAthanassoula(2002)andreferencestherein.However,thereisalsoevidencethatevenhighsurfacebrightnessspiralgalaxiesmightbedominatedbythedarkmattermasscomponentintheircentraldiskregionsassuggestedbyhighresolutionsimulationsofcosmologicaldarkmatterhalos(Mooreetal.1999a;Ghignaetal.2000;Fukushige&Makino2001,e.g.).Bottema(1997)inferredfromstellarvelocitydispersionsinspiralgalaxydisksthatamoremassivehalocomponentisneededtoexplain–3–thefindings.Therearerecentstudiesthatargueforlighterdiskmodelsbymakinguseofpreviouslyhardlyexploitedrelations.Courteau&Rix(1999)appliedastatisticalTully-Fisherrelationanalysistoalargesampleofgalaxiestryingtorelatethemaximalrotationvelocityofagalaxytoitsdisksize.Maller,Simard,&Guhathakurta(2000),andmorerecentlyTrott&Webster(2002)usedthegeometryofgravitationallylensedsystemstodisentangletheeffectsofthestellardiskandthehalomasses.Thesegroupsfoundthatthedarkhaloalsodynamicallyplaysanimportantroleinthegalaxies’innerregions.Inthepresentstudy,wequantifytherelativemassfractionsofthestellardiskandtheinnerdarkhalobyanalyzingthe