Kinematic properties of gas and stars in 20 disc g

arXiv:astro-ph/0105234v114May2001Astronomy&Astrophysicsmanuscriptno.(willbeinsertedbyhandlater)Kinematicpropertiesofgasandstarsin20discgalaxies⋆,⋆⋆J.C.VegaBeltr´an1,2,A.Pizzella3,E.M.Corsini3,J.G.Funes,S.J.4,W.W.Zeilinger5,J.E.Beckman1,andF.Bertola61InstitutoAstrof´ısicodeCanarias,CalleViaLacteas/n,E-38200LaLaguna,Spain2GuestinvestigatoroftheUKAstronomyDataCentre3OsservatorioAstrofisicodiAsiago,DipartimentodiAstronomia,Universit`adiPadova,viadell’Osservatorio8,I-36012Asiago,Italy4VaticanObservatory,UniversityofArizona,Tucson,AZ85721,USA5Institutf¨urAstronomie,Universit¨atWien,T¨urkenschanzstrasse17,A-1180Wien,Austria6DipartimentodiAstronomia,Universit`adiPadova,vicolodell’Osservatorio5,I-35122Padova,ItalyVersion:February1,2008Abstract.Ionizedgasandstellarkinematicalparametershavebeenmeasuredalongthemajoraxisof20nearbydiscgalaxies.Wediscussthepropertiesofeachsamplegalaxydistinguishingbetweenthosecharacterizedbyregularorpeculiarkinematics.Inearly-typediscgalaxiesionizedgastendstorotatefasterthanstarsandtohavealowervelocitydispersion(VgV⋆andσgσ⋆),whereasinlate-typespiralsgasandstarsshowalmostthesamerotationvelocitiesandvelocitydispersions(Vg≃V⋆andσg≃σ⋆).Incorporatingtheearly-typediscgalaxiesstudiedbyBertolaetal.(1995),Fisher(1997)andCorsinietal.(1999),wehavecompiledasampleofsome40galaxiesforwhichthemajor-axisradialprofilesofboththestellarandgaseouscomponentshavebeenmeasured.Thevalueofσ⋆measuredatRe/4turnsouttobestronglycorrelatedwiththegalaxymorphologicaltype,whileσgisnotandsometimestakesvaluesabovetherangeexpectedfromthermalmotionsorsmall-scaleturbulence.Keywords.galaxies:kinematicsanddynamics–galaxies:ellipticalandlenticular,cD–galaxies:spiral1.IntroductionOurcurrentunderstandingofgalaxyformationhasgreatlybenefitedfromtheresultsofN−bodymodellingofstruc-tureformationintheearlyUniverse,whichpredictsthatsmallobjectscombinegravitationallytoproducethegalaxiesweseetoday:aprocesscalledhierarchical-clustering-merging(hereafterHCM,cf.Kauffmannetal.1993).OneofthetenetsoftheHCMparadigmisthatgalaxiesareconstantlymergingwithoneanother.InthecaseofellipticalandS0galaxies,thereisampleobser-vationalevidencethattheyarecontinuallysubjectedtomergerswithsmaller,neighbouringgalaxies(cf.Schweizer1998).Sendoffprintrequeststo:JuanCarlosVegaBeltr´an⋆BasedonobservationscarriedoutattheEuropeanSouthernObservatory,attheMultipleMirrorTelescopeObservatory,attheObservatoriodelRoquedelosMuchachos,attheObservatoriodelTeide,andattheMountGrahamInternationalObservatory.⋆⋆Tables5and6areonlyavailableinelectronicformattheCDSviaanonymousftptocdsarc.u-strasbg.fr(130.79.128.5)orvia:[e-mail]ersal,spiralsaresubjecttothesameformationprocessesasE’sandS0’s.Oftenthefingerprintsofsuchsecondeventsresideinthestellarand/orgaseouskinematicsofagalaxyratherthaninitsmorphology.Thisisparticularlytrueifweconsiderthatthemostevident‘morphologicaltracers’ofinteractionssuchaspeculiarorspindlegalaxiesmakeuplessthan5%ofallobjectsinanyoneoftheRC3(deVaucouleursetal.1991),UGC(Nilson1973)orESO/Upssala(Lauberts1982)galaxycatalogues.Itisthereforecrucialtoobtaindetailedkinematicparametersofbothstarsandgastoun-veiltherelicsofaccretionormergingeventswhichhaveoccurredingalaxyhistory.Alargefractionofspiralsex-hibitkinematicdisturbancesrangingfrommildtoma-jor,andcangenerallybeexplainedasthevisiblesignsoftidalencounters(Rubin,Waterman&Kenney1999).Inrecentyearsanumberofotherwisemorphologicallyundis-turbedspiralshavebeenfoundwhichhostkinematically-decoupledcomponents(KDC’s),suchasstellarKDC’s(Bertolaetal.1999;Sarzietal.2000),counter-rotatingextendedstellardiscs(Merrifield&Kuijken1994;Bertolaetal.1996;Joreetal.1996),counter-rotatingordecou-pledgaseousdiscs(Braunetal.1992;Rubin1994;Rixet2VegaBeltr´anetal.:Kinematicpropertiesofgasandstarsin20discgalaxiesal.1995;Cirietal.1995;Haynesetal.2000;Kannappan&Fabricant2001)andpossiblycounter-rotatingbulges(Pradaetal.1996;butseealsoBottema1999).Studyingtheinterplaybetweenionizedgasandstellarkinematicsallowsustoaddressotherissuesconcerningthedynamicalstructureofspirals.Theseincludetheori-ginofdischeatingandthepresenceofstellarorgaseousdiscsingalacticnuclei.Gravitationalscatteringfromgiantmolecularcloudsandspiraldensitywavesaretheprimecandidatestoexplainthefinitethicknessofstellardiscs.ItisexpectedthatthedominantheatingmechanismvariesalongtheHubblesequencebutuptonowonlytwoexter-nalgalaxieshavebeenstudiedindetail(Gerssen,Kuijken&Merrifield1996,2000).ThepresenceinthenucleiofS0’sandspiralsofsmallstellar(Emsellemetal.1996;Kormendyetal.1996a,b;vandenBosch,Jaffe&vanderMarel1998;Scorza&vandenBosch1998;vandenBosch&Emsellem1998)and/orgaseousdiscs(Rubin,Kenney,&Young1997;Bertolaetal.1998;Funes2000)isusuallyconnectedtothepresenceofacentralmassconcentra-tion.Italsoappearsthatthecentralblack-holemassisverystronglycorrelatedwiththestellarvelocitydisper-sionofthehostgalaxybulgeasrecentlyfoundbydif-ferentauthors(Ferrarese&Merritt2000;Gebhardtetal.2000).Thisrelationishoweverbasedonsampleswhic