Internal kinematics and stellar populations of early-type galaxies in the Fornax cluster

INTERNALKINEMATICSANDSTELLARPOPULATIONSOFEARLY-TYPEGALAXIESINTHEFORNAXCLUSTER

BettinaGerken1,2,HaraldKuntschner1,RogerL.Davies21

EuropeanSouthernObservatory,Karl-Schwarzschild-Str.2,85748GarchingnearMunich,Germany2

UniversityofOxford,DepartmentofAstrophysics,DenysWilkinsonBuilding,KebleRoad,OxfordOX13RH,UnitedKingdom

Abstract.Wepresentastudyoftheinternalkinematicsandstellarpopulationsofearly-typegalaxiesintheFornaxclusterbasedonintegral-fieldspectroscopicobservationswithGeminiSouthGMOSandVLT-VIMOS.Sevengalaxiesinaluminosityrangeof-21.3≤MB≤-17.7havebeenobservedwiththeseintegralfieldunits(IFU).Asfirstresults,velocityandlinestrengthmapsarepresentedforNGC1427andNGC1419.

1Introduction

Ellipticalgalaxiesandbulgesdivideintotwogroupswithfundamentaldifferencesintheirmorphological,dy-namicandcoreprofileproperties[1,2].Luminoussystemsrotateslowly,haveboxyisophotesandcores,whereasfaintearly-typegalaxiesshowrapidrotation,discyisophotesandacuspycentralluminosityprofile.Thesedif-ferencescanbeinterpretedasdifferencesintheformationofbothclasseswhichmaybereflectedintheirstellarpopulations.Studiesofstellarpopulationshaverevealedsignsofsecondarystarformationinsomelenticulargalaxies[3].Manyearly-typegalaxiesshowkinematicpeculiaritiessuchasnuclearstellarandgaseousdiscs,kinematicallydecoupledcomponents(KDC)orminoraxisrotation[4].Acombinationof2-dimensionalkine-maticsandstellarpopulationanalysisprovidesinformationabouttheformationhistoryofearly-typegalaxies.

2TheFornaxIFUsurvey

TheFornaxclustergalaxiesNGC1427,NGC1380,NGC1381wereobservedwiththeGMOSIFU,andasecondsampleofNGC1339,NGC1375,NGC1419andESO358-G25andadditionallyNGC3379wereobservedwiththeVIMOSIFU.TheVIMOSIFUhasalargefieldofviewof27′′×27′′ataspatialresolutionof0.67′′,whereasGMOShasasmallerfieldofviewof5′′×7′′butoffersaspatialresolutionof0.14′′.ThisapproachallowsastudyofthelargerkinematicscalesandtodetectpossiblelinestrengthgradientsintheVIMOSsample,whileontheotherhandtheverycentresofthegalaxiesobservedwithGMOScanbestudiedingreatdetail.Relationsbetweentheinternalkinematicsandstellarpopulationsareindicativeofthestarformationhistoryofthehostgalaxy.Thewavelengthrangeofthecombinedsample,approximately4200˚Ato5500˚A,includesHβandhigherorderBalmerlines,allowinganagemeasurementlargelyinsensitivetometallicityeffects.SeveralFeindicesandMglinestrengthsaremeasuredtodeterminethemetallicityand[Mg/Fe]ratioofthestellarpopulations.

Figure2:LinestrengthmapsofNGC1427(toppanels)andNGC1419(bottompanels).TheindicesshownareHβ(left)andMgb(right).Theindexrangesin˚Aandcolourscalesaregiventotherightofthemaps.AllmapsarebinnedtoaminimumS/Nof50.

3Results

Fig.1showsthestellarvelocitymapsofNGC1427(leftpanel)andNGC1419(rightpanel).TheknowndecoupledcoreofNGC1427isclearlyvisible.Forthefirsttime,akinematicallydecoupledcoreisalsodetectedinNGC1419.LinestrengthmapsforthesamegalaxiesareshowninFig.2.ThetoppanelsshowtheHβ(left)andMgb(right)distributioninNGC1427,whilethebottompanelsshowthesameforNGC1419.IntheHβdistribution,thereisanincreasetowardsthecentrevisibleinNGC1419,whereasthedistributionisalmostflatinNGC1427.BothgalaxiesshowanMgbgradientwithincreasinglinestrengthstowardsthecentre,whichismorepronouncedinNGC1419.Acomparisonbetweenthevelocityandlinestrengthmapsimpliesthatthestellarpopulationsinthedecoupledcomponentsdonotdiffersignificantlyfromthemainbodyofthegalaxies.Acknowledgements.WewouldliketothankBryanMillerandtheGeminiSouthstaffforefficientsupportduringtheobservationsandwiththedatareduction.

References

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[4]Emsellem,Cappellari,Peletieretal.2004,MNRAS,352,721