Interacting and Merging Galaxies

Interacting and Merging Galaxies

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aInteractingandMergingGalaxiesUtaFritze-vonAlvenslebenUniversit¨atssternwarteG¨ottingen,Geismarlandstraße11,37083G¨ottingen,GermanyAbstract.Iwillpresentareviewofsomeofthemanyrecentdevelop-mentswithintheexcitingandrapidlyevolving eldofInteractingandMergingGalaxies.Iwilltouchbothonobservationsandontheory,fo-cussingonthoseaspectswheregalaxyevolutionmodellingmaypossiblycontributetoourunderstanding.Afterbrie youtliningthebasicconceptsandafewspeci cresultsofstellar-andgasdynamicalmodellingofgalaxy–galaxymergers(Sect.1)Ichoosethreeexamplesofinteracting/mergedgalaxypairstodiscussdi erentaspectsofmergers:tracingbackthestarformationhistoryoftheoldmergerremnantNGC7252(Sect.2),theformationofyoungstarclusters(Sect.3)anddwarfgalaxies(Sect.4)in“TheAntennae”,andthemoleculargascontentofIR-ULgalaxiesontheexampleofArp220(Sect.5).I’lltouchtheinteraction–activityconnectioninSect.6andreportattemptstoidentifymergerremnantsamongtoday’sgalaxiesinSect.7.Afterfewwordsonmergerratesatpresentandinthepast(Sect.8),I’llclosewithabriefoutlook.1.Howitallbegan...Arp’sAtlasofPeculiarGalaxies(1966)showsanimpressivevarietyofdisturbedgalaxies,manyofwhichareevidentlyinteractingormerging.TheseminalworkofToomre&Toomre(1972)putforwardawholebunchofideaswhichkeep

stimulatingresearchsincemorethan20years.TheirbasicideawasthattheHubblesequenceofgalaxiesneednotbegivenabinitioadin nitum,i.e.thatHubbletypesmaychangeinthecourseofstronginteractions.Witharestricted3-bodyalgorithmforanN～120 bodysystemofparticlestheymodelledthemergingoftwospiralsandshowedthattheremnantmaylookverymuchlikeanelliptical.Comparingtheirmodelstonearbyexamplesofapparentlyinter-acting/merginggalaxies–mostfromArp’satlas–theyestablishedtheirfamousagesequenceoftheeleven.TheearlieststageofinteractionisrepresentedbyArp244=NGC4038/39=“TheAntennae”andthelateststageofacompletedmergerbyArp226=NGC7252,bothofwhichI’llpresentinsomedetailinSect.2&3.EstimatingthegalaxymergerrateamongNGCgalaxiestheyfoundthenumberofgalaxiesthatshouldhaveexperiencedamajormergeroveraHubbletimetobecomparabletothenumberofE/S0galaxies,thusraisingthesuspicionthatsomeorevenallE/S0galaxiesmightbeproducedbySp–Spmergers.Furthermore,theyalreadyconsideredapossibleinteraction–activity

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