The polar ring galaxy AM1934-563 revisited

We report long-slit spectroscopic observations of the dust-lane polar-ring galaxy AM1934-563 obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. The observations target the spectral region of the Ha, [NII] a

Mon.Not.R.Astron.Soc.000,(2007)Printed1February2008

A(MNLTEXstyle lev2.2)

ThepolarringgalaxyAM1934-563revisited

arXiv:0706.2150v1 [astro-ph] 14 Jun 2007

NoahBrosch,1,2 AlexeiY.Kniazev,2,3DavidBuckley,2DarraghO’Donoghue,2

YasHashimoto,2NicolaLoaring,2EncarniRomero,2MartinStill,2PetriVaisanen,2EricB.Burgh,4KennethNordsieck4

WiseObservatoryandtheSchoolofPhysicsandAstronomy,theRaymondandBeverlySacklerFacultyofExactSciences,TelAvivUniversity,TelAviv69978,Israel

2SouthAfricanAstronomicalObservatory,ObservatoryRoad,CapeTown,SouthAfrica3SpecialAstrophysicalObservatory,NizhnijArkhyz,Karachai-Circassia,369167,Russia4SpaceAstronomyLaboratory,UniversityofWisconsin,Madison,WI53706,USA

1The

Accepted2007April??.Received2007March??;inoriginalform2007March??

ABSTRACT

Wereportlong-slitspectroscopicobservationsofthedust-lanepolar-ringgalaxyAM1934-563obtainedwiththeSouthernAfricanLargeTelescope(SALT)duringitsperformance-veri cationphase.TheobservationstargetthespectralregionoftheHα,[Nii]and[Sii]emission-lines,butshowalsodeepNaIstellarabsorptionlinesthatweinterpretasproducedbystarsinthegalaxy.Wederiverotationcurvesalongthemajoraxisofthegalaxythatextendouttoabout8kpcfromthecenterforboththegaseousandthestellarcomponents,usingtheemissionandabsorptionlines.Wederivesimilarrotationcurvesalongthemajoraxisofthepolarringandpointoutdi erencesbetweentheseandtheonesofthemaingalaxy.

Weidentifyasmalldi useobjectvisibleonlyinHαemissionandwithalowvelocitydispersionasadwarfHiigalaxyandarguethatitisprobablymetal-poor.ItsvelocityindicatesthatitisafourthmemberofthegalaxygroupinwhichAM1934-563belongs.

Wediscusstheobservationsinthecontextoftheproposalthattheobjectistheresultofamajormergerandpointoutsomeobservationaldiscrepanciesfromthisex-planation.Wearguethatanalternativescenariothatcouldbetter ttheobservationsmaybetheslowaccretionofcoldintergalacticgas,focusedbyadense lamentofgalaxiesinwhichthisobjectisembedded.

Giventhepatternofrotationwefound,withtheasymptoticrotationofthegasintheringbeingslowerthanthatinthediskwhilebothcomponentshaveapproximatelythesameextent,wepointoutthatAM1934-563maybeagalaxyinwhichadarkmatterhalois attenedalongthegalacticdiskandthe rstobjectinwhichthispredictedbehaviourofpolarringgalaxiesindarkmatterhaloesisful lled.

Keywords:galaxies:ringgalaxies—galaxies:evolution—galaxies:individual:AM1934-563—galaxies:darkmatter—galaxies:galaxyhaloes

INTRODUCTION

Ringgalaxiesposedsigni cantastronomicalinterestsinceLynds&Toomre(1976)modelledtheCartwheelgalaxyastheresultofasmallgalaxypassingthroughalargerone.

BasedonobservationsobtainedwiththeSouthernAfricanLargeTelescope(SALT).

E-mail:noah@wise.tau.ac.il(NB);akniazev@saao.ac.za(AYK);dibnob@saao.ac.za(DB);dod@saao.ac.za(DOD);hashimot@saao.ac.za(YH);nsl@saao.ac.za(NL);erc@saao.ac.za(ER);still@saao.ac.za(MS);petri@saao.ac.za(PV);ebb@sal.wisc.edu(EBB);khn@sal.wisc.edu(KN)

Whilesucheventsprobablyhappenandproducesomeoftheringgalaxies,inotherinstancesdi erentmechanismsmightbeatwork.Aparticularlyinterestingkindofringgalaxyisthepolarringgalaxy(PRG)wherea atteneddiskgalaxyexhibitsanouterringofstarsandinterstellarmatterthatrotateinaplaneapproximatelyperpendiculartothecentraldisk.AnextensivecatalogofPRGswasproducedbyWhitmoreetal.(1990).

TheissueofPRGswasreviewedbyCombes(2006).ShereviewedanumberofformationmechanismsforPRGs:minorormajormergers,tidalaccretionevents,ordirectcoldgasaccretionfrom lamentsofthecosmicweb.

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