Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45

Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45

Astronomy&Astrophysicsmanuscriptno.MMORA˙NGC45˙GC˙FINALAugust6,2008

cESO2008

Spectroscopyofglobularclustersinthelow-luminosityspiral

galaxyNGC45

M.D.Mora1,3,S.S.Larsen2,andM.Kissler-Patig3

arXiv:0808.0922v1 [astro-ph] 6 Aug 2008

1

2

3

DepartamentodeF´ sicayAstronom´ a,FacultaddeCiencias,UniversidaddeValpara´ so.Av.GranBreta na1111,Valpara´ so,Chile.e-mail:mmora@dfa.uv.cl

AstronomicalInstitute,UniversityofUtrecht,Princetonplein5,NL-3584CC,Utrecht,TheNetherlands.e-mail:S.S.Larsen@uu.nl

EuropeanSouthernObservatory,Karl-Schwarzschild-Strasse2,85748GarchingbeiM¨unchen,Germany.e-mail:mkissler@eso.org

Received/Accepted

ABSTRACT

Context.Extragalacticglobularclustershavebeenstudiedinellipticalgalaxiesandinafewluminousspiralgalaxies,butlittleisknownaboutglobularclustersinlow-luminosityspirals.

Aims.PastobservationswiththeACShaveshownthatNGC45hostsalargepopulationofglobularclusters(19),aswellasseveralyoungstarclusters.Inthisworkweaimtocon rmthebona deglobularclusterstatusfor8of19globularclustercandidatesandtoderivemetallicities,ages,andvelocities.

Methods.VLT/FORS2multislitspectroscopyincombinationwiththeLick/IDSsystemwasusedtoderivevelocitiesandtoconstrainmetallicitiesand[α/Fe]elementratiooftheglobularclusters.

Results.Wecon rmthe8globularclustersasbona deglobularclusters.Theirvelocitiesindicatehaloorbulge-likekinematics,withlittleornooverallrotation.FromabsorptionindicessuchasHβ,Hγ,andHδandthecombined[MgFe]′index,wefoundthattheglobularclustersaremetal-poor[Z/H]≤-0.33dexand[α/Fe]≤0.0elementratio.Theseresultsargueinfavorofapopulationofglobularclustersformedduringtheassemblingofthegalaxy.

Keywords.galaxies:individual:NGC45-galaxies:starclusters

1.Introduction

Globularclustersarepresentinalmostallkindsofgalaxies.Observationsofextragalacticglobularclustersystemshaveshownthatglobularclustersystemscanoftenbedividedinto(atleast)twosub-populations,althoughtheoriginofthesere-mainsunclear.IntheMilkyWayandM31,themetal-poorglob-ularclustersub-populationsdisplayhalo-likekinematicsandspatialdistributions(e.g.Zinn1985;Ashman&Zepf1998;Barmbyetal.2000;Perrettetal.2002),whilethemetal-richglobularclustersmaybeassociatedwiththebulgeand/orthickdisk(e.g.Minniti1995;Barbuyetal.1998;C ot´e1999;Bicaetal.2006).Theglobularclustersub-populationsinellip-ticalgalaxiesshowmanysimilaritiestothoseinspirals,andsomeofthemetal-richclustersmayhaveformedingalaxymergers(e.g.Ashman&Zepf1992).Someofthe

metal-poor

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