The Nature of the Low-Metallicity ISM in the Dwarf Galaxy NGC 1569

We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to understand the nature of the various dust components in low-metallicity environments, which may be comparable to the ISM of galaxies in their early evolutionary sta

J.Phys.IVFrance1(2008)

cEDPSciences,LesUlis Pr1-1

arXiv:astro-ph/0212441v1 19 Dec 2002TheNatureoftheLow-MetallicityISMintheDwarfGalaxyNGC1569Fr´ed´ericGalliano1,SuzanneMadden1,AnthonyJones2,ChristineWilson3,Jean-PhilippeBernard2andFrancineLePeintre21Serviced’Astrophysique,CEA/Saclay,L’OrmedesMerisiers,91191GifsurYvette,France2Institutd’AstrophysiqueSpatiale(CNRS),UniversitedeParisXI,91405Orsay,France3DepartmentofPhysicsandAstronomy,McMasterUniversity,Hamilton,ONL8S4M1,CanadaAbstractWearemodelingthespectraofdwarfgalaxiesfrominfraredtosubmillimeterwavelengthstounderstandthenatureofthevariousdustcomponentsinlow-metallicityenvironments,whichmaybecomparabletotheISMofgalaxiesintheirearlyevolutionarystate.Theoverallnatureofthedustintheseenvironmentsappearstodi erfromthoseofhighermetallicitystarburstingsystems.Here,wepresentastudyofoneofoursampleofdwarfgalaxies,NGC1569,whichisanearby,well-studiedstarburstingdwarf.UsingISOCAM,IRAS,ISOPHOTandSCUBAdatawiththeD´esertetal(1990)model,we ndconsistencywithlittlecontributionfromPAHsandVerySmallGrainsandarelativeabundanceofbiggercoldergrains,whichdominatetheFIRandsubmillimeterwavelengths.Wearecompelledtouse4dustcomponents,addingaverycolddustcomponent,toreproducethesubmillimetreexcessofourobservations.1INTRODUCTION

DwarfgalaxiesinourlocaluniverseareideallaboratoriesforstudyingtheinterplaybetweentheISMandstarformationinlow-metallicityenvironments(Hunter&Gallagher1989).Theyareatrelativelyearlyepochsoftheirchemicalevolution,possiblyresemblingdistantproto-galaxiesintheirearlystagesofstarformation.Althoughonlyafewmetal-poorgalaxieshavebeenobservedintheMIRusingISO,thecharacteristicsoftheMIRdustcomponentsappeartodi erremarkablyfromthoseofnormal-metallicitystarbursts(Madden2000).Whetherthisisanabundanceorcompositione ectisnotyetclear.

Forthisreason,wearestudyingtheirdetailedluminositybudgetbymodelingtheirspec-tralenergydistributions(SEDs)fromopticaltomillimeterwavelengths,therebyconstructingtemplatestostudyconditionsinprimordialgalaxiestohelptoconstraingalaxyevolutionmodels.

ThegalaxywepresenthereisNGC1569.ItisaHI-rich,metal-poor(Z=0.25Z⊙)dwarfirregulargalaxywhichliesnearthegalacticplaneatadistanceof(2.2±0.6)Mpc(Israel1988).NGC1569ispresentlyintheaftermathofamassiveburstofstarformation(Israel1988,Israel&DeBruyn1988,Waller1991)andexhibitsverycompactHIIregionsand2super-star-clusters(Hunteretal2000).

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