Probing The Multiphase Interstellar Medium Of The Dwarf Starburst Galaxy NGC 625 With FUSE

We present new FUSE spectroscopy of the dwarf starburst galaxy NGC 625. These observations probe multiple phases of the interstellar medium, including the coronal, ionized, neutral and molecular gas. This nearby (D = 3.9 +/- 0.2 Mpc) system shows a clear d

observations.Wedetectmultiplelinesofdi useH2absorptionfromtheISMof

NGC625;thisisoneofonlyafewextragalacticsystemswithFUSEdetections

ofH2linesintheLymanandWernerbands.We ndapotentialabundance

o setbetweentheneutralandnebulargasthatexceedstheerrorsonthederived

columndensities.Sincesuchano sethasbeenfoundinmultipledwarfgalaxies,

wediscusstheimplicationsofalower-metallicityhalosurroundingthecentralstar

formingregionsofdwarfgalaxies.Theapparento setmaybeduetosaturation

oftheobservedOiline,andhigherS/Nobservationsarerequiredtoresolvethis

issue.

Subjectheadings:galaxies:starburst—galaxies:dwarf—galaxies:abundances

—galaxies:kinematicsanddynamics—galaxies:individual(NGC625)

1.Introduction

Localstarburstingdwarfgalaxieso erauniqueopportunitytostudythevariousphases

oftheinterstellarmedium(ISM)underextremeconditionsandinunprecedenteddetail.Furthermore,thephysicalconditionsinthesetargetsarelikelyverysimilartothosefoundingalaxiesathighredshifts,makingthemcrucialbenchmarksagainstwhichobservationsofsuchtargetsmustbecompared.Withtheseobservations,wecapitalizeonthehigh-resolutioncapabilitiesoftheFarUltravioletSpectroscopicExplorer(FUSE;seeMoosetal.2000)toobservetheinteractionofthemultiplephasesoftheISMinNGC625,anearby(D=3.9±0.2Mpc;Cannonetal.2003),lowmass(MHI=1.1×108M⊙;Cannonetal.2004),lowmetallicity(12+log(O/H)=8.14±0.02;Skillmanetal.2003b)dwarfirregulargalaxyintheSculptorGroupthatiscurrentlyundergoingamassivestarformationepisode(seeTable1forbasicgalaxyproperties).

Ofparamountimportanceintheevolutionofdwarfgalaxiesistheroleplayedbyout-

owspoweredbytheenergyinputsofsupernovaeandstellarwinds.Theseout owsmaydrivesigni cantfractionsofthegasfromgalaxieswithshallowpotentialwells.Recentsimu-lationssuggestthatthereturnofmetalsintotheintergalacticmedium(IGM) ndsitsmoste ectiveavenueintheselowmassgalaxies(MacLow&Ferrara1999).Understandingthenatureoftheseout owsisthereforeafundamentalastrophysicalproblemwithfar-reachingimplications.TheseFUSEspectraisolatethepowerfuldiagnosticabsorptionlinesofOVI

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