The Starburst-Interstellar Medium Interaction of NGC 1569 I.(5)

parisonswithOtherGalaxies

ItisusefultocomparetheestimatednumbersofWRstarsinNGC1569withthoseforsimilargalaxiesasafunctionofgalaxypropertiessuchasluminosity,totalmass(dynamical),andionizedgasmass.ThiswedoinFigures7-9.Thedatausedintheproductionofthese gurescamefromseveralsources.ReferenceswhereweobtainedthenumberofWRstarsinthevariousgalaxieswerethefollowing:Masseyetal.(1992);Vacca&Conti(1992);vanderHucht(1996);Izotovetal.(1997);Massey&Johnson(1998b);Bransfordetal.(1999);Breysacher,Azzopardi,&Testor(1999);Drissenetal.

We present the detection of He II sources in the Im galaxy NGC 1569 from HST WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The

(1999);vanderHucht(1999);Gusevaetal.(2000).Absolutemagnitudeswerereadilyavailableinseveralpapers(deVaucouleurs&Pence1978;Thuan&Martin1981;Bergvall&Olofsson1986;Thronsonetal.1990;Kobulnickyetal.1995;Gusevaetal.2000)andtheNASA/IPACExtragalacticDatabase.However,limiteddatacouldonlybefoundonthetotal(dynamical)masses(deVaucouleurs1960;Burns&Roberts1971;Cottrell1976;Loiseau&Bajaja1981;Thuan&Martin1981;Jacksonetal.1987;Dufour&Hester1990;Tayloretal.1993;Kobulnickyetal.1995;Stil&Israel1998;Wilkinson&Evans1999)andionizedhydrogenmasses(Viallefond&Goss1986;Dufour&Hester1990;Sivanetal.1990;Thronsonetal.1990;vandenBroeketal.1991;Waller1991;Vacca&Conti1992;Walterbros&Braun1994;Kennicuttetal.1995;Mendezetal.1999;Gusevaetal.2000).Sincetherearesomanysourcesanddi erentcombinationsofdatafortheordinateandabscissavalues,wehavenotlabeledthevariousdatapointswithdi erentsymbols.Becausewehavetwovalues(detectedandestimatedtotal)ofthenumberofWRstarsinNGC1569,wehaveplottedbothinFigures7-9.Theenlarged,solidNGC1569datumpointisthedetectednumberofWRstars,andtheenlarged,hollowNGC1569datumpointistheestimatedtotalnumberofWRstars.

Figure7plotsthenumberofWRstarsdetectedversustheabsoluteblue(orphotographic)magnitudesofWolf-Rayet,starburst,andspiralgalaxies.TheordinateerrorbarsontheNGC1569datapointsindicateourestimateoftheuncertaintyduetocomplicationsofthenebularHeiidetectedinthegalaxyandtheestimationprocedureforthetotalnumberofWRstarsasexplainedintheprevioussection.TheordinateerrorbarsforamajorityofthepointscomesfromusingtheGusevaetal.(2000)databecausethey ndthenumberofWNLstarswithvariousemissionlines.NGC2403’sordinateerrorbarsarebecauseDrissenetal.(1999)report25-40individualWRstars.Theabscissaerrorbarsofamajorityofthepointscomefromusingtheabsolutephotographicmagnitude(Mpg)fromGusevaetal.(2000).WeareassumingthattheirMpgis±1ofMB.Fromthe