Recent X-ray Observations of Disk Galaxies Tracing the Dynamic Interstellar Medium

I review recent results from our deep ROSAT and Chandra observations of two galaxies, M101 and NGC 4631, in fields of exceptionally low Galactic extinction. Large amounts of X-ray-emitting gas are detected in these galaxies. Such gas is produced primarily

RecentX-rayObservationsofDiskGalaxies:TracingtheDynamicInterstellar

Medium

Q.DanielWang

UniversityofMassachusetts,Amherst

arXiv:astro-ph/0008303v1 18 Aug 2000ABSTRACTIreviewrecentresultsfromourdeepROSATandChandraobservationsoftwogalaxies,M101andNGC4631,in eldsofexceptionallylowGalacticextinction.LargeamountsofX-ray-emittinggasaredetectedinthesegalaxies.Suchgasisproducedprimarilyinmassivestarformingregionsandhaveanaveragecharacteristictemperatureofafewtimes106K.Coolergas(～106K)isfoundtypicallyoutsidegalacticdisksandmayrepresentout owsfromblown-outsuperbubbles.Propagationofstarformation,drivenbytheexpansionofhotgas,appearstobeoperatingingiantHIIcomplexes.Asubstantialfractionofphoto-evaporatedgasinsuchcomplexesmaybemass-loadedintohotgas,whichexplainstheirlargeX-rayluminosities.Theseprocesseslikelyplayanimportantroleindeterminingtheglobalpropertiesoftheinterstellarmedium,especiallythedisk/halointeraction.1.IntroductionX-rayobservationsofnearbydiskgalaxiesareimportanttotheunderstandingofthehotinterstellarmedium(ISM)anditsroleingalaxyevolution.Weareconductinganextensivestudyoftheface-onspiralgalaxyM101basedpartlyonanultra-deep(230ks)ROSATHRIimage,andwehavealsoobtainedaChandraobservationontheedge-ongalaxyNGC4631.Theseobservations,

togetherwithdatainotherwavelengthbands,provideuswithcomplementaryperspectivesofhotgasanditsinteractionwithothergalacticcomponentsinlate-typediskgalaxies.

2.M101

Thisface-ongalaxyallowsustostudytheproductionofhotgasnotonlyundernormalcircumstancesbutalsounderlocalizedstarburstconditions.Di use～0.25keVemissionispresentinthecentral(R 10kpc)regionofthegalaxy(Snowden&Pietsch1995).EnhancedX-rayemissionisalsodetectedinseveralgiantHIIcomplexes(GHCs;Williams&Chu1995).Wangetal.(1999)havereportedtheresultsondiscreteX-raysourcesdetectedintheM101 eld.ButsomeofthesesourcesapparentlyrepresentpeaksofextendedX-ray-emittingfeatures.

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