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用WISE数据估算星系的恒星质量和恒星形成率.docx

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用WISE数据估算星系的恒星质量和恒星形成率 Introduction UnderstandingthepropertiesofgalaxiesisfundamentaltoourunderstandingoftheUniverse.Onesuchpropertyisthestarformationrate(SFR),whichtellsushowmanystarsarebeingformedinagalaxyperunittime.Anotherpropertyisthestellarmassofagalaxy,whichtellsusthetotalmassofallthestarsinthegalaxy.Measuringthesepropertiesofgalaxiesisessentialtoseehowtheyarerelatedandhowtheyareaffectedbydifferentphysicalprocesses. Inthispaper,wewillusedatafromtheWide-fieldInfraredSurveyExplorer(WISE)toestimatethestellarmassandSFRofgalaxies.WISEisaspace-basedtelescopethathassurveyedtheentireskyinfourmid-infraredbands,anditprovidesawealthofinformationaboutgalaxiessuchastheirinfraredemissionfromstarformation. Methodology WefirstselectedasampleofgalaxiesfromtheWISEAll-SkyDataRelease.Wechosegalaxieswitharedshiftoflessthan0.1toensurethatwewerenotaffectedbyanycosmologicaleffects,whichwouldmakeourestimatesinaccurate.Wealsodiscardedgalaxiesthathadadetectionlevelbelowourchosenthreshold,whichwassettoasignal-to-noiseratio(SNR)of5inallfourWISEbands. Toestimatethestellarmassofeachgalaxy,weusedarelationbetweentheinfraredfluxdensityandthestellarmassderivedfrompreviousstudies.Thisrelationisbasedontheideathatthemid-infraredemissionfromagalaxyisprimarilyproducedbythedustthatisheatedbystarformation.Thisdustisinequilibriumwiththestellarradiationfield,sothetotalinfraredemissioncanbeusedtoestimatethetotalstellarmassinagalaxy. ToestimatetheSFRofeachgalaxy,weusedarelationbetweentheinfraredfluxdensityandtheSFRderivedfrompreviousstudies.Thisrelationisalsobasedontheideathatthemid-infraredemissioncomesfromdustthatisheatedbystarformation.Thisdustabsorbstheultravioletradiationfromhigh-massstarsandre-emitsitinthemid-infrared,sothemid-infraredfluxdensitycanbeusedtoestimatetheSFR. Results Figure1showsthedistributionofstellarmassesforthegalaxiesinoursample.Themajorityofgalaxieshaveastellarmassoflessthan10billionsolarmasses,withapeakataround1billionsolarmasses.Therearealsoahandfulofgalaxieswithveryhighstellar