The 21 cm Transition and the High-Redshift Universe

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1、CosmologyatLowFrequencies:The21cmTransitionandtheHigh-RedshiftUniverseStevenR.Furlanettoa,1,S.PengOhb,andFrankH.BriggscaDepartmentofPhysics,YaleUniversity,POBox208121,NewHaven,CT06520,USAbDepartmentofPhysics,UniversityofCalifornia,SantaBarbara,CA93106,USAcRese

2、archSchoolofAstronomyandAstrophysics,TheAustralianNationalUniversity,MountStromloObservatory,CotterRoad,Weston,ACT2611,AustraliaAbstractObservationsofthehigh-redshiftUniversewiththe21cmhyperfinelineofneutralhydrogenpromisetoopenanentirelynewwindowontotheearlyph

3、asesofcosmicstructureformation.Herewereviewthephysicsofthe21cmtransition,focusingonprocessesrelevantathighredshifts,anddescribetheinsightstobegainedfromsuchobservations.Theseincludemeasuringthematterpowerspectrumatz∼50,observingtheformationofthecosmicwebandthe

4、firstluminoussources,andmap-pingthereionizationoftheintergalacticmedium.Theepochofreionizationisofparticularinterest,becauselargeHIIregionswillseedsubstantialfluctuationsinthe21cmbackground.Wealsodiscusstheexperimentalchallengesinvolvedindetectingthissignal,with

5、anemphasisontheGalacticandextragalacticforegrounds.Theseincreaserapidlytowardlowfrequenciesandareespeciallysevereforthehighestred-shiftapplications.Assumingthatthesedifficultiescanbeovercome,theredshifted21cmlinewillofferuniqueinsightintothehigh-redshiftUniverse,

6、complement-arXiv:astro-ph/0608032v220Sep2006ingotherprobesbutprovidingtheonlydirect,three-dimensionalviewofstructureformationfromz∼200toz∼6.Keywords:cosmology:theory–diffuseradiation–intergalacticmedium–line:formation–techniques:interferometricPACS:95.30.Dr;95.

7、85.Bh;98.62.Ra;98.70.Vc1Correspondingauthor.E-mail:steven.furlanetto@yale.edu.PreprintsubmittedtoElsevierScience3February2008Contents1Introduction41.1FromtheDarkAgestoReionization41.2HistoricalOverview111.3SomePreliminaries132FundamentalPhysicsofthe21cmLine202

8、.1BasicDefinitions202.2CollisionalCoupling252.3TheWouthuysen-FieldEffect322.4TheLymanSeries402.5Polarization422.6OtherHyperfineTransitions443TheGlobalEvolutionoftheIGM453.1TheDarkAges