From First Light to Reionization - The End of the Dark Ages [astrophysics]

231 Pages·2009·5.223 MB·English

by  M. Stiavelli

MassimoStiavelli
FromFirstLighttoReionization
Foradditionalinformation
reagarding thistopic,pleasereferalso
tothefollowingpublications
Phillipps,S.
TheStructure andEvolutionofGalaxies
2005
ISBN978-0-470-85507-2
Stahler,S.W.,Palla,F.
TheFormationofStars
2004
ISBN978-3-527-40559-6
Roos,M.
IntroductiontoCosmology
2003
ISBN978-0-470-84910-1
Liddle,A.
AnIntroductiontoModernCosmology
2003
ISBN978-0-470-84835-7
Shore,S.N.
TheTapestry ofModernAstrophysics
2003
ISBN978-0-471-16816-4
Coles,P.,Lucchin,F.
Cosmology
TheOriginandEvolutionofCosmicStructure
2002
ISBN978-0-471-48909-2
Massimo Stiavelli
From First Light to Reionization
The End of the Dark Ages
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V
Preface
Decidingwhetheratopicisreadytobecometextbookmaterialcanbeajudgement
calland,sometimes,agamble.Thelatterisespeciallytruewhenafieldisevolving
rapidlythankstoexperimentalandtheoreticaladvances.Thestudyofthehighest-
redshiftfrontierhasbeen oneofthemostexcitingareasofastronomyinthelast
decade.Improvedobservationaltoolssuchaslargeground-basedtelescopesofthe
8–10m classandtheHubbleSpace Telescope allowedustopush thisfrontierto
redshift6andbeyond.Wearenowfinallyatthepointofbeingabletoaddressthe
formationofthefirststarsandtostudytheobjectsresponsibleandthechronology
ofthereionizationofhydrogen.Thisrepresents,inasense,theboundaryofclas-
sicalastronomy.TheUniversebeforereionizationandbeforetheformationofthe
firststarswasindeedaverydifferentplace.Weexpectthatnewfacilitiessuchasthe
Wide-FieldCamera3tobeinstalledontheHubbleSpaceTelescopeduringServic-
ingMission4and,especially,theJamesWebb SpaceTelescopewillenablemajor
observationalprogressinthisareaandthefloodofnewobservationalresultswill
mostlikelystimulatefurthertheoreticalprogress.
Giventhispositiveoutlookandgreatexpectationsofprogressonemightwonder
whyitisagoodideatowriteatextbookonsuchafast-evolvingtopic.Thereasons
areseveral.Oneisthatafieldthatislivelyattractstheattentionofmanyobservers
andtheoristsanditislikelythatmanystudentswillworkinthisfieldinthecoming
decade.However,thebulkoftheworkalreadydoneisverysignificantand–before
westartedthisenterprise–nograduate-leveltextbookgaveanoverviewofthestate-
of-the-artonboththeoryandobservationssoastoenableyoungresearcherstoget
quickly up to speed in this field of research. Another reason is that despite the
manyunknowns,someofthepresentthinkingregardingtheformationofthefirst
starsand reionizationisdeeply rooted inphysical argumentsso that,even ifthe
detailschange,manyofthegeneralprinciplesshouldremainapplicable.Thistopic
reliesonresultsfrommanybranchesofphysicsrangingfromcosmologytoatomic
physicsandchemicalreactions,sothatprovidingasimplebutreasonablycomplete
overview of these various aspects can be useful not only to students but also to
activeresearchersspecializedinotherareasofastronomywhomaybeexpertsin
someofthesubareasbutnotinothers.
AsanEditoroftheWileyCosmologyseriesmyfirstthoughtwastofindsuitable
authorsfor thisbook but unfortunatelyit is hard to find top researchers actively
VI Preface
engaged in a field willingto pause and write a book of thisnature. After several
unsuccessful attemptsI decided totry myself andIdo notregret it.Writingthis
bookcertainlytookalotofeffortbutwasalsointerestingandveryrewardingandI
learnedalotintheprocess.
Ihaveattemptedtocapturewhatappeartobethemostsolidresultsandconcepts.
IntheefforttocollectthematerialandtheideasforthisbookIhaveprofitedfrom
discussions with many colleagues includingTom Abel, Mike Fall,XhiahouiFan,
HarryFerguson,ZoltanHaiman,PeterJakobsen,SimonLilly,AviLoeb,ColinNor-
man,NinoPanagia,PaulShapiro,MikeShull,PeterStockman,RogierWindhorst,
Rosie Wyse. In writing the theoretical chapters of this book I have enjoyed daily
interactionsanddiscussionswithMicheleTrenti.Afractionofthisworkwasdone
during a sabbatical year spent at Johns Hopkins University. My wife, Francesca
Boffi,contributedherpatienceandunderstanding,whichwerecrucialforthecom-
pletionofthisproject.
Baltimore,September2008 MassimoStiavelli
VII
Contents
Preface V
1 Introduction 1
1.1 FirstLightandReionization 1
1.2 TheCosmologicalFramework 2
1.3 OrganizationofthisBook 2
1.4 KeyObservationsinthisField 4
Part1 Theory 5
2 TheFirstStars 7
2.1 Overview 7
2.1.1 FirstLight 7
2.1.2 FormingtheFirstStars 8
2.1.3 TheLegacyoftheFirstStars 9
2.2 BeforetheFirstStars 9
2.2.1 RecombinationandResidualIonizationFraction 9
2.2.2 TheFormationofMolecularHydrogen 13
2.2.3 CoolingFunctions 16
2.3 FormingtheFirstStars 18
2.3.1 PerturbationsintheEarlyUniverse 18
2.3.2 CollapseofPerturbationsintheEarlyUniverse 21
2.3.3 CoolingandtheJeansInstability 25
2.3.4 PropertiesoftheFirstStars 31
2.3.5 RemnantsandSignaturesofaPopulationIII 34
2.4 PrimordialHIIRegions 35
2.5 WhatifDarkMatterisnotCold? 37
2.6 HintsforFurtherStudy 38
3 TheFirstStarClustersandGalaxies 39
3.1 Overview 39
3.2 SubsequentGenerationsofStars 39
3.2.1 Second-GenerationPopulationIIIStars 40
3.2.2 PopulationIIIStarsForminginSelf-ShieldingHalos 41
VIII Contents
3.2.3 LatePopulationIIIStarFormationbyAtomic-HydrogenCooling
inMassiveHalos 48
3.2.4 TerminationoftheFirstStarsPhase 49
3.3 ContainingGasintheHalosofPopulationIIIStars 49
3.3.1 IonizationHeatingandGasTemperature 49
3.3.2 TheEscapeofGasHeatedbyIonization 53
3.3.3 TheEscapeofGasFollowingaSupernovaExplosion 56
3.3.4 PopulationII.5 58
3.4 TheFirstStarClusters 59
3.4.1 ClustersofPopulationIIIStarsandofMetal-PoorStars 61
3.4.2 TheOriginofGlobularClusters 62
3.5 TheFirstGalaxies 63
3.6 TheFirstActiveGalacticNuclei 64
3.6.1 PopulationIIIBlackHoles 64
3.6.2 Black-HoleMergers 65
3.6.3 TheHighest-RedshiftQSOs 66
3.6.4 DirectCollapsetoBlackHoles 67
3.7 Low-MetallicityHIIRegions 67
3.8 NumericalTechniquesandTheirLimitations 68
3.8.1 CollisionlessDynamics 68
3.8.2 CollisionlessDynamics:Particle-MeshCodes 70
3.8.3 CollisionlessDynamics:Treecodes 71
3.8.4 GasDynamics 71
3.8.5 GasDynamics:SmoothParticleHydrodynamics 72
3.8.6 GasDynamics:EulerianCodes 72
3.8.7 ImprovingResolutionThroughMeshRefinement 73
3.8.8 RadiativeTransfer 73
3.9 HintsforFurtherStudy 73
4 CosmicReionization 75
4.1 Overview 75
4.2 ThePropertiesoftheSourcesofReionization 76
4.2.1 TheSurfaceBrightnessofReionizationSources 77
4.2.2 ReionizationinaHydrogen-OnlyIGM 79
4.2.3 ReionizationinaHydrogen–HeliumIGM 80
4.2.4 ResultsforaHomogeneousIGM 81
4.2.5 MeanMetallicityatReionization 83
4.3 AddingRealismtotheCalculations 85
4.3.1 EscapeofIonizingPhotons 85
4.3.2 ClumpyIGM 88
4.3.3 Two-ParameterModels 90
4.4 LuminosityFunctionofIonizingSources 90
4.4.1 DetectingLymanαfromIonizingSources 92
4.5 ReionizationbyPopulationIIIStars 95
4.6 HowIstheIntergalacticMediumEnriched? 96
Contents IX
4.7 ReheatingoftheIntergalacticMedium 97
4.8 KeepingtheIntergalacticMediumIonized 98
4.9 HintsforFurtherStudy 100
Part2 ObservationalTechniquesandtheirResults 101
5 StudyingtheEpochofReionizationofHydrogen 103
5.1 Overview 103
5.2 Gunn–PetersonTroughsinRedshift6QSOs 104
5.2.1 ASimpleGunn–PetersonTest 104
5.2.2 TheGunn–PetersonTrough 106
5.2.3 LymanSeriesLines 108
5.2.4 MetalLines 109
5.2.5 HIIRegionSizeTest 109
5.2.6 DarkGaps 110
5.2.7 AnAssessmentoftheIndicationfromQSOsSpectra 110
5.3 LymanαSourcesasDiagnosticsofReionization 111
5.3.1 EffectofaFiniteLymanαLineWidth 111
5.3.2 IntrinsicPropertiesofLymanαEmitters 111
5.3.3 EffectofaLocalIonizedBubble 114
5.3.4 ARealisticLymanαEscapeModel 115
5.3.5 PerspectivesonStudyingReionizationwithLymanαSources 117
5.3.6 FaintLymanαHalos 119
5.4 Neutral-HydrogenSearches 121
5.4.1 OtherApplicationsofHigh-z21-cmObservations 124
5.5 ComptonOpticalDepth 126
5.6 LymanαSignatureintheDiffuseNear-IRBackground 127
5.7 HintsforFurtherStudy 128
6 TheFirstGalaxiesandQuasars 129
6.1 Overview 129
6.2 TheLyman-BreakTechnique 129
6.2.1 TheLymanBreakasaFunctionofRedshift 130
6.2.2 SyntheticStellarPopulationModels 131
6.2.3 Redshift6DropoutGalaxies 132
6.2.4 Lyman-BreakGalaxiesatRedshiftGreaterthan6 133
6.3 TheLymanαExcessTechnique 135
6.4 TheBalmer-JumpTechnique 136
6.4.1 AnOldGalaxyatLoworHighRedshift? 137
6.5 PhotometricRedshifts 139
6.6 SamplesofHigh-RedshiftGalaxies 141
6.6.1 Lyman-BreakGalaxiesatz=6 141
6.6.2 Lyman-BreakGalaxiesatz>7 143
6.6.3 LymanαEmitters 144
6.6.4 High-RedshiftQSOs 146
6.7 Fluctuations 147