Constraining the UV background with the proximity effect [Elektronische Ressource] / Aldo Dall'Aglio

Aldo Dall'Aglio

Sujets

• Astronomie

Informations

• Publié par: universitat_potsdam
• Publié le: 01 janvier 2009
• Nombre de lectures: 24
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

ConstrainingtheUVbackground
withtheproximityeffect
AldoDall’Aglio
AstrophysikalischesInstitutPotsdam
DissertationzurErlangungdesakademischenGrades
doctorrerumnaturalium(Dr. rer.nat.)
inderWissenschaftsdisziplinAstrophysik
¨EingereichtanderMathematisch-NaturwissenschaftlichenFakultat
derUniversita¨tPotsdam
Mai2009













































Published online at the
Institutional Repository of the University of Potsdam:
URL http://opus.kobv.de/ubp/volltexte/2009/3871/
URN urn:nbn:de:kobv:517-opus-38713
http://nbn-resolving.org/urn:nbn:de:kobv:517-opus-38713 Dedica
Questo lavoro e’dedicato alle Scelte,
a quell’invisibile disequilibrio
che ci porta ad intraprendere
sentieri sconosciuti perfarci diventare
quello che siamo oggi.
AldoContents
Abstract 7
Zusammenfassung 9
1 Introduction 11
1.1 Theconcordancemodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2 Structuregrowthin thehighredshiftUniverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3 Theintergalacticmedium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4 Theionisationstateoftheintergalacticmedium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.5 Theproximityeffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.6 Outlineandstructureofthework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2 AnunbiasedmeasurementoftheUVbackgroundanditsevolutionviatheproximityeffectinquasarspectra 21
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3 MonteCarlosimulationsofartificialspectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4 EvolutionoftheLyαeffectiveopticaldepth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.5 Methodsofquantifyingtheproximityeffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.6 Theproximityeffectinthecombinedsampleofquasars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.7 Theproximityeffectinindividuallinesofsight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.8 Theroleofoverdensitiesaroundquasars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.9 TheredshiftevolutionoftheUVbackground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3 The UVbackgroundphotoionisationrateat2.3≤ z≤ 4.6asmeasuredfromtheSloanDigitalSkySurvey 39
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2 TheQuasarSample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3 MonteCarlosimulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.4 Aquasarcompositespectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5 EffectiveopticaldepthoftheLyαforest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.6 Measurementsoftheproximityeffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.7 TheevolutionoftheUVbackgroundphotoionisationrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.8 OriginofthemetagalacticUVphotons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4 Analysisofmethodsfordetectingtheproximityeffectinquasarspectra 55
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.2 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3 TheLymanforest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.4 Theproximityeffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.5 Methodsofestimatingtheproximityeffectstrength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5 Radiativetransferandtheline-of-sightproximityeffect 69
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.2 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.3 Definitionsandprocedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.4 Systematicuncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6 ConclusionsandOutlook 75
6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.2 Prospectsforfuturestudies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76A Analyticalderivations 79
A.1. Thephotoionisationstateoftheintergalacticmedium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
A.2. Thefluxtransmissiontechnique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
A.3. Thecosmologicalradiativetransfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
B TheproximityeffectonindividuallinesofsightintheUVESsampleofquasars 85
C Errorassessmentofthehigh-zUVbackgroundderivedfromSDSS 89
C.1. DeterminationofthequasarLymanlimitluminosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
C.2. Redshiftdetermination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
C.3. Definitionofthequasarcontinuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
C.4. Signaltonoiselevel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Acknowledgements 93Abstract
After the epoch of reionisation the intergalactic medium (IGM) is kept at a high photoionisation level by the
cosmicUVbackgroundradiationfield.Primarilycomposedoftheintegratedcontributionofquasarsandyoungstar
forminggalaxies,itsintensityissubjecttospatialandtemporalfluctuations.Inparticularinthevicinityofluminous
quasars,theUVradiationintensitygrowsbyseveralordersof magnitude.Dueto anenhancedUV radiationup to
afewMpcfromthequasar,theionisedhydrogenfractionsignificantlyincreasesandbecomesvisibleasareduced
levelofabsorptionintheHLymanalpha(Lyα)forest.Thisphenomenonisknownastheproximityeffectanditis
themain focusof thisthesis. ModellingtheinfluenceontheIGMofthequasarradiation,oneisabletodetermine
the UV background intensity at a specific frequency (J ), or equivalently, its photoionisation rate (Γ ). This isν b0
of crucial importance for both theoretical and observational cosmology. Thus far, the proximity effect has been
investigatedprimarilyby combiningthe signal of largesamples of quasars, as it has been regardedas a statistical
phenomenon.Only a handfulof studies tried to measure its signatureon individuallines of sight, albeit focusing
on one sight line only. Our aim is to perform a systematic investigationof large samples of quasars searching for
thesignatureoftheproximityeffect,withaparticularemphasisonitsdetectiononindividuallinesofsight.
We begin this survey with a sample of 40 high resolution (R ∼ 45000), high signal to noise ratio (S/N ∼ 70)
quasar spectra at redshift 2.1 < z < 4.7, publicly available in the EuropeanSouthern Observatory(ESO) archive.
Theextraordinaryqualityofthisdatasetenablesustodetecttheproximityeffectsignaturenotonlyinthecombined
quasarsample, butalso alongeach individualsightline. Thisallows usto determinenotonly theUVbackground
intensityatthemeanredshiftofthissample, butalso to estimateits intensityin small(Δz∼ 0.2)redshiftintervals
−22 −1 −2 −1 −1< <in the range 2 z 4. Our estimates (J ∼ 3 × 10 erg s cm Hz sr ) are for the first time in very∼ ∼ ν0
good agreement with different constraints of its evolution obtained from theoretical predictions and numerical
simulations.
We continue this systematic analysis of the proximity effect with the largest sear