Cosmological hydrodynamics [Elektronische Ressource] : thermal conduction and cosmic rays / vorgelegt von Martin Jubelgas

Martin Jubelgas

Sujets

• Astronomie

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2007
• Nombre de lectures: 31
• Poids de l'ouvrage: 5 Mo

Extrait

DissertationzumErlangendesakademischenGradesDoktorderNaturwissenschaften
derFakultätfürPhysikderLudwig-Maximilians-UniversitätMünchen
CosmologicalHydrodynamics: Thermal
ConductionandCosmicRays
vorgelegtvonMartinJubelgasausMünchen
München,19.12.2007
DissertationderFakultätfürPhysikder
Ludwig-Maximilians-UniversitätMünchenMartinJubelgas:
CosmologicalHydrodynamics: ThermalConductionandCosmicRays
DissertationderFakultätfürPhysikderLudwig-MaximiliansUniversitätMünchen
ausgeführtamMax-Planck-InstitutfürAstrophysik
Vorsitzender: Prof. Dr. ErwinFrey
1. Gutachter: Prof. Dr. SimonWhite
2. Gutachter: Prof. Dr. AndreasBurkert
WeitererPrüfer: Prof. Dr. RolandKersting
TagdermündlichenPrüfung: 19. März2007Contents
1. Introduction 1
1.1. (How)diditallstart? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Theearlyuniverseandthecosmicmicrowavebackground . . . . . . . . . . . . . . . . 4
1.3. Structureformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Galaxyformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2. Thesimulationcode 15
2.1. Collisionlessdynamicsandgravitation . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2. Hydrodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.1. BasicSPHconcepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.2. Theentropyequation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.3. Shocksandviscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3. Radiativeheatingandcooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4. Starformationandfeedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3. ThermalconductionincosmologicalSPHsimulations 35
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2. ThermalconductioninSPH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.1. Theconductionequation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.2. Spitzerconductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.3. SPHformulationofconduction . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.4. Numericalimplementationdetails . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3. Illustrativetestproblems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.3.1. Conductioninaone-dimensionalproblem . . . . . . . . . . . . . . . . . . . . . 45
3.3.2. Conductioninathree-dimensionalproblem . . . . . . . . . . . . . . . . . . . . 49
3.4. Sphericalmodelsforclustersofgalaxies . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.5. Cosmologicalclustersimulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4. Cosmicrayfeedbackinhydrodynamicalsimulationsofgalaxyformation 61
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.2. Thenatureofcosmicrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
iContents
4.2.1. Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2.2. Physicalprocesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.2.3. Amodelforcosmicrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.3. Modellingcosmicrayphysics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.3.1. Thecosmicrayspectrumanditsadiabaticevolution . . . . . . . . . . . . . . . 69
4.3.2. Includingnon-adiabaticCRprocesses . . . . . . . . . . . . . . . . . . . . . . . 73
4.3.3. Shockacceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.3.4. Injectionofcosmicraysbysupernovae . . . . . . . . . . . . . . . . . . . . . . 79
4.3.5. Coulombcoolingandcatastrophiclosses . . . . . . . . . . . . . . . . . . . . . 80
4.3.6. Equilibriumbetweensourceandsinkterms . . . . . . . . . . . . . . . . . . . . 83
4.4. Cosmicraydiffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.4.1. Modellingthediffusivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.4.2. Discretizingthediffusionequation . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.5. Numericaldetailsandtests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.5.1. Implementationissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.5.2. Shocksincosmicraypressurizedgas . . . . . . . . . . . . . . . . . . . . . . . 92
4.5.3. Cosmicraydiffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.6. Simulationsofisolatedgalaxiesandhalos . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.6.1. Formationofdiskgalaxiesinisolation . . . . . . . . . . . . . . . . . . . . . . . 97
4.6.2. Coolinginisolatedhalos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.7. Cosmologicalsimulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.7.1. Cosmicrayproductioninstructureformationshocks . . . . . . . . . . . . . . . 106
4.7.2. Dwarfgalaxyformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
4.7.3. Cosmicrayeffectsontheintergalacticmedium . . . . . . . . . . . . . . . . . . 115
4.7.4. Formationofclustersofgalaxies . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.7.5. Theinfluenceofcosmicraydiffusion . . . . . . . . . . . . . . . . . . . . . . . 119
4.8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5. Conclusions 127
Bibliography 131
iiInthespaceofonehundredandseventy-sixyearstheMississippihasshortened
itself twohundred and forty-twomiles. Therefore... in theOld SilurianPeriod
the Mississippi River was upward of one million three hundred thousand miles
long ... seven hundred and forty-two years from now the Mississippi will be
only a mile and three-quarters long. ... There is something fascinating about
science. One gets such wholesome returns of conjecture out of such a trifling
investmentoffact.
MarkTwain
1
Introduction
While working on this thesis, I was often asked: "Cosmology? What is it good for?". Perhaps under-
standably, it was often people focused on practical applications of science that asked the question. For
me, however, this was never a concern, because personally I consider cosmology to be one of the most
fascinatingfieldsofphysics. Asitdealswiththebeginningoftheuniverseandwiththeforcesthatdrove
cosmic evolution from the earliest times to what we observe today, cosmology addresses fundamental
human questions of "how did it all start" and "how will it all end". Cosmology tries to give reliable
scientific answers to questions that have always inspired mysticism, religion and the arts. Even in mod-
ern times, astronomical questions are a strong cultural driver, apparent by the widespread belief in the
foretellings of astrology. Given the role of ancient mysticism revolving around the sky and the celestial
objects, astronomy and cosmology might be considered the oldest branches of science, yet still offer
someofitsgreatestpuzzles. Thebeautyoftheskyandtheofthevisibleplanets,starsandremotegalax-
ies, observed by the naked eye or telescopes, has always amazed people and spurred their imagination.
Touching people emotionally like this, it is not surprising that there is a strong interest in this discipline
ofscienceinspiteofalackofdirecteconomicalmotivations.
Astrophysics is a field of science that draws on expertise from many different branches of physics, in-
cluding classic and comparatively well-understood processes like gravitation and basic hydrodynamics,
as well as modern fields of research like relativistic hydrodynamics and high-energy particle physics.
This diversity results in a uniquely comprehensive synopsis of different physical effects and their com-
bined action in an often highly complex network of interactions, typically in environments and physical
conditionsthatspanmanyordersofmagnitudesinphysicallength-,density-ortemperature-scales. The
universepresentsitselfasalaboratorythatallowsustostudyprocessesinrangesofphysicalparameters
that could hardly ever be generated on earth. Also, the sheer size of the universe gives us the chance to
1Introduction
Figure1.1.: The deployment of high-resolution instruments like the Space Telescope (HST, left panel) in
spacehasmadeitpossibletoobserveanunprecedentedlevelofdetailindistantobjects,e.g. the
EagleNebula,ayoungopenclusterintheSerpensCaudaconstellation. (Souce: NASA)
study rare events that occur among the large number of individual objects in this huge volume. Astro-
nomical observations also play an important role for particle physics, as they can be used to constrain
someofthefundamentalparametersinhigh-energyphysics,forexamplethemassesofneutrinos.
Whatcanbepercievedononehandasablessingforastrophysics,can,ontheotherhandbecalledone
of its biggest handicaps. Since these systems are far out o