Simulating star formation and turbulence in models of isolated disk galaxies [Elektronische Ressource] / Markus Hupp

Sujets

• Astronomie

Informations

• Publié par: julius-maximilians-universitat_wurzburg
• Publié le: 01 janvier 2009
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Markus Hupp
Simulating Star Formation
and Turbulence in Models of
Isolated Disk Galaxies
A FEARLESS Project
Fluid mEchanics with Adaptively Refined Large Eddy SimulationS
NGC 7331Doctoral Dissertation
Simulating Star Formation
and Turbulence in Models of
Isolated Disk Galaxies
A FEARLESS Project
Dissertation zur Erlangung des
naturwissenschaftlichen Doktorgrades
der Julius-Maximilians-Universität Würzburg
Markus Hupp
aus Würzburg
Institut für Theoretische Physik und Astrophysik
Fakultät für Physik und Astronomie
Universität Würzburg
Würzburg
Dezember 2008Eingereicht am:
bei der
Fakultät für Physik und Astronomie
Gutachter und Prüfer im Promotionsverfahren:
1. Gutachter Prof. Dr. Jens C. Niemeyer
2. Gutachter Prof. Dr. Karl Mannheim
der Dissertation
1. Prüfer Prof. Dr. Jens C. Niemeyer
2. Prüfer Prof. Dr. Karl Mannheim
3. Prüfer Prof. Dr. Thomas Trefzger
im Promotionskolloquium
Tag des Promotionskolloquiums:
Doktururkunde ausgehändigt am:Simulating Star Formation and Turbulence
in Models of Isolated Disk Galaxies
A FEARLESS Project
Fluid mEchanics with Adaptively Refined Large Eddy SimulationS
Gutachter / Referees:
Prof. Dr. Jens C. Niemeyer – Prof. Dr. Karl Mannheim
Abstract. We model Milky Way like isolated disk galaxies in high resolution three-dimensional hydrodynamical
simulations with the adaptive mesh refinement code Enzo. The model galaxies include a dark matter halo and
a disk of gas and stars. We use a simple implementation of sink particles to measure and follow collapsing
gas, and simulate star formation as well as stellar feedback in some cases. We investigate two largely different
realizations of star formation. Firstly, we follow the classical approach to transform cold, dense gas into stars
with an fixed efficiency. These kind of simulations are known to suffer from an overestimation of star formation
and we observe this behavior as well. Secondly, we use our newly developed FEARLESS approach to combine
hydrodynamical simulations with a semi-analytic modeling of unresolved turbulence and use this technique to
dynamicallydeterminethestarformationrate. Thesubgrid-scaleturbulenceregulatedstarformationsimulations
point towards largely smaller star formation efficiencies and henceforth more realistic overall star formation rates.
Moreworkisnecessarytoextendthismethodtoaccountfortheobservedhighlysupersonicturbulenceinmolecular
clouds and ultimately use the turbulence regulated algorithm to simulate observed star formation relations.
Key words. astrophysics - hydrodynamics - turbulence - star formation - simulation:subgrid-scale model -
ISM:turbulence - galaxies:formation:evolution:general
Abriss. IndieserArbeitbeschäftigenwirunsmitderModellierungundDurchführungvonhochaufgelöstendrei-
dimensionalen Simulationen von isolierten Scheibengalaxien, vergleichbar unserer Milchstraße. Wir verwenden
dazu den Simulations-Code Enzo, der die Methode der adaptiven Gitterverfeinerung benutzt um die örtliche und
zeitliche Auflösung der Simulationen anzupassen. Unsere Galaxienmodelle beinhalten einen Dunkle Materie Halo
sowie eine galaktische Scheibe aus Gas und Sternen. Regionen besonders hoher Gasdichte werden durch Teilchen
ersetzt, die fortan die Eigenschaften des Gases beziehungsweise der darin entstehenden Sterne beschreiben. Wir
untersuchen zwei grundlegend verschiedene Darstellungen von Sternentstehung. Die erste Methode beschreibt die
Umwandlung dichten Gases einer Molekülwolke in Sterne mit konstanter Effektivität und führt wie in früheren
SimulationenzueinerÜberschätzungderSternentstehungsrate. DiezweiteMethodenutztdasvonunsererGruppe
neu entwickelte FEARLESS Konzept, um hydrodynamische Simulationen mit analytischen-empirischen Modellen
zu verbinden und bessere Aussagen über die in einer Simulation nicht explizit aufgelösten Bereiche treffen zu kön-
nen. Besonderes Augenmerk gilt in dieser Arbeit dabei der in Molekülwolken beobachteten Turbulenz. Durch die
EinbeziehungdiesernichtaufgelöstenEffektesindwirinderLageeinerealistischereAussageüberdieSternentste-
hungsrate zu treffen. Eine zukünftige Weiterentwicklung dieser von uns entwickelten und umgesetzten Technik
kann in Zukunft dafür verwendet werden, die Qualität des durch Turbulenz regulierten Sternentstehungsmodells
noch weiter zu steigern.
Schlagwörter. Astrophysik - Hydrodynamik - Turbulenz - Sternentstehung - Simulation:Subgrid-Skalen Modell -
ISM:Turbulenz - Galaxien:Entstehung:Entwicklung:Allgemein
Würzburg, December 2008Simulating Star Formation and Turbulence
in Models of Isolated Disk Galaxies
This thesis is based upon the following publications:
I FEARLESS – A new modelling approach for turbulent astrophysical flows
W. Schmidt, A. Maier, M. Hupp, L. Iapichino and J. C. Niemeyer; Astronomische Nachrichten 328:
663-+, 2007;
I FEARLESS* – Subgrid-Scale Turbulence modeling and Applications to Star Formation
M.Hupp,A.Maier,J.C.Niemeyer,W.Schmidt,L.Iapichino,J.AdamekandC.Federrath; Astronomis-
che Nachrichten 328: 664-+, 2007;
I Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas
W. Schmidt, C. Federrath, M. Hupp, S. Kern, J. C. Niemeyer; Astronomy and Astrophysics, accepted
by A&A, 2008;
I Simulating Star Formation and Turbulence in Models of Isolated Disk Galaxies
M. Hupp, W. Schmidt, A. Maier, J. C. Niemeyer; in preparation;
The work contained in this thesis is part of the research done within the DFG-funded International
Research Training Group (GRK 1147/1) entitled as Theoretical Astrophysics and Particle Physics. This
graduate school is a joint project of the Department of Physics (Theoretical Astrophysics and Theoret-
ical High Energy Physics) and the Department of Mathematics of the Julius-Maximilians-Universität
Würzburg; it is funded by the Deutsche Forschungsgemeinschaft (DFG) and so was the author.
GRK 1147/1
PhD thesis
Author: Markus Hupp
E-mail address: [e-mail]
Typeface: Computer Modern Roman 8pt, 9pt, 10pt, 11pt, 12pt
A ADistribution: LT X2 usingA SLT X and hyperrefεE M E
Compiled on February 26, 2009 as a native dvi documentvContents
Notation 1
Preface 5
Part I. Nursery of Stars 9
Chapter 1. Motivation 11
1.1. Introduction 11
1.2. Goals of this Thesis 13
Chapter 2. Star Formation in Disk Galaxies 15
2.1. Hydrodynamical Framework 15
2.2. The Formation of Galaxies 17
2.3. Disk Galaxies 18
2.4. The Interstellar Medium 20
2.5. Giant Molecular Clouds and Star Formation 22
Chapter 3. Major Physical Processes in Star Formation 25
3.1. From Molecular Clouds towards the Initial Mass Function 25
3.2. The Virial Theorem 26
3.3. Gravitational Potential 27
3.4. Thermal Pressure 27
3.5. Magnetic Fields 28
3.6. Kinetic Energy and Turbulence 29
3.7. Uncertainties and Errors 30
Chapter 4. Nature and Effects of Turbulence 33
4.1. A Brief Summary of Incompressible Turbulence 33
4.2. Turbulence in the Interstellar Medium 35
4.3. Driving and Effect of Supersonic Turbulence 36
4.4. Turbulence Regulated Star Formation 38
Summary of Theory 43
Part II. Toy Models and the Playground 45
Chapter 5. The Simulation Framework 47
5.1. The Hydrodynamics Code Enzo 47
5.2. The Zeus Algorithm and its Implementation 48
5.3. Thermodynamical Processes and their Realization 53
5.4. Sink Particle Implementation 56
5.5. Star Formation Rate and Feedback 59
Chapter 6. Setting up an Isolated Disk Galaxy 61
6.1. Cosmological Framework and Dark Matter Halo 61
viiviii CONTENTS
6.2. The Baryonic Gas Disk 63
6.3. Amendments to Star Formation and Feedback Algorithms 67
Chapter 7. Turbulence and Subgrid-Scale Physics 71
7.1. The Subgrid-Scale Model 71
7.2. Closures for the Production of Turbulence Energy 76
7.3. Subgrid-Scale Physics on an Adaptive Mesh 78
7.4. SGS Model Specialties for Galaxy Simulations 79
Chapter 8. Density Distribution of Gas in Star Forming Regions 81
8.1. The Lognormal distribution 81
8.2. Compressively Driven Interstellar Turbulence 83
8.3. Deviations from the Lognormal Distribution of Gas Densities 85
8.4. The Density Distribution in the Star Formation Algorithm 86
Summary of Numerics 89
Part III. Learning from Simulations 91
Chapter 9. Results of Numerical Simulations 93
9.1. Redefining Initial Conditions 93
9.2. Summary of Performed Simulations 96
9.3. Evolution of the Gas Disk 96
9.4. Dynamics of Thermal Properties 101
9.5. The Formation of Stars 106
9.6. Effects from Stellar Feedback 109
9.7. Modifications to the Standard Case 114
Chapter 10. Turbulence Regulated Star Formation 119
10.1. The Efficiency Parameter 119
10.2. Simulations with Reduced Efficiency 121
10.3. Galaxy Simulation with Subgrid Physics but No Coupling to Star Formation 124
10.4. Turbulence Regulated Star Formation with Limited Turbulent Mach Number 127
10.5. Low Turbulence Mach Number Regulated Galaxy Simulation with Feedback 132
10.6. Thermal and Turbulent Pressure in the Galactic Disk 141
Chapter 11. Conclusions and Prospects 145
11.1. Simulation of Galactic Disk Systems 145
11.2. Shortcomings, Achievements and Future Projects 145
11.3. Concl