Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality: Saas-Fee Advanced Course 43. Swiss Society for Astrophysics and Astronomy

375 Pages·2016·12.44 MB·English

by  Nickolay Y. Gnedin

Saas-Fee Advanced Course 43
Swiss Society for Astrophysics and Astronomy
Nickolay Y. Gnedin
Simon C.O. Glover
Ralf S. Klessen
Volker Springel
Star Formation in
Galaxy Evolution:
Connecting
Numerical Models
to Reality
Saas-Fee Advanced Course 43
More information about this series at http://www.springer.com/series/4284
Nickolay Y. Gnedin Simon C.O. Glover
(cid:129)
Ralf S. Klessen Volker Springel
(cid:129)
Star Formation in Galaxy
Evolution: Connecting
Numerical Models to Reality
Saas-Fee Advanced Course 43
Swiss Society for Astrophysics and Astronomy
Edited by Yves Revaz, Pascale Jablonka, Romain Teyssier
and Lucio Mayer
123
NickolayY.Gnedin VolumeEditors
DepartmentofAstronomyandAstrophysics YvesRevaz
TheUniversityofChicago Laboratoired’astrophysique
Chicago,IL ÉcolePolytechniqueFédéraledeLausanne(EPFL)
USA ObservatoiredeSauverny
Versoix
SimonC.O.Glover Switzerland
InstituteforTheoreticalAstrophysics
PascaleJablonka
UniversityofHeidelberg Laboratoired’astrophysique
Heidelberg ÉcolePolytechniqueFédéraledeLausanne(EPFL)
Germany
ObservatoiredeSauverny
Versoix
RalfS.Klessen Switzerland
InstituteforTheoreticalAstrophysics
UniversityofHeidelberg RomainTeyssier
Heidelberg CenterforTheoreticalAstrophysicsandCosmology
Germany InstituteforComputationalScience
UniversityofZurich
VolkerSpringel Zurich
ZAH,ARI Switzerland
HeidelbergUniversity
LucioMayer
Heidelberg
CenterforTheoreticalAstrophysicsandCosmology
Germany
InstituteforComputationalScience
UniversityofZurich
Zurich
Switzerland
This Series is edited on behalf of the Swiss Society for Astrophysics and Astronomy: Société Suisse d’Astrophysique et
d’Astronomie,ObservatoiredeGenève,ch.desMaillettes51,CH-1290Sauverny,Switzerland
Coverfigure:Cygnus-Xisanextremelyactiveregionofmassive-starbirthsome4500light-yearsfromEarthintheconstellation
ofCygnus,theSwan.Thispicture,takenbyHerschel’sfar-infraredcamera(Credit:ESA),illustratethecomplexityofthestar
formationoutofturbulentclouds.ItissuperimposedonthelowerrightbytheMönchsupercomputerhostedattheSwissNational
SupercomputingCenter(CSCS)inLugano,Switzerland(Credit:CSCS),andontheupperleftbythespiralgalaxyNGC1232
(Credit:ESO)obtainedbytheFORS(FOcalReducerandlowdispersionSpectrograph)instrumentonthe8metersVeryLarge
TelescopeatParanal,Chile(Montage,Credit:EPFL/YvesRevaz).
ISSN 1861-7980 ISSN 1861-8227 (electronic)
Saas-FeeAdvancedCourse
ISBN978-3-662-47889-9 ISBN978-3-662-47890-5 (eBook)
DOI10.1007/978-3-662-47890-5
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SpringerHeidelbergNewYorkDordrechtLondon
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Preface
In the last few years it has become clear that the modelling of star formation and
feedbackprocessesiscentraltothequestoffindingsolutionstothekeyproblemsof
galaxy formation. A complete story of star formation and its connection with the
cosmicevolutionofourUniverserequirestostudyphysicalprocessestakingplace
at very different scales.
At cosmological scales the gas is sparse and highly ionized. Its temperature
depends on the subtle balance between photo-heating and adiabatic as well as
radiativecooling.Inthedensestregions, followingthegrowthofthecosmological
fluctuations,itmaybeaccretedontoformingandevolvinggalaxies.Atthegalactic
scale,thephysicsbecomesextremelycomplex,non-linearandfarfromequilibrium.
The interstellar medium is composed of a mixture of charged particles, atoms,
molecules and dust grains. There, turbulent cascades drive the formation of cloud
complexesofvarioussizesandmasses,fromwhichstarsmayeventuallyform.The
collapse of these complexes is ultimately halted by star formation, resulting in a
system intricately linked together through a variety offeedback loops.
Due to the numerous complex and interleaved process involved, modelling the
star formation is challenging. The theory and numerical models of star formation
have traditionally evolved independently from those of galaxy evolution, because
theyactatdifferentspatialscales.Wearenowatapointhowever,wheresubstantial
steps forward can only arise from the combined knowledge of these two research
fields.
The goal of the 43rd Saas-Fee Advanced Course was to bring together, in a
singleplace,thesetwofields.Itaimedtotakeaninventoryofthephysicalprocesses
related to the star formation involved at different scales and also to provide an
overview of the major computational techniques used to solve the equations gov-
erningself-gravitatingfluids,essentialtogalacticmodelling.Togetherthisprovides
a unique framework essential to developing and improving the simulation tech-
niques used to understand the formation and evolution of galaxies.
The lack of a textbook joining these different fields motivated the members
of the Swiss Society for Astrophysics and Astronomy to vote in favour of the
v
vi Preface
organisation of a winter Saas-Fee course on the star formation in galaxies and its
modelling techniques.
The three selected lecturers—Nickolay Gnedin, Ralf Klessen and Volker
Springel—succeeded in bringing to the 95 participants a very rich and interesting
review of the fields related to the star formation in galaxies. An invaluable
additional contribution came later from Simon Glover who participated in the
writingofthechapterdedicatedtothephysicalprocessesintheinterstellarmedium.
Thereadercanrevelnowthoselecturesinthefollowingpages.Thepresentbookis
supplemented with the complete video recordings of the lectures, which are
accessible online, via the 43rd Saas-Fee Advanced Course website: http://lastro.
epfl.ch/conferences/sf2013/.
We are very grateful to the lecturers for their invaluable live lectures as well
as for their written version presented here. We are particularly thankful to
Prof. Georges Meylan, Head of the Laboratory of Astrophysics at EPFL, who
supported the organisation at all stages, making this course a success. We are
extremely grateful to Matthew Nichols, who video-recorded the lectures and
post-processed the movies. Olivier Genevay has been at the heart of all practical
arrangements without counting his time; we want to thank him very warmly. We
also thank the course secretaries, Carol Maury and Claire Schatzmann, as well as
our colleagues, Malte Tewes, Vivien Bonvin, Alexis Arnaudon and Daniel
Pfenniger for all their help in the practical organisation of the course.
The course took place during winter in the village of Villars-sur-Ollon in the
AlpsofSwitzerland.Whilebenefitingfromsuperbweatheraftersomesnowydays,
a conference picture was kindly taken by Ievgen Vovk and is displayed below.
Yves Revaz
Pascale Jablonka
Romain Teyssier
Lucio Mayer
Preface vii
Contents
Modeling Physical Processes at Galactic Scales and Above . . . . . . . . . 1
Nickolay Y. Gnedin
1 In Lieu of Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Physics of the IGM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Linear Hydrodynamics in the Expanding Universe. . . . . . . . . . . 2
2.2 Lyman-α Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Modeling the IGM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 What Observations Tell Us. . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3 From IGM to CGM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1 Large Scale Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 How Gas Gets onto Galaxies. . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Cool Streams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.4 Galactic Halos. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.5 Diversion: Cooling of Rarefied Gases. . . . . . . . . . . . . . . . . . . . 29
3.6 Back to Galactic Halos. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4 ISM: Gas in Galaxies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.1 Galaxy Formation Lite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.2 Galactic Disks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3 Ionized, Atomic, and Molecular Gas in Galaxies . . . . . . . . . . . . 44
4.4 Molecular ISM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5 Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.1 Kennicutt-Schmidt and All, All, All. . . . . . . . . . . . . . . . . . . . . 63
5.2 Excursion Set Formalism in Star Formation. . . . . . . . . . . . . . . . 70
6 Stellar Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.1 What Escapes from Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.2 Unconventional Marriage: Feedback and Star Formation. . . . . . . 77
6.3 Toward the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7 Answers to Brain Teasers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
ix
x Contents
Physical Processes in the Interstellar Medium. . . . . . . . . . . . . . . . . . . 85
Ralf S. Klessen and Simon C.O. Glover
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
2 Composition of the ISM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
2.1 Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
2.2 Dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
2.3 Interstellar Radiation Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
2.4 Cosmic Rays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3 Heating and Cooling of Interstellar Gas . . . . . . . . . . . . . . . . . . . . . . 100
3.1 Optically-Thin Two-Level Atom . . . . . . . . . . . . . . . . . . . . . . . 100
3.2 Effects of Line Opacity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.3 Multi-level Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
3.4 Atomic and Molecular Coolants in the ISM. . . . . . . . . . . . . . . . 110
3.5 Gas-Grain Energy Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
3.6 Computing the Dust Temperature. . . . . . . . . . . . . . . . . . . . . . . 123
3.7 Photoelectric Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
3.8 Other Processes Responsible for Heating. . . . . . . . . . . . . . . . . . 127
4 ISM Turbulence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.1 Observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.2 Simple Theoretical Considerations . . . . . . . . . . . . . . . . . . . . . . 142
4.3 Scales of ISM Turbulence. . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
4.4 Decay of ISM Turbulence. . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
4.5 Sources of ISM Turbulence: Gravity and Rotation. . . . . . . . . . . 153
4.6 Sources of ISM Turbulence: Stellar Feedback . . . . . . . . . . . . . . 158
5 Formation of Molecular Clouds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
5.1 Transition from Atomic to Molecular Gas. . . . . . . . . . . . . . . . . 164
5.2 Importance of Dust Shielding . . . . . . . . . . . . . . . . . . . . . . . . . 175
5.3 Molecular Cloud Formation in a Galactic Context . . . . . . . . . . . 178
6 Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
6.1 Molecular Cloud Cores as Sites of Star Formation. . . . . . . . . . . 183
6.2 Statistical Properties of Stars and Star Clusters . . . . . . . . . . . . . 189
6.3 Gravoturbulent Star Formation. . . . . . . . . . . . . . . . . . . . . . . . . 194
6.4 Theoretical Models for the Origin of the IMF . . . . . . . . . . . . . . 196
6.5 Massive Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
6.6 Final Stages of Star and Planet Formation. . . . . . . . . . . . . . . . . 211
7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
High Performance Computing and Numerical Modelling. . . . . . . . . . . 251
Volker Springel
1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
2 Collisionless N-Body Dynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
2.1 The Hierarchy of Particle Distribution Functions . . . . . . . . . . . . 252
2.2 The Relaxation Time—When Is a System Collisionless?. . . . . . . 255