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

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

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 LibraryofCongressControlNumber:2015944146 SpringerHeidelbergNewYorkDordrechtLondon ©Springer-VerlagBerlinHeidelberg2016 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartofthematerialisconcerned, specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation,broadcasting,reproductiononmicrofilmsorin anyotherphysicalway,andtransmissionorinformationstorageandretrieval,electronicadaptation,computersoftware,orby similarordissimilarmethodologynowknownorhereafterdeveloped. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublicationdoesnotimply,evenin theabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevantprotectivelawsandregulationsandtherefore freeforgeneraluse. Thepublisher,theauthorsandtheeditorsaresafetoassumethattheadviceandinformationinthisbookarebelievedtobetrue andaccurateatthedateofpublication.Neitherthepublishernortheauthorsortheeditorsgiveawarranty,expressorimplied, withrespecttothematerialcontainedhereinorforanyerrorsoromissionsthatmayhavebeenmade. Printedonacid-freepaper Springer-VerlagGmbHBerlinHeidelbergispartofSpringerScience+BusinessMedia(www.springer.com) 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

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