The Origin of the Galaxy and Local Group: Saas-Fee Advanced Course 37 Swiss Society for Astrophysics and Astronomy PDF
Preview The Origin of the Galaxy and Local Group: Saas-Fee Advanced Course 37 Swiss Society for Astrophysics and Astronomy
Saas-Fee Advanced Course 37 Swiss Society for Astrophysics and Astronomy Joss Bland-Hawthorn Kenneth Freeman Francesca Matteucci The Origin of the Galaxy and Local Group Saas-Fee Advanced Course 37 For furthervolumes: http://www.springer.com/series/4284 Joss Bland-Hawthorn Kenneth Freeman • Francesca Matteucci Ben Moore • The Origin of the Galaxy and Local Group Saas-Fee Advanced Course 37 Swiss Society for Astrophysics and Astronomy Edited by B. Moore 123 Joss Bland-Hawthorn Francesca Matteucci SydneyInstitutefor Astronomy AstronomyDepartment Universityof Sydney Trieste University Osservatorio Sydney, NSW Astronomico(INAF) Australia Trieste Italy Kenneth Freeman Australian National University Volume Editor Australian CapitalTerritory, ACT BenMoore Australia InstituteforTheoretical Physics Universityof Zürich Zürich Switzerland This Series is edited on behalf of the Swiss Society for Astrophysics and Astronomy: Société Suissed’Astrophysiqueetd’AstronomieObservatoiredeGenève,ch.desMaillettes51,CH-1290 Sauverny,Switzerland CoverIllustration:ThecoverimageshowstheAndromedagalaxysuperimposedovertheMönch, 4107m(nottoscale).ThiswastheviewfromtheSaasFeeschoolinMürren,photographedbyBen Moore. The image of Andromeda is from http://commons.wikimedia.org/wiki/File%3A Andromeda_Galaxy_(with_h-alpha).jpg, by Adam Evans [CC-BY-2.0 (http://creativecommons. org/licenses/by/2.0)],viaWikimediaCommonsfromWikimediaCommons. ISSN 1861-7980 ISSN 1861-8227 (electronic) ISBN 978-3-642-41719-1 ISBN 978-3-642-41720-7 (eBook) DOI 10.1007/978-3-642-41720-7 Springer Heidelberg NewYork Dordrecht London LibraryofCongressControlNumber:2014931389 (cid:2)Springer-VerlagBerlinHeidelberg2014 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purposeofbeingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthe work. 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Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface Understanding the origin of galaxies is one of the major research goals of astro- physicists. Our own Milky Way and its neighbouring galaxies provide the ideal laboratorytofacilitateadeeperunderstandingofhowgalaxiesform.Wecanlook in detail at the different components of our Milky Way and try to reconstruct events in the distant past through present-day clues—in essence we are carrying out archaeology on a galactic scale. Our Galaxy resides in The Local Group, an overdense region out to about ten megaparsecs from the Milky Way. This region includes Andromeda (M31) a similar galaxy as our own, as well as a few dozen smaller galaxies and satellites. This environment is typical of most galaxies in our Universe. In a few billion years,theLocalGroupwillhaveevolvedintoasinglelargeellipticalgalaxyasits most massive members merge together. TheoriginoftheGalaxyandLocalGroupisplacedwithintheframeworkofthe standardLCDMbigbangcosmology.TheMilkyWayanditssatellitescontinueto provide tests and constraints on theories of galaxy formation and on the standard cosmologicalmodel—namelyahierarchicaluniverseinwhichstructureformation is driven by an underlying dominant component of cold dark matter. The following chapters contain a broad and detailed overview of our current understandingoftheorigin ofourMilky Way Galaxy andthe LocalGroup.They representthecurrentstateoftheartintheexcitingtopicofNearFieldCosmology. Theseup-to-datereviewsarebasedonlecturesgivenattheinspiring37thSaas Fee School held in Muerren, Switzerland. Muerren is a car-free mountain village high above the spectacular Lauterbrunnen valley in the Bernese Oberland. The schoolwasentitled‘‘TheOriginoftheGalaxyandLocalGroup’’anditwasattended by over 100 young astronomy students. The School was organised by Prof. Ben Moore(UniversityofZurich)andProf.EvaGrebel(UniversityofHeidelberg)and thelecturesweregivenbyworldexpertsonthesetopics:Prof.JossBland-Hawthorn (Sydney Institute for Astronomy), Prof. Kenneth Freeman (Mount Stromlo Observatory)andProf.FrancescaMatteucci(TriesteUniversity). Zu¨rich, June 2013 Ben Moore v TheOriginOfTheGalaxyandLocalGroup 37thSaasFeeAdvancedCourse Contents 1 Near Field Cosmology: The Origin of the Galaxy and the Local Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Joss Bland-Hawthorn and Kenneth Freeman 1.1 Prologue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Far Field Cosmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2.1 The Cosmic Microwave Background . . . . . . . . . . . . . 4 1.2.2 The First Stars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.3 The First Black Holes. . . . . . . . . . . . . . . . . . . . . . . . 10 1.2.4 The First Dark Haloes . . . . . . . . . . . . . . . . . . . . . . . 12 1.2.5 Reionization and the First Galaxies . . . . . . . . . . . . . . 15 1.3 Lessons from Galaxy Redshift Surveys. . . . . . . . . . . . . . . . . . 16 1.3.1 Evolution and Environment. . . . . . . . . . . . . . . . . . . . 19 1.3.2 Accretion and Feedback . . . . . . . . . . . . . . . . . . . . . . 20 1.3.3 Baryon Inventory and Metal Enrichment. . . . . . . . . . . 22 1.3.4 Chemical Evolution in Galaxies. . . . . . . . . . . . . . . . . 25 1.3.5 Milky Way and Local Group Analogues in the Real Universe. . . . . . . . . . . . . . . . . . . . . . . . . 25 1.3.6 Milky Way and Local Group Analogues in Simulated Universes. . . . . . . . . . . . . . . . . . . . . . . 26 1.4 Gas Accretion onto Galaxies. . . . . . . . . . . . . . . . . . . . . . . . . 27 1.4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1.4.2 Earliest Epoch of Gas Accretion . . . . . . . . . . . . . . . . 28 1.4.3 Early Ideas on Galaxy Accretion. . . . . . . . . . . . . . . . 30 1.4.4 Accretion Shocks. . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1.4.5 Cooling Flows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.4.6 Cold Flows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 1.4.7 Warm Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1.4.8 Accretion via Major and Minor Mergers. . . . . . . . . . . 38 1.4.9 Accretion of High Velocity Clouds . . . . . . . . . . . . . . 39 1.5 Near Field Cosmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 1.5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 1.5.2 A Working Model of How the Galaxy Formed . . . . . . 47 vii viii Contents 1.5.3 Timescales and Fossils. . . . . . . . . . . . . . . . . . . . . . . 49 1.5.4 Stellar Age Dating. . . . . . . . . . . . . . . . . . . . . . . . . . 51 1.5.5 Goals of Near Field Cosmology. . . . . . . . . . . . . . . . . 54 1.6 Structure of the Galaxy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.6.1 The Bulge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.6.2 The Disk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 1.6.3 The Stellar Halo . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 1.6.4 The Dark Halo . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 1.7 Signatures of Galaxy Formation. . . . . . . . . . . . . . . . . . . . . . . 63 1.7.1 Zero Order Signatures: Information Preserved Since Dark Matter Virialized . . . . . . . . . . . . . . . . . . . . . . . 63 1.7.2 First Order Signatures: Information Preserved Since the Main Epoch of Baryon Dissipation. . . . . . . . . . . . 68 1.7.3 Second Order Signatures: Major Processes Involved in Subsequent Evolution . . . . . . . . . . . . . . . 74 1.8 Reconstructing the Past Through Chemical Tagging. . . . . . . . . 86 1.8.1 Unravelling a Dissipative Process . . . . . . . . . . . . . . . 86 1.8.2 How Many Star Clusters?. . . . . . . . . . . . . . . . . . . . . 88 1.8.3 Cluster Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . 89 1.8.4 Chemical Homogeneity. . . . . . . . . . . . . . . . . . . . . . . 90 1.8.5 Unique Chemical Signatures . . . . . . . . . . . . . . . . . . . 92 1.8.6 Primary Requirements of Chemical Tagging. . . . . . . . 92 1.8.7 Candidates for Chemical Tagging . . . . . . . . . . . . . . . 97 1.8.8 Short-Term Goal: Size and Structure in a Multi-Dimensional C-Space . . . . . . . . . . . . . . . . 100 1.8.9 Long-Term Goal: Reconstructing Ancient Star Groups from Unique Chemical Signatures . . . . . . . . . 101 1.9 Epilogue: Challenges for the Future. . . . . . . . . . . . . . . . . . . . 104 1.9.1 The Limitations of Near Field Cosmology: Are We Really Putting KCDM to the Test? . . . . . . . . 104 1.9.2 Future Surveys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Appendix A: The Discovery of Dark Matter in Galaxies . . . . . . . . . . 109 Appendix B: Stellar Data: Sources and Techniques. . . . . . . . . . . . . . 112 B.1 Data Needed for Galactic Archaeology. . . . . . . . . . . . 112 B.2 Sources of Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 B.3 Sources of Models. . . . . . . . . . . . . . . . . . . . . . . . . . 125 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 2 Chemical Evolution of the Milky Way and Its Satellites . . . . . . . . 145 Francesca Matteucci 2.1 How to Model Galactic Chemical Evolution. . . . . . . . . . . . . . 145 2.1.1 The Initial Conditions. . . . . . . . . . . . . . . . . . . . . . . . 146 Contents ix 2.1.2 Birthrate Function . . . . . . . . . . . . . . . . . . . . . . . . . . 146 2.1.3 Stellar Yields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 2.1.4 Gas Flows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 2.2 Basic Equations for Chemical Evolution. . . . . . . . . . . . . . . . . 158 2.2.1 Yields per Stellar Generation. . . . . . . . . . . . . . . . . . . 158 2.2.2 Analytical Models . . . . . . . . . . . . . . . . . . . . . . . . . . 159 2.2.3 Detailed Numerical Models. . . . . . . . . . . . . . . . . . . . 162 2.3 The Milky Way. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 2.3.1 The Formation of the Milky Way . . . . . . . . . . . . . . . 164 2.3.2 The Two-Infall Model . . . . . . . . . . . . . . . . . . . . . . . 166 2.3.3 Detailed Recipes for the Two-Infall Model. . . . . . . . . 167 2.3.4 The Chemical Enrichment History of the Solar Vicinity. . . . . . . . . . . . . . . . . . . . . . . . . 170 2.3.5 The Galactic Disk . . . . . . . . . . . . . . . . . . . . . . . . . . 181 2.3.6 The Galactic Bulge . . . . . . . . . . . . . . . . . . . . . . . . . 186 2.4 What We Have Learned About the Milky Way. . . . . . . . . . . . 194 2.5 The Time-Delay Model and the Hubble Sequence. . . . . . . . . . 194 2.5.1 Star Formation and Hubble Sequence. . . . . . . . . . . . . 195 2.6 Dwarf Spheroidals of the Local Group. . . . . . . . . . . . . . . . . . 198 2.6.1 How do dSphs Form?. . . . . . . . . . . . . . . . . . . . . . . . 198 2.6.2 Observations of dSphs . . . . . . . . . . . . . . . . . . . . . . . 200 2.6.3 Chemical Evolution of dSphs . . . . . . . . . . . . . . . . . . 200 2.6.4 What Have we Learned About dSphs?. . . . . . . . . . . . 208 2.7 Ultra-Faint Dwarfs in the Local Group. . . . . . . . . . . . . . . . . . 212 2.8 Other Spirals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 2.8.1 Chemical Models for External Spirals . . . . . . . . . . . . 215 2.9 Cosmic Chemical Evolution . . . . . . . . . . . . . . . . . . . . . . . . . 217 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Chapter 1 Near Field Cosmology: The Origin of the Galaxy and the Local Group JossBland-HawthornandKennethFreeman The Galaxy has built up through a process of accretion and merging over billions of years which continues to this day. Astronomers are now embarking on a new eraofmassivestellarsurveysoverthecomingdecade.Thesecampaignswillderive three-dimensionalspacemotionsandheavyelementabundancesformillionsofstars throughouttheGalaxyanditsneighbours.Thenewobservationswillrevealsigna- turesoftheformationandearlyevolutionoftheLocalGroup;thisiswhatwemean by‘nearfieldcosmology.’Wesetthisnewcourseofstudywithinthecontextoffossil signaturesfromgalaxysurveysandthehighredshiftuniverse.Wediscussthecom- plexrelationshipbetweenbaryonsanddarkmatterovercosmictime,andintroduce asyntheticframeworkthatwillallowbothnumericalsimulationsandtheimpending datadelugetobecompared.Wealsoincluderelevantsourcematerialsfortheyoung near-fieldcosmologistandsomehistoricalperspectives. 1.1 Prologue Inanearlierreview,weoutlinedtheconceptofnearfieldcosmologytoemphasize thefactthatthereareancientsignaturesallaroundustodayprovidingevidenceof theformation processes that ledtotheGalaxy and the Local Group (Freeman and Bland-Hawthorn2002).Weseeancientstarsaroundusintheoldthindisk,thethick disk,thestellarhalo,theinnerbulge,andinsatellitedwarfgalaxies.Abouthalfof all stars in the Galaxy today formed before a redshift z ∼ 1. The Hubble Space Telescope(HST)probestheseearlyformationepochsdirectlyduringatimewhen B J.Bland-Hawthorn( ) SydneyInstituteforAstronomy,UniversityofSydney,Sydney,NSW2006,Australia e-mail:[email protected] K.Freeman MountStromloObservatory,AustraliaNationalUniversity,WestonCreek,ACT2611,Australia e-mail:[email protected] B.Moore(ed.),TheOriginoftheGalaxyandLocalGroup, 1 Saas-FeeAdvancedCourse37,DOI:10.1007/978-3-642-41720-7_1, ©Springer-VerlagBerlinHeidelberg2014
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