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Astrophysics and Space Science Library 420 Heidi Jo Newberg Jeffrey L. Carlin Editors Tidal Streams in the Local Group and Beyond Observations and Implications Astrophysics and Space Science Library Volume 420 Editorial Board Chairman W.B. Burton, National Radio Astronomy Observatory, Charlottesville, VA, USA ([email protected]);UniversityofLeiden,TheNetherlands ([email protected]) F.Bertola,UniversityofPadua,Italy C.J.Cesarsky,CommissionforAtomicEnergy,Saclay,France P.Ehrenfreund,LeidenUniversity,TheNetherlands O.Engvold,UniversityofOslo,Norway A.Heck,StrasbourgAstronomicalObservatory,France E.P.J.VanDenHeuvel,UniversityofAmsterdam,TheNetherlands V.M.Kaspi,McGillUniversity,Montreal,Canada J.M.E.Kuijpers,UniversityofNijmegen,TheNetherlands H.VanDerLaan,UniversityofUtrecht,TheNetherlands P.G.Murdin,InstituteofAstronomy,Cambridge,UK B.V.Somov,AstronomicalInstitute,MoscowStateUniversity,Russia R.A.Sunyaev,SpaceResearchInstitute,Moscow,Russia Moreinformationaboutthisseriesathttp://www.springer.com/series/5664 Heidi Jo Newberg • Jeffrey L. Carlin Editors Tidal Streams in the Local Group and Beyond Observations and Implications 123 Editors HeidiJoNewberg JeffreyL.Carlin DepartmentofPhysics,AppliedPhysics DepartmentofPhysics,AppliedPhysics andAstronomy andAstronomy RensselaerPolytechnicInstitute RensselaerPolytechnicInstitute Troy,NY,USA Troy,NY,USA ISSN0067-0057 ISSN2214-7985 (electronic) AstrophysicsandSpaceScienceLibrary ISBN978-3-319-19335-9 ISBN978-3-319-19336-6 (eBook) DOI10.1007/978-3-319-19336-6 LibraryofCongressControlNumber:2015956760 SpringerChamHeidelbergNewYorkDordrechtLondon ©SpringerInternationalPublishingSwitzerland2016 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublication doesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. Thepublisher,theauthorsandtheeditorsaresafetoassumethattheadviceandinformationinthisbook arebelievedtobetrueandaccurateatthedateofpublication.Neitherthepublishernortheauthorsor theeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinorforany errorsoromissionsthatmayhavebeenmade. Coverillustration:The“FieldofStreams”(afterBelokurov,V.,Zucker,D.B.,Evans,N.W.etal.,2006, ApJL,642,L137asreproducedwithmorerecentdatabyMatthewNewby)showsthedensityofmain sequenceturnoffstarsinthenorthGalacticcap,colorcodedbydistance.Blueiscloserandredisfarther away.ThestarswereselectedfromtheSloanDigitalSkySurveyDataRelease10.Thisbeautifulimage showsthattheouterstellarhaloisdominatedbyseverallarge“streams”ofstars.Thesestarswereripped fromtheirprogenitordwarfgalaxiesbytidalforcesintheMilkyWay.TheimageisplottedinEquatorial coordinateswithdeclination-correctedbinsof0.25degree(cid:2)0.25degreeeach. Printedonacid-freepaper Springer International Publishing AG Switzerland is part of Springer Science+Business Media (www.springer.com) Preface This book introduces the field of tidal streams, charts the major discoveries that broughtus to our current understanding, and gives the reader a sense of the field as we knowit. Because this field is quite young,the researcherswho made major contributions are still active in the field. I am quite fortunate and grateful that many of these wonderfulpeople agreed to contribute chapters to this book. Their expertiseandwillingnesstoshareitinthiswaywereessentialtothebook’ssuccess. Iwouldparticularlyliketothankmyco-editorJeffCarlinforsteppingintobridge any scientific or technical gaps that arose. In addition to having made important contributions to the field of tidal streams, he has an incredible ability to spot grammar and spelling errors, which was put to great use as he copy edited every singlechapterofthisbook.Iamquitehappywiththeresult. Therearesomenotablescientistsinthisfieldwhowerenotavailableorwerenot askedtowritechapters,andbecauseofthisIamsurethatthereiswisdomthathas notbeenpasseddowninthisvolume.Ihopethatwehaveatleastdoneareasonable jobofcoveringthemajorresultspresentedintheirpapers.Iapologizeinadvanceto thosewhoseworkwasmissedorwasnotasfullyrepresentedasitcouldhavebeen. OneofthethingsIhavepersonallylearnedinwritingandeditingthisbookisthat each of us watches the field evolve from our own vantagepoint. We do notknow everythingthat has been discovered, or we learn about results in differentorders, and we are not all influenced by the same results in the same way. In editing the chapters of this book, my primary intent was to improve clarity and style and to coverasmuchmaterialaspossiblewithoutduplication.I thinkitisimportantthat ineachchapterthehistoricalviewpointisthatoftheauthorsofthatchapteratthe timethechapterwaswritten. Thisbookcertainlywillnotbethedefinitivebookontidalstreams,inthesense thatdefinitive impliesthe materialpresentedis final, settled, or inarguable.I have personally learned an enormous amount in researching my portion of this book andin editingthe contributionsof others.Our knowledgeof tidalstreams andthe informationthey give us on the quantity and location of dark matter in the Milky Way is still evolving. Keep in mind that writing the book took about 2years, and the chapters of more conscientious writers were finished months ahead of those v vi Preface for whom deadlinesare less important. Some importantfindingspresented in this volumewerediscoveredwhilethechapterswerebeingwritten! I consciously decided not to attempt to make all of the chapters completely consistent.We donotallagreeontheidentityofthetidalstreams.Thereisstellar structure in the plane of the Milky Way that some believe was ripped from dwarf galaxiesastheyfellintoourgalaxy,andothersarejustassureismaterialthrown upfromthedisk.Wedon’tallagreeaboutwhetherallofthematerialintheorbital plane of the Sagittarius dwarf tidal stream was ripped from the Sagittarius dwarf galaxy, or whether it came from multiple infalling dwarf galaxies, or how many timestheSagittariusdwarftidalstreamwrapsaroundtheMilkyWay.Wedon’tall agreethatalloftheobjectsidentifiedastidalstreamsareactuallytidaldebris,and wecertainlydon’tallagreeonthefluffierstructuresofstarsthatwecall“clouds.” Butthe chaptersin thisbookoutlinethe publishedworkofexpertsin the field,as interpretedby expertsin thefield, andwill serveasa reliableguideto ourcurrent bestunderstanding. IhopethisbookwillteachyouasmuchasIhavelearnedineditingit,andthatit willinspireyoutosolvethemanyoutstandingquestionsitdescribes. Troy,NY,USA HeidiJoNewberg August2015 Contents 1 IntroductiontoTidalStreams.............................................. 1 HeidiJoNewberg 1.1 AnOverviewofTidalStreamsandHaloSubstructure................ 1 1.2 TheDiscoveryofTidalStreamsintheMilkyWay.................... 4 1.2.1 DwarfGalaxiesandMovingGroups .......................... 4 1.2.2 HaloSubstructureintheEraofLargeSurveys................ 7 1.3 ObservationalTechniquesforFindingSubstructure .................. 15 1.3.1 StandardCandlesandPhotometricParallax................... 15 1.3.2 MatchedFilterTechniques..................................... 17 1.3.3 StatisticalPhotometricParallax................................ 19 1.4 Co-movingGroupsofStars ............................................ 21 1.5 ChemicalTagging....................................................... 22 1.6 ConstrainingDarkMatter,theFormationoftheMilky Way,andCosmologywithTidalStreams.............................. 23 1.6.1 RapidCollapsevs.HierarchicalMergers...................... 23 1.6.2 ConstrainingDarkMatterwithTidalStreams................. 24 1.7 DiskResponsetoTidalInteractions.................................... 25 1.8 FutureProspects......................................................... 26 References..................................................................... 27 2 TheSagittariusDwarfTidalStream(s).................................... 31 DavidR.LawandStevenR.Majewski 2.1 Introduction ............................................................. 31 2.2 HistoricalRemarksandBasicStructureoftheSagittariusSystem... 32 2.3 StellarPopulationsWithintheSagittariusSystem .................... 37 2.3.1 StellarPopulationsintheSagittariusCore .................... 37 2.3.2 StellarPopulationsintheSagittariusStreams................. 41 2.3.3 ChemicalEvolutionoftheSagittariusSystem................ 42 2.3.4 SagittariusStarClusters........................................ 44 vii viii Contents 2.4 NumericalModelsoftheSagittarius-MilkyWaySystem............. 45 2.4.1 GeneralApproach .............................................. 45 2.4.2 ConstraintsontheShapeoftheGalacticDark MatterHalo ..................................................... 48 2.4.3 ConstrainingtheMassoftheGalacticDisk................... 51 2.5 Mass,LuminosityandMass-to-LightRatioofSagittarius............ 52 2.6 OutstandingIssuesRegardingtheDetailedStructure oftheSagittariusSystem ............................................... 54 2.6.1 ABifurcatedStreamDensityProfile........................... 54 2.6.2 Multiply-WrappedSagittariusStreams........................ 56 References..................................................................... 59 3 TheMonocerosRing,andOtherSubstructureNearthe GalacticPlane ................................................................ 63 BrianYannyandHeidiJoNewberg 3.1 TheMonocerosRingIsDiscoveredandNamed ...................... 63 3.2 DraggedInorDredgedUp?TheDebateOvertheOrigin oftheMonocerosRing.................................................. 67 3.3 PropertiesoftheMonocerosStructure................................. 71 3.4 TheCanisMajorDwarfGalaxyControversy.......................... 77 3.5 TheTriangulum-Andromeda,andOtherLowLatitude, Stream-LikeSubstructuresNeartheAnticenter....................... 79 3.6 ExplainingtheMonocerosRingandOtherLowLatitude SubstructureswithaCorrugatedMilkyWayDisk .................... 80 3.7 FutureProspects......................................................... 84 References..................................................................... 84 4 StellarStreamsandCloudsintheGalacticHalo......................... 87 CarlJ.GrillmairandJeffreyL.Carlin 4.1 ObservationalTechniques .............................................. 87 4.2 CurrentlyKnownStellarDebrisStreamsandClouds intheGalacticHalo..................................................... 89 4.2.1 StreamswithKnownorLikelyGlobularCluster Progenitors...................................................... 98 4.2.2 StreamswithPresumedDwarfGalaxyProgenitors........... 101 4.2.3 CloudsandOtherDiffuseStellarStructures .................. 103 4.3 FutureDiscoveries...................................................... 108 References..................................................................... 110 5 KinematicallyDetectedHaloStreams..................................... 113 MartinC.Smith 5.1 IntroductiontoKinematicStreams..................................... 113 5.2 LocalKinematicStreams............................................... 115 5.2.1 TheHelmiStream .............................................. 115 5.2.2 OtherEarlyDiscoveries........................................ 118 Contents ix 5.2.3 StreamsintheGeneva-CopenhagenSurvey................... 119 5.2.4 TheModernEra................................................. 123 5.3 DistantHaloStreams ................................................... 130 5.4 FutureProspects......................................................... 133 References..................................................................... 136 6 OriginsandInterpretationofTidalDebris ............................... 141 KathrynV.Johnston 6.1 Introduction ............................................................. 141 6.2 IllustrativeN-BodySimulations........................................ 142 6.3 BasicPrinciplesofDebrisFormationandEvolution.................. 143 6.3.1 DebrisSpreading:Phase-Mixing............................... 143 6.3.2 OrbitalPropertiesofTidalDebris.............................. 149 6.3.3 Application:ModelsofStreams ............................... 151 6.4 Morphologiesof IndividualDebris Structures in ObservableCo-ordinates................................................ 153 6.4.1 YoungDebris ................................................... 154 6.4.2 FullyPhase-MixedDebris...................................... 155 6.5 Debris in a CosmologicalContext: Modeling and InterpretingPropertiesofStellarHalos................................ 156 6.5.1 CosmologicalSimulationsofStellarHaloFormation ........ 157 6.5.2 GeneralResultsofCosmologicalAccretionModels.......... 158 6.5.3 ImplicationsandApplications ................................. 162 6.6 SummaryofStatusandProspects...................................... 165 References..................................................................... 166 7 TidalDebrisasaDarkMatterProbe...................................... 169 KathrynV.JohnstonandRaymondG.Carlberg 7.1 Introduction ............................................................. 169 7.2 UsingTidalDebristoProbetheGlobalPotential..................... 171 7.2.1 PredictiveModels............................................... 173 7.2.2 FundamentalMethods.......................................... 175 7.2.3 Summary:StatusandProspects................................ 176 7.3 UsingTidalDebristoProbeDarkMatterSubstructure............... 178 7.3.1 CosmologicalContext.......................................... 178 7.3.2 DarkMatterEncounterswithThinStellarStreams........... 180 7.3.3 CurrentObservationsandFutureProspects................... 187 References..................................................................... 188 8 SubstructureandTidalStreamsintheAndromedaGalaxy anditsSatellites.............................................................. 191 AnnetteM.N.FergusonandA.D.Mackey 8.1 Introduction ............................................................. 191 8.2 HistoricalStudies ....................................................... 193 8.3 Wide-FieldMappingSurveysofM31 ................................. 194 8.4 MajorTidalFeaturesintheHaloofM31.............................. 196