Tidal Streams in the Local Group and Beyond: Observations and Implications

256 Pages·2016·9.767 MB·English

by  Heidi Jo Newberg, Jeffrey L. Carlin (eds.)

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
([e-mail]);UniversityofLeiden,TheNetherlands
([e-mail])
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