1976MNRAS.177..357E 12 Mon. Not.R.astr.Soc.(1976)177,357-375. very highvaluefordeterminingthemassof system. around theGalaxyinLocalGroup)?Inthis respectwehavetwoalternatives. mass oftheHypergalaxy(thesubcondensation of galaxiesandintergalacticmatter Hypergalaxy andpasstheGalaxyathyperbolic velocities,thenthekinematicsof only inconnectionwiththethirdquestion—can HVCsbeusedtoestimatethe (1970), Mathewson,Cleary&Murray(1974a), Mathewson(1976),Einastoetal. members ofourHypergalaxy. WeusethekinematicsofHVCsaswell asother If HVCs,includingtheMagellanicStream,are notpermanentmembersofthe (1975) andothers.Weshallconsiderthesehypotheses inthefollowingsections cerning thefirsttwoquestions.ThesehypotheseshavebeendiscussedbyOort come totheconclusion thatthetotalmassofourHypergalaxyis (i-2±o*5)x independent datainorder togetamassestimateoftheHypergalaxy. Wehave HVCs arepermanentmembersofourHypergalaxy, thentheirkinematicsisof HVCs isoflittlesignificanceforsolvingthethird problem.Onthecontrary,if of HVCstellusanythingaboutthemassdistributionaroundGalaxy? our GalaxyormembersoftheLocalGroupasawhole?;(c)doeskinematics (HVCs) aroundourGalaxyraisesanumberofquestions,forexample: ioM. A similar conclusion,based onsimilararguments butusingadifferent 0 © Royal Astronomical Society • Provided by theNASA Data System A varietyofdifferenthypotheseshavebeenproposedbyvariousauthorscon- As weshallseelater,there aregoodreasonstobelievethatHVCspermanent (a) WhatistheoriginofHVCs?;(b)areHVCspermanentcompanions The discoveryoftheMagellanicStreamandotherhighvelocityclouds ,12 members ofthesystemcompanionsourGalaxy.Usingkinematics The kinematicsoftheMagellanicStreamandotherhighvelocityclouds Hypergalaxy (thesubcondensationofgalaxiesandintergalacticmatteraround is investigated.Argumentsarepresentedtoshowthattheypermanent the GalaxyinLocalGroup)isestimated:Mtot=(i2±o*5)xioM. distribution ofthecompanionsGalaxy,virialtheoremmassour of highvelocitycloudsandotherobjectsaswellthespatial sistent withthehypothesisthatcloudsofStreamaremovingaround (change ofvelocities,densitiesandangularsizealongtheStream)arecon- Galaxy alongellipticalorbits(Rmin#14kpc,Rmax#100kpc). It isshownthatessentialobservedpropertiesoftheMagellanicStream 0 Astrophysical ,202444,,Toravere,,USSR Jaan Einasto,UrmasHand,MihkelJoeveerandAntsKaasik AND THEMASSOFOURHYPERGALAXY (Received 1976May24;inoriginalformFebruary2) THE MAGELLANICSTREAM I. INTRODUCTION SUMMARY 1976MNRAS.177..357E 358 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System J. Einastoetal. o O ÍI3 Vol. 177 1976MNRAS.177..357E -1 -1 21/ 2 -1 -1 -1 method, hasbeenreachedbyLynden-Bell(1975,privatecommunicationand No. a,1976TheMagellanicStreamandHypergalaxymass359 HVCs, includingthecloudsbelongingtoMagellanicStream.Theresultinglist & Kraus1970;WannierWrixon1972)wehavecollectedavailabledataon using theequation respect tothelocalstandardofrestFlsrwerecorrectedforgalacticrotation, contains 740entries.Inmanycloudcomplexesvelocityhasbeenmeasuredat different points,allthesepointshavebeenlistedseparately.Radialvelocitieswith 1976). constants (Einasto,Joeveer&Kaasik1976).Thesamevaluehasbeenusedalsoby galactic centrethevalueFo=225kmsaccordingtoournewsystemof system individualcloudsoftheStreamarelocatedclosetoequator. coordinate systemhasgalacticcoordinates/=ii°,è—3°*5.Inthis In thisformulawehaveadoptedfortherotationalvelocityofSunaround large surfacedensityhavebeenplotted.ThecloudsbelongingtotheMagellanic (0, À)coordinatesystem.AplotofHVCsFgsr^angulardistancedalongthe coordinates (/,b)weshalluseanewcoordinatesystem(0,À).Thepoleofthe Mathewson etal.(1974b). therefore, difficulttoobtainanunbiasedestimateofthevelocitydispersion tion. AsseenfromFig.3,atlargevelocities(Fgsr>iookms)thenormallaw is showninalogarithmicscale(dots);thefulllinerepresentsnormaldistribu- from Fig.3.Inthisdiagramthenumberofcloudsatsucce