198 3MNRAS.205.1191M _1 1 -1 ultraviolet spectrafromtheInternationalUltraviolet Explorer{IUE)takeninthedirections our ownGalaxyandtheMagellanicClouds.Savage &deBoer(1981)haveexaminedfar- to thelocalstandardofrest (LSR).Gondhalekaretal(1980)havedetected UV components of starsintheLargeMagellanicCloud(LMC),and notethattheweakerlow-ion-stagelines oxygen theyfoundatthese velocitiesimpliesthatneutralhydrogenshould alsobepresent. at +54and134kms in twoLMCstars;Songaila(1981)foundvisibleabsorption linesat show acomponentstructurewithstrongfeatures near+60and+130kms"withrespect In thepastfewyearsevidencehasbeenmounting for thepresenceofgaseoushaloesaround However, extrapolatingthe solarabundanceratioswouldgiveanHicolumn densityof ~+65 and+133kms in fourLMCstars.AsSavage&deBoerpoint out, theneutral 1 Introduction © Royal Astronomical Society • Provided by theNASA Astrophysics Data System _1 1 R. X.McGeeandLynetteM.NewtonDivisionofRadiophysics, Donald C.MortonAnglo-AustralianObservatory,POBox296,Epping, CSIRO, POBox76,Epping,NSW2121,Australia Neutral hydrogeninthehaloesofGalaxyand the LMC Mon. Not.R.astr.Soc.(1983)205,1191-1205 NSW 2121,Australia Received 1983April26;inoriginalform1982November19 intensity HiexistsinthreeregionsataverageLSRradialvelocitiesof—40, halo aroundtheLargeMagellanicCloud. interpreted ascomponentsofthegalactichaloatconsiderabledistances at heliocentricvelocitiesof+197and+360kmspossiblyindicateasimilar neutral elementsinthegalactichalo.Theobservationsshowthatverylow- telescope hasledtothedetectionofHicounterpartionizedand Summary. Anewlow-noise21-cmlinereceiverinstalledontheParkes64-m + 59andISlkms"which,ifthehaloiscorotatingwithdisc,canbe tions withtheInternationalUltravioletExplorerandpresentHiobserva- below thegalacticplane.Twoadditionalgroupsoflow-intensityHifeatures tion showthatOiinthehaloisdepletedbyafactorbetween2and10 with thegalacticdiscandMagellanicClouds. Thus Caappearstofollow compared tosolarabundance.Oftheelementswhichshouldbedominantin the typicalpatternofbeingdepletedlessinhalo thaninthespiralarms. factors of4to3000,withthegreatervaluesoccurringatvelocitiesassociated solar abundance.Ground-baseddataonCanshowthatitisdepletedby H iregionsA1andSiaredepletedbyafactorof<2Feisclosetothe Comparison ofthecolumndensitiesobtainedbyultravioletobserva- 198 3MNRAS.205.1191M 1 182 1 1 = 1 _1 1 1 believe indicatesahaloaroundtheLMC. mediate andhigh-velocitygascomponents,thatagalactichaloexiststowardstheMagellanic corroborate theconclusionsofSavage&deBoer(1981),especiallywithrespecttointer- reasonable observingtime.WereporthereaseriesofHiobservationswhichstrongly radio telescopehasmadeitpossibleforsignalsfromsuchtenuousHitobedetectedina detected inthesedirections.Alow-noise21-cmreceivernowinstalledontheParkes64-m were inthedirectionsofninestarsMagellanicCloudsreportedbySavage&de means ofthebeamwidthsathalfpowerwereeach14.9±0.1arcmin.Thespectrometerwas inputs totwoseparatechannels.ThefirststagesofeachchannelareFETamplifiers, The 21-cmreceiverhasa1HEhybrid-modefeedhornwithorthogonalprobeswhichactas Clouds. Inadditionwehavefoundgasat+197and+360kms"(heliocentric)which 46 K.Intensitycalibrationsandtelescopebeam-sizemeasurementsweremadeonthesources cryogenically cooledto20K.Thesystemtemperaturesoncoldskywerefoundbe44and ~ 4x10atomcm"—atleastanorderofmagnitudebelowtheHisignallevelspreviously equivalent radialvelocitywidthsof0.82,1.65,4.1and8.2kms"perchannel. and antennatemperaturewasS/T=1.62JyK';thebeamefficiencyT70.8.The Hydra A(S^i=43.5Jy)and1934-63(S2115.4Jy).Therelationbetweenfluxdensity the 1024-channeldigitalcorrelatorarrangedinconfigurationstogivebandwidthsof 2 Equipmentandobservations 1192 R.X.McGee,L.M.NewtonandD.C.Morton Boer (1981).Thetwonarrowbandwidthswereused(beinglaterHanning-smoothedto AB equivalent widthsof1.6and3.3kms")withvelocityranges—100to+lOOkms" unsuccessful attempttodetectH1absorptionofextragalacticsourcesbytheMagellanic reduced toapeak-to-peakvalueof0.03Kinmostcases. spectra, each‘onandoff’integratedfor15min,wereaverageduntilthenoiselevelwas frequency range2.5MHzbelowtheobservingband.Sufficientnumbersofdifference — 20to+400kmsrespectively.Referencespectrawereobtainedbyswitchinga objects intheLMContwooccasions(forJ.Meaburn,UniversityofManchester),andan observations weremadeat8.2kms"perchannel using anotherquadrantofthecorrelator. tions arebeingmade.Althoughwehavenothadthe opportunityofmakingobservationsat features discussed.Seventy-eightprofileshavebeen analysedintheregionofskycontaining 4.1 kms”perchannelwasusedwithanoverallrangeof-450kms'.Simultaneous Stream (forM.V.Pension,RoyalGreenwichObservatory).Inthesecasesthebandwidthof the SMC,partofMagellanicStreamandLMC —fromgalacticlongitudes/=302°to set byafactorof2,buttheywerestillmorethan adequatetodetectthelow-intensityHi tion bystrayradiation,i.e.21-cmlineradiationentering thereceiverthroughsidelobes problem. tion, ourcalculationslead ustobelievethat,apartfromcontributionsthe localprofile, of thetelescopefromstrongH1sourcesthatmay be elsewhereintheskywhenobserva- 277° andatgalacticlatitudesbetweenb=—30° —58°,wellclearofthegalacticplane. the contaminationof featureswepresenthereisnotserious.Since cannot ruleout different timesthroughout theyearwithaviewofrecognizingandeliminating strayradia- Less integrationtimewasavailableandthenoiselevels achievedwereworsethaninthefirst the possibilityofcontamination, wehaverequestedtelescopetimeto investigate this © Royal Astronomical Society • Provided by theNASA Astrophysics Data System The observationsweremadeinfourseparatesessionsonthetelescope.Infirstthey The otherthreesetsofdatawereobtainedincidentallyduringobservationsparticular In reportingtheselow-level21-cmlineswehaveconsidered thepossibilityofcontamina- 198 3MNRAS.205.1191M 1 Wideband (10MHz,equivalentto2100kms")observationstakeninconjunctionwiththe Figure 1.RepresentativeHI(21 cm)profilesfromdirectionstowards:SMC(a);Magellanic Stream(e),(f); observations discussedhereenabledustoestablishandcheckaccuratebaseHnesforthe LMC (b),(c),(d), (g),(h).Low-intensityfeatures onlyareshown,withGaussian curvessuperimposed. 3 Thedata profiles. IndisplayingthedatainFig.1wehavetruncatedstrongHisignalsfrom LU X. © Royal Astronomical Society • Provided by theNASA Astrophysics Data System lSR Heliocentric _1 Radial Velocity(kms) Hydrogen intheGalaxyandLMC1193 198 3MNRAS.205.1191M HD 5980 Table 1.Radialvelocities,halfwidthsandcolumndensitiesofthelowintensity21cmH-line components. Sk 108 Sk 80 Source name 1194 R.X.McGee,L.M.NewtonandD.C.Morton Fairall 9012151-590357295.1-57.8 MS 1.2 MS 1.3 MS 1.0 MS 1.4 MS 5.4 MS 1.1 MS 5.3 MS 5.0 MS 5.2 MS 5.1 MS 6.0 MS 2.4 MS MS MS 6.1 MS 6.4 MS MS MS 6.3 MS 6.2 MS 7.0 MS 7.2 MS 7.4 MS 7.3 MS 8.0 MS 8.2 MS 8.4 MS 7.1 MS 8.1 MS 3.3 MS 8.3 MS 9.0 MS 9.2 MS 9.4 MS 3.1 MS 3.0 MS 3.2 MS 3.4 MS 4.2 MS 4.4 MS 9.1 MS 9.3 MS 4.1 MS 4.3 MS 4.0 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System 2.0 2.2 CD 2.1 2.3 01 48-722245 00 5752 00 5746 01 2545 01 2545 01 2338 01 2754 01 2545 01 3041 01 2835 01 3041 01 3249 01 3041 02 3051 02 2319 02 2320 02 2320 02 2015 02 3325 02 3050 02 3050 02 2817 02 2623 02 4145 02 4730 02 4442 02 4443 02 4442 02 5116 02 4844 02 5117 02 5117 02 5117 02 5227 02 5227 02 4922 02 5350 03 1545 03 1300 02 5531 02 5227 03 5526 03 5253 03 1828-6832285.2 -43.3 03 1544 03 1545 03 5800 03 5525 03 5526 R.A. Dec. Position (1950) (2) 72 2600 72 2606 61 3205 61 3205 61 3205 61 4704 61 1704 61 4705 62 0206 62 0203 62 0205 62 1704 66 39 69 2032 66 39 66 54 66 39 66 24 69 2032 69 0533 69 2033 71 1339 70 5840 71 1340 69 3532 71 1339 71 2839 67 45 67 30 67 45 67 00 67 4527 69 45 68 4729 68 3226 68 1729 68 3229 66 3912 66 5412 66 5412 67 0912 66 5412 71 0149 71 1649 71 1648 71 3149 71 1649 27 26 27 27 27 29 27 27 27 28 302.1 301.6 302.1 295.3 295.7 294.9 295.4 295.2 294.4 295.0 294.7 294.6 292.8 292.5 293.0 294.2 288 288 292.4 292.6 288 288 288.9 289.4 288.0 289.3 289.1 287.3 288.8 287.0 286.8 286.3 290.3 286.7 288.8 290.2 290.0 289.8 285.2 285.7 289.8 285.8 285.5 280.3 280.5 280.9 280.6 280.8 coordinates i b Galactic (3) •47.5 •47.7 45.1 45.0 44.9 -43.2 -43.5 •43.7 ■43.7 ■42.7 ■42.7 ■42.9 ■43.1 ■43.0 •45.5 •44.1 55.6 55.4 55.2 55.1 55.3 54.9 54.7 54.7 44.4 44.4 47.9 44.1 44.0 44.2 54.6 54.4 47.9 45.0 47.6 44.7 44.8 45.0 45.8 44.6 45.9 46.2 45.7 41.7 41.3 41.4 41.5 41.6 Rial 0.82 -100,+100 0.82 -100,+100 0.82 -100,+100 8.2 width velocity Band- f 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 4.12 1 (km s') -150,+300 (4) ■70 ,+400 ■70,+4 ■70,+4 •70 ,+400 •70 ,+400 70 ,+400 70 ,+400 70,+400 70 ,+400 70,+400 70,+400 70,+400 range 7-0, +400 70,+400 70,+400 70,+ 400 70 ,+400 70,+400 70,+400 70,+ 400 70,+400 70,+400 70,+400 70,+400 70,+400 70 ,+400 70,+400 70 ,+400 70, +400 70,+400 70,+400 70,+400 70,+400 70 ,+400 70,+400 70 ,+400 70,+400 70,+400 70,+400 70 ,+400 70,+ 400 70,+400 70,+400 70,+400 70 ,+400 70 ,+400 1 velocity (km s') ® -vLSR -10.9 -10.8 -10.8 -11.6 (5) ■15.0 ■14.9 •15.0 •15.0 •14.9 ■14. ■14.0 •14.1 •14.1 11.7 11.8 11.7 11.8 11.7 11.9 11.8 12.0 11.9 11.9 13.3 12.7 12.7 12.7 12.6 13.4 12.8 13.3 13.4 13.3 13.3 13.3 13.3 13.7 13.4 13.4 13.6 13.5 13.7 13.2 13.7 13.3 13.2 13.3 13.2 13.5 14.0 -2 (cm) noise xlplS 0.2- 0.1 -84,+30 0.2 0.2 RMS ÄN 0.5 0.5 0.5 0.5 0.5 0.6 0.6 (6) 0.6 0.6 0.6 h 0.6 0.5 0.5 0.5 0.5 0.6 0.6 0.6 0.5 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.5 0.6 0.6 0.5 0.5 0.6 -70,+48 0.6 0.6 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1 velocity (km s') 65, + 40 64, + 36 73,+40 -74,+36 -74,+42 -76,+39 -71,+46 ■76,+3 ■64,+ ■76,+ 39 ■75,+4 ■73,+4 •74,+58 •76,+46 ■74,+5 •71,+57 •74,+56 ■74,+50 64,+40 62,+50 74,+40 61, +47 74,+40 72,+58 62, +37 74,+40 61 ,+47 62,+57 65,+62 72,+39 77, +45 74, +4 69, +59 75, +45 73,+47 78, + 79 range 78,+71 73,+57 75,+69 74,+58 Local 74,+47 77,+57 70, +54 78,+50 78,+54 78,+45 78,+56 77,+47 (7)t 198 3MNRAS.205.1191M 1-2 + 0.4 -1.5 -2.7 -6.7 18 -0 - 1 - 1 -0 -1.0 - L.1 -2.0 -5.3 18 -5.8 16 -5.5 18 -6.1 16 -5.1 -5.1 -4.7 -5.9 -4.3 ■1.7 ■0.9 •0.6 ■1.6 (km s“)(cm 5.0 161.5 1.0 1.4 1.5 4.4 4.2 6.3 4.3 4.6 4.1 3.2 3.7 1.4 1.6 1.8 3.8 2.9 5.0 3.8 3.0 2.4 3.2 185.0 1.7 1.3 1.3 1.1 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Local (8)t AV 22 20 22 20 18 18 18 20 24 28 26 26 24 22 22 22 24 20 22 16 18 21 20 22 20 16 18 16 14 1Ö 9 1.5 8 1.6 7 1. X1Q20 4.7 4.6 4.0 2.7 2.4 2.5 2.8 3.2 3.0 3.1 2.6 2.4 2.3 2.4 2.6 3.2 2.6 2.7 2.5 3.4 2.8 2.7 2.8 2.4 2.4 2.4 2.5 3.8 2.3 2.3 2.4 2 . 2.8 2.9 1.9 1.8 1.8 2.2 1.7 1.9 1.8 1.9 1.8 1.8 1.7 1 + 67 + 30 + 69 + 74 + 76 + 80 - 28 -32 -37 -32 + 55 + 39 + 49 + 46 + 37 + 47 + 37 + 48 + 48 + 50 + 58 + 85 + 55 + 85 + 97 + 54 + 45 + 47 + 47 + 48 + 49 + 40 + 49 + 44 + 45 + 43 + 48 + 36 + 52 + 73 + 69 + 70 + 61 + 95 -49 -52 -49 -44 + 68 + 68 + 85 + 54 -52 -61 (km s“) V AV Intermediate 24 32 22 19 30 28 23 16 15 19 35 33 40 27 21 22 35 37 22 20 26 22 30 20 18 35 26 25 31 27 26 25 25 23 20 31 22 25 15 25 23 (9)*1- 25 18 15 23 26 12 12 20 20 16 22 22 25 A A A A A A A A A -2 xiq18 16.4 11.8 11.2 13.1 (cm) 9.0 6.1 8.8 3.2 3.5 1.4 4.3 5.1 4.8 4.0 4.6 4.4 3.9 3.6 3.8 4.1 4.4 4.0 3.6 3.6 3.6 0 3 3 3.4 3.3 1 2 2.5 1.9 5.4 2.5 2.0 3.3 2.2 3.8 5.0 2.9 2.9 2.0 1.2 1.6 1.4 2.5 2.2 1 1 2.2 1.6 H -12 +154 4028.4 + 118 +123 23 + 114 + 136 + 127 + 149 + 125 +123 22 +108 25 +105 29 +157 25 + 132 + 135 + 133 + 127 + 132 + 147 + 122 + 148 +167 13 + 112 + 118 + 121 + 158 +157 24 +129 35 + 147 +120 252.7 +139 30 +141 22 +143 22 +118 28 +134 25 +147 13 +116 15 +157 30 (km s)(cms“ 158 High (10)*+ Nil Nil Nil Nil 45 15.6 34 42 31 23 37 28 29 22 30 30 31 22 27 35 33 AV B 18 xio 13.8 Hydrogen intheGalaxyandLMC1195 9.7 4.8 4.9 4.2 4.0 3.2 3.1 1.7 2.0 3.2 5.3 3.2 3.3 1.9 2.4 2.8 2.9 2.7 1.5 1.6 2.4 2.4 7.3 3.4 2.2 1.9 3.2 8.8 1.4 1.4 1.1 3.1 2.6 1.0 +146,+252 + 170,+250 +178,+312 +160,+326 +162,+344 +172,+351 + 173,+370 + 167,+340 +182,+331 +190,+321 +176,+327 +163,+320 +152,+298 + 162,+249 + 157,+250 +160,+259 +160,+260 +162,+251 +142,+260 +202,+362 +168,+337 +178,+310 +183,+326 + 189,+328 + 150,+328 +197,+324 +160,+303 +145,+292 + 184,+289 +133,+302 +145,+298 +159,+292 +141,+300 +163,+291 + 160,+250 +160,+252 + 226,+340 +230,+359 + 205,+351+177201.1 +370 25 +203,+342 +209,+351 +209,+350 +171,+287 + 221,+358 +231,+332 + 221,+381 ■167 ,+277 + 76,- + 78,- + 87,- velocity Other range (H) + 1-2-2 + 188 +290 250.9 + 211 + 191 +181 255.0 +276 203.3 +282 181.8 +270 241.& + 211 + 209 +202 302.2 +195 301.6 + 193 (km s“)(cms" Low LMC (12)* + Nil 28 25 AV 34 35 20 13 B B B B B B B B B B B B B B B B B B B B B 18 xio 4.1 4.5 4.4 3.6 2.4 1.9 H -'H + 311 + 344 + 372 + 373 + 330 + 353 + 351 + 362 + 362 + 331 +351 25 +346 16 +360 16 + 372 + 347 + 358 + 348 +370 32 +369 22 +370 25 + 363 + 373 + 350 + 311 + 321 +359 25 +330 26 +361 20 + 360 +370 22 + 362 + 370 ■37 ■370 High LMC (13)*+ Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil AV 21 35 16 15 17 26 23 30 30 31 17 16 20 26 19 24 17 21 20 20 25 24 B 18 xio 0.9 1.9 2.6 1.8 1.1 1.2 0.9 3.8 1.6 1.5 1.4 3.6 1.8 1.7 1.0 1.8 3.8 0.9 1.2 1.1 1.5 1.2 1.8 2.4 1.9 2.3 1. 1.4 1.7 1.8 1.0 1.6 2.7 1.1 1.5 198 3MNRAS.205.1191M 1 _ Table 1-continued immediately obvious;the separationofthenegativecomponentasaresidual afterfitting profiles. The profilesFig.1(e)and (h) showthatthemuch highernoiselevelin the appearance ofthesame features innearbyprofilestowardsSk80andSkl08 (Sanduleak components at—32and+76kms~inHD5980 intheSMCwassupportedby the problemsassociatedwithidentifyingfeatures. InFig.1(a),forexample,thechoiceof local armandfromtheSMC,MagellanicStream theLMCatlinetemperaturesof0.5K or less.Thelow-intensityfeaturesthenrevealed havebeenfittedwithGaussiancurves. Gaussian curvestothestrong localprofilewasconfirmedbysimilarfeatures innearby 1196 R.X.McGee,L.M.NewtonandD.C.Morton Representative samplesfromthethreeregionsare given inFig.1,whichillustratessomeof 1970). InthecaseofHD 268605intheLMC(Fig.lb),threepositive-velocity featuresare 1'\e loeitesincolumns-!0areLSRandthose11-13heliocentric. HD 38282 HD 56402 I ID268605 HD 269357 0528-704 0528-706 0526-675 0522-679 0504-655 0 52-()7 0500-702 0459-657 0459-655 0457- 65 0456-658 0456-657 Sk -67°18 0547-695 0543-679 05 22-714 0502-658 0500-700 0459-658 0456- 64 0454-700 Source name *'Nil' indicatesthatnofeaturewasobservedintheradialvelocityrange(columns9,10,12,13). 0536-676 0532-677 0454-698 A, B,Cindicatethatlow-intensitycomponentscouldnotbedelineatedbecauseprofilesofthehigh- A dashindicatesthatnoobservationwasmadeintheradialvelocityrange(columns7,9,10,11,12,13). and 13)extendedintotheparticularradialvelocityranges. intensity* local(incolumn9),MagellanicStreamcolumns 10 and12)LMChydrogen(incolumns12 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System (D 05 2824 05 2824 05 2609 05 0200 05 0200 04 5900-6550 04 5700 04 5644 04 5600 04 5600 05 4331 05 5230 05 2601 05 2248 05 2230 05 1913 05 0400 05 0015 05 0012 04 5900 04 5900 04 5515 05 4720-692659 05 5915 05 3602 04 5410 04 5410 04 5019 R.A. Dec. Position (1950) (2) -67 3230 -67 4359 -70 3800 -70 2900 -67 3159 -67 5859 -69 1436 -65 5230 -70 1600 -70 0100 -65 5230 -65 4200 -67 5159 -69 0345 -67 3558 -71 2400 -65 3000 -65 4200 -67 1548 -70 0400 -67 4442 -69 4859 65 3000 66 2859 65 5230 65 4200 278.4 278.8 -30.9 279.4 277.9 281.4 281. 2 277.8 277.8 282.4 279.9 275 .8 276.3 276.1 281.6 281.3 -34.84.12 276.4 276.2 275.9 -36.14.12 277.2 -36.1 276.5 -36.3 278.0 277 .7 276.0 -36.3 276.3 -36.3 2 78. 281 .5 281 .2 2 78.9 coordinates £ b Galactic (3) -36.0 -35.3 -36.3 -35.4 35 .7 34.8 33.0 35.7 36.0 36.0 31.4 31 .7 32 .1 32.4 32.4 33.1 32 .7 33.3 33.4 35.6 32.4 Rdia 4 .12 4.12 4 .12 4 .12 0.82 4.12 4 .12 4 .12 4.12 0 .82 1.65 1.65 1.65 1 .-ó5 1 .'65 1.65 1.65 1.65 1.65 1.65 1.65 1.65 1.65 1.65 1.65 1.65 width velocity Band- 4í -1 (km s) -110,+270 -150,+270 (4) - 50,+450 - 20,+400 - 50,+450 - 20,+400 - 20,+400 - 20,+400 -20 ,+400 - 50,+450 - 50,+450 -80 ,+450 - 20,+450 -50,+450 - 50,+450 - 20,+400 -50,+450 - 50,+450 -20,+400 -50,+ 150 -60,+150 - 20,+400 - 20,+400 -50,+450 - 20,+400 - 20,+400 - 20,+400 120 ,+250 range 1 velocity (km s") ®->LSR -15.1 -16.0 -15.1 -15.9 -16.0 -16.0 -15.1 -15.2 -15.4 - 14.9 -15 .7 -16.0 -16.0 -15.4 -15.8 -15.5 -15.8 -15.8 -15.4 -15.8 16.0 16.0 16.0 15.6 15 .1 15.5 15.9 15.1 (5) -2 18 (cm) noi se ao 0.5 0.5 0.5 0 .1 0.5 0.6 0.5 0.6 0.6 0.6 0.6 0.5 0.6 0.6 0.2 0.6 0.6 0.5 0.7 0.6 0.2 0.6 0.6 0.1 0.6 0.6 0.4 0 .2 AN RMS (6) h <-50,+32 -1 -55,+35 -50,+40 -42,+34 -54,+36 -50,+57 -48,+37 -53,+42 -90,+40 - 50,+67 -90,+45 -35,+40 -30,+40 -37,+35 -78,+55 -46,+42 -54,+40 velocity (km s) - ,+67 - ,+34 - ,+50 - ,+35 - ,+34 - ,+29 - ,+34 - ,+35 - ,+34 - ,+35 - ,+34 range Local (7)t 198 3MNRAS.205.1191M -1 of thelow-intensityfeatures. tively thenameofstar orradiosourceinthedirectionofobservation, celestial width halfmaximum,FWHM),AV,andcolumn densities, N^,forindividuallinecompo- total rangeofradialvelocity ofeachobservation(bothinkms)andconversion ofhelio- level (ATVh)inthevalues of7V.Thislevelwasderivedbytakinganimaginary instrumental centric toLSRradialvelocities ateachposition.Column6givesanestimate ofthenoise coordinates fortheepoch 1950,galacticcoordinates,bandwidthofeach channel andthe nents isgiveninTable1.Thetablearrangedas follows:Columns1to5containrespec- Magellanic StreamandsomeLMCobservationsdoes notpreventrecognitionandanalysis H 1¿z- + 1.3 + 4.1 + 1.2 + 1.0 + 1.1 -0.2 183.1 -0.5 202.9 -0.6 142.7 -0.3 165.7 +0.5 162.5 + 8.8 + 7.5 -1.6 -1.3 + 0.1175.0 + 1.1 + 1.0 +1.5 192.8 +0.5 202.7 -4.9 154.3 -0.7 157.5 -0.4 -2.5 -2.9 -2.3 -1.6 (km s")(cm“sd(cm" 4.4 206.1 0.0 The reductionofthe21-cmprofilesintoradial velocities, V,linehalfwidths(i.e.full- © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Local (8) t AV N, 16 18 15 18 17 15 15 20 20 13 14 13 14 20 18 20 15 x20 10 6.3 4.3 6.2 4.9 5.5 2.5 2.8 4.8 5 .1 2.6 2.7 3.6 5.3 3.5 5 .5 3.2 5.0 +52 457.4 +84 130.9 + 71 +50 252.7 +83 181.6 +45 274.9 +57 216.1 + 61 +59 232.1 +65 274.9 +96 142.6 +50 224.4 +54 286.1 +70 3021.9 + 7530 + 65 + 81 -32 127.7 -31 129.4 -32 - 34 -32 116.4 -31 137.8 +44 304.9 +62 374.7 -37 187.9 +93 254.1 +37 182.6 V AVN,, Intermediate Nil Nil Nil Nil (9)* + 23 2.1 2 1.2 11 5.0 25 1.4 21 1.9 11 5.2 A A A A A A 1 xjQ 8 1.1 +124 453.3 +146 2414.9 +133 402.2 +114 200.7 +135 2511.4 +139 25 +144 28 +117 4018.2 +138 232.9 +143 253.6 +125 262.4 +144 272.5 +144 2513.7 +133 201.1 +111 171.5 +142 201.8 +118 304.9 +139 382.1 +144 2824.5 +107 221.6 +118 266.2 +117 304.4 +156 404.4 +118 235.0 High dort Nil Nil Nil Nil Nil Nil AV N, 1 xlQ 8 Hydrogen intheGalaxyandLMC1197 2 .3 5 .1 + 210,+340 +210, - + 205,338 + 228,+350 + 190,+320 +201, - +210,+344 + 190,+390 + 210,355 +210,+340 + 210,+370 +165,+350 + 190,340 +215,+350 + 210,+372 + 190,+360 + 190,+340 + 200,390 +175, - + 212,+367 + 210,395 + 200,+590 + 210,395 + 200,+390 + 205,+390 + 190,385 velocity (km s-d Other range ddt -2_ +196 19 +204 30 +223 25 +194 18 +183 45 +216 21 +195 14 +188 355.7 + 177 (km s-d(cm)sd V AVN 210 36 190 18 82 h 190 27 Low IMG (12)*t C C C C 18 <10 12.5 4.9 4 .1 3.8 2.3 1.0 1 .0 4 .9 5 .9 5 .7 3.8 1.5 +4251 + 589 + 350 + 348 + 357 + 346 + 420 + 547 + 360 + 372 + 338 + 375 ■359 363 360 392 High LMC (13)*t 2 3 19 4 5 20 3 5 18 15 5 10 C 2 1 8 14.8 11.5 10.2 15.5 (cm") x 10 0.5 0.5 1.4 4.0 2.9 0 .7 3 .2 7.0 7.4 H 198 3MNRAS.205.1191M 1 1 1 1h 1 182 velocity Hiwhichwepresumeisextragalactic.Column11liststhefullrangeofvelocitiesat depth, usingtheformula all thevaluesofinTable1havebeencalculatedonassumptionverylowoptical profile withamaximumtemperatureequaltothe1onoiselevelandtypical FWHM of25kms"andcalculatingacolumndensity,whichistabulatedasA7V.Notethat kms") respectively.Alltheradialvelocitiesinthispartoftablearereferredtolocal of thestrong(linetemperatures5to20K)localHilinereachzero,whilecolumns8,9and (between radialvelocities~+30and+100kms'),high+100+170 meters areincludedincolumn9.Thelastthreecolumnscontaininformationonhigher- standard ofrest(assumedtoberecedingfromtheSunat20kms”towardsRA18,Dec. the totalrangeofradialvelocitiesinlocalgas,i.e.atwhichintensities The nextfourcolumnscontaininformationaboutHiassumedtobegalactic.Column7is + 30°,epoch1900).Insomecasesnegativevelocitycomponentsweredetected;theirpara- the linecomponentsis±3kms”andinhalfwidths4s". and thelast28directionsinLMC.Finally,columns1213giveF,AFA^ zero intensityofthestronglineoriginatingfrommainobjectinobserveddirection, recording nolow-intensitydetection.AsummaryisgiveninTable2showingaveragevalues e.g. thefirstthreesourcedirectionswereinSMC,next47MagellanicStream Ar= 1.823xlOjjWHatomcm“. components ofHiarepresentthroughoutthewholeregion,withonly8percentcases fore notuniformorevenrandom.However,thedataindicatethatlow-intensity degrees inthesky.Thesamplingwasfixedbyotherobservationalrequirementsandisthere- sources, theseradialvelocitiesareheliocentric.Theestimatederrorintheof for gasdesignatedlowandhighLMC.Followingtheusualconventionextragalactic H 10 containtheF,AFandNforHilinecomponentsdesignatedstronglocal,intermediate H H n 1198 R.X.McGee,L.M.NewtonandD.C.Morton velocity, F;FWHM,AV\columndensity,A^h- Table 2.Summaryofthemeansparametersvarious21cmH-linecomponents:radial * RadialvelocityrelativetoLSR. High LMC,all Negative, all HI component t Radialvelocity relativetotheSun. Low LMC,all Intermediate, all High (galaxy)all Local mainbody © Royal Astronomical Society • Provided by theNASA Astrophysics Data System The datainTable1coveracomparativelysmallregionofapproximately730square Magellanic Streamonly Magellanic Streamonly LMC only LMC only LMC only LMC only SMC only 78* No. 40* 65* 62* 51t 21* 24* 38* 17* 13t 16t 241 4* -1 (kms) V + 196.9 + 131.7 + 130.7 + 367.3 + 360.3 + 195.8 + 133.1 -39.6 + 59.4 + 65.5 + 73.0 +56.2 -1.8 : ± 16.8 ± 10.0 ± 2.8 ± 15.7 ± 21.5 ± 16.1 ± 16.1 ± 3.6 ± 12.4 ± 13.9 ± 26.0 ± 21.2 ± 13.7 1 27.3 ±7.1 24.5 ±6.7 24.5 ±6.9 AF 25.3 ±9.1 25.8 ±7.8 27.0 ±6.9 24.9 ±7.4 18.8 ±5.8 (km s") 27.3 ±12.1 27.3 ±7.1 20.3 ±4.7 17.8 ±3.8 23.3 ±8.2 2 -218 (3.2 ±1.3)X10 7V 4.2 ±4.6 6.8 ±3.6 4.3 ±3.1 4.6 ±6.2 4.9 ±5.4 cm X10) 6.0 ±6.2 5.3 ±5.2 3.8 ±2.5 (H atoms 5.8 ±5.0 3.0 ±1.3 3.6 ±3.0 H 3.0 ±3.3 198 3MNRAS.205.1191M -1 -11 _1 -1 -1 1 _1 = ±1 When ahistogramoftheradialvelocitiesisplotted(Fig.2)reasonsfordesignations few innumber;theyarediscussedSection6.Thestronglocalgasisnotunderconsidera- of thevariouscomponentsbecameapparent.Thenegativearecomparatively intensity Hicomponents-negative,intermediate,high,lowLMC,highLMCandforthe histogram at~±20kmsarenotnecessarilyreal. tion herebutthehistogramillustratesitsnarrowrangeofvelocities—allcontainedwithin 4 Distributionofradialvelocities strong localcomponent. for thethreeparameters—radialvelocities,lineFWHMsandcolumndensitiesoffivelow- values). Inthecaseofhigh-velocitycomponent,averagesstayclosetooverall one. components (seeFig.2).TheHiinthemainbodyofLMCiscontainedthreelarge the high-velocitycomponentextendsto+170kmswithameanof130.7s“. associated withourGalaxyintointermediate-andhigh-velocitycomponentsatF= — 65and+45kms.Thewidewingscouldhideweakcomponents,sothedipsin especially inviewofthehighvalue+73kmstowardSMC(representingonlyfour Magellanic StreamandLMCdodifferby~lOkms(seeTable2),butnotrendisclear, The averagevaluesoftheintermediatecomponentstakeningeneraldirections frame is-16kms~L mately ll.Skms"(McGee&Milton1966)andwithcolumndensities~3ordersof (heliocentric) approximately,andmayblanketsomeoftheweakhighgalacticlowLMC + 100kms.Thentheintermediate-componenthasameanvelocityof+59.4kmsand for theMagellaniccomponents. InthedirectionofLMCcorrectionfromheliocentric toLSR sheets ofgascentredonradialvelocities+243,+273and+300withdispersionapproxi- convention, thevelocityscale isrelativetotheLSRforgalacticcomponentsand relative totheSun Figure 2.Histogramofradial velocitiesoflow-intensityHifeatures.Notethat,following theusual Flsr 10kms"—comparedwiththelargespreadofzero-intensitycut-offvelocities LSR _1 The histogramshowsthatitisreasonabletoseparatetherestofgasapparently The strongcomponentsoftheMagellanicStreamextendfrom+130to+230kms © Royal Astronomical Society • Provided by theNASA Astrophysics Data System There appearstobenocorrelationbetweentheradialvelocitiesandgalacticlongitudes. Hydrogen intheGalaxyandLMC 1199 198 3MNRAS.205.1191M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 the ratioofcolumndensities shouldgivetheoxygenabundance(exceptwhere oxygenmay are fromRoss&Aller(1976). SinceOiandHihavenearlythesameionization potential, curve ofgrowth,arecompared withourtotalHidensityinTable4.Thesolar abundances enough toestimatesome columndensitiesorlowerlimits.Theirresults,assuming asingle these cloudsmustbeatconsiderabledistancesbelow thedisc. that thevelocityranges(definedatzero-intensitycut-off)incolumn11ofTable1do close tothisrangehavebeencalledlowLMC(F©=+196.9kms')andhigh(F between +230and+310kms”inthehistogram.Thecomponentslyingoneitherside magnitude abovethoseofthelow-intensitygas.Thusweomitconsiderationvelocities several elementsat+70 and +120kms'fromthestrongabsorptionnear 0kms"well and UVwavelengths. indicate adependenceongalacticlongitude.Onthelowsidevalueschangefrom: the averageandintermediatecomponentsgreaterby~10kms'inLMCdirections (1981) withourclosestHivelocities.TheUVhighvelocitiesaregreaterby~Skms"on 4.1 NOTEONMAGELLANICSTREAMREGION grouped withinafewkilometrespersecondoftheoverallmean25.1kms'.Thevalue the planeandperpendiculartoit.Neverthelessat suchradialvelocitiesitisbelievedthat distances thatcorrespondtothesevelocitiesdepend ontheadoptedvariationofvelocitiesin lines. Thusitisreasonabletoassumethatweare observing thesamecomponentsatradio 25-kms" velocityresolutionoftheIUE,inaccuracies ofitswavelengthscaleandthe Table 3comparestheUVvelocitiesofweakerlow-ionizationlinesSavage&deBoer & Murray1974)andweseefromTable2thatF(lowLMC)=+195.8kms',itwould Magellanic StreamliesinfrontoftheLMC—SMCbridgeregion(see,e.g.Mathewson,Cleary The HiinthemainbodyofMagellanicStreamwillnotbediscussedhereexcepttonote contrasts withthemeanwidthof78examplesstronglocalgasIT.Skms". 5.1 COMPARISONOF21-CMANDULTRAVIOLETLINES therefore seemthatthe10casesmayrepresentgasinvicinityofLMCenvelope. on thelow-velocitysidetowardsMagellanicStreamwherelow-intensitylineshavebeen lie onthehigh-velocitysideofMagellanicStreamprofiles.Thereareonly10othercases + 360.3kms')respectively. — perhapsbymorefortheSMC.Thesedifferencescanbeexpected,considering 5 Intermediate-andhigh-velocitygas:evidenceforHigalactichalo delineated, theiraveragevelocitybeing+197.4±11.7kms".Inthesedirectionsthe decreasing /),onthehighsidevalueschangefrom:~+250kms'at1=295°to blending ofsomelines,aswellourownlowS/N ratioandpossibleblendingoftheHi of +355.8±17.5kms",suggestingthatthisgasispartthehighLMC(mean + 367.3±26.0kms",seeTable2). ~+375 kms'at/=280°(+7s"deg"withdecreasing/). 16.1 kms",andthemeanofall24high-velocitycomponents is+131.7±13.9kms'.The @ Flsr ~+145kms"at1=295°to230/=280°(+5s'deg"with 1200 R.X.McGee,L.M.NewtonandD.C.Morton 1 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Towards HD36402,Savage&deBoer(1981)were abletoseparatethelineblendsof Towards theLMCmeanvalueofall21intermediate 21-cmcomponentsis+65.5± The meanvaluesoftheFWHM(AF)alllow-intensitycomponentsaresimilar— The fewlow-intensitylinesat+270to+190kms"near1=285°(column12,Table1) The 35examplesonthehighsideofMagellanicStreamprofileshaveameanvelocity 198 3MNRAS.205.1191M become associatedwithgrainsormolecules).Weseethatoxygenisdepletedbyafactor somewhere between2and10comparedwiththesolarabundance.Theionizationpotentials of Mgil,AlSiiiandFenimplythattheyshouldbethedominantspeciesinHiregions. lie manykiloparsecsbelowthegalacticplane. including HD36402(Savage&deBoer1981). Theindividualcolumndensitiesand whereas, accordingtoSavage&deBoer,thelinestrengthsaremoreconsistentwithsimilar also possible.Inthiscase,however,theeffectshouldbegreatestforMgnandleastSin, abundances. Aluminiumandsiliconappeartobedepeletedbynomorethanafactorof2 Absorption byMgn,SinandFenformeddielectronicrecombinationinHuregionsis abundances arequotedinTable5.Againweseethat thedepletionsaresmallorzero.Thus compared withsolarabundances. (HD38268), R139and R145, whichareclosetothe30Doradusnebula. Theyarealso iron isnearthesolarabundanceinbothintermediate- andhigh-velocityclouds,which The positionsoftheseobjects aregivenatthefootofTable6. HD38282 at21cm.Thus comparisonsoftheopticalandradiolineprofiles maybemade. sufficiently wellcovered by the14.9arcminbeamwithwhichweobserved thenearbystar Blades (1980)hasobserved interstellarCan(andNai)inthedirection ofstarsR136 5.2 COMPARISONOF21-CMANDVISIBLELINES 1 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Fen componentsnear+60and+130kms”were resolvedforthreeoftheLMCstars, 1 Table 4.Combinedabundancesincloudsat+70and+120kmstowardsHD36402. Mg II Fell Alii Ol HI Ion Si II Table 3.ComparisonofUVand21cmradialvelocities(LSR). Star In theLMC In theSMC LMC mean HD 5980 Sk 108 HD 268605 Sk 80 HD 36402 Sk -67°18 HD 38268 HD 269357 HD38282 >13.1 >14.2 >13.8 2 14.7 to15.5 14.4 ±0.1 18.94 Log [V(cnr)]V/V(HI)] 1 (+85) (± 4.7) UV Intermediate + 60 (km s") + 65 + 70 + 60 + 60 + 60 + 62.5 >-4.7 >-5.8 >-5.1 -4.2 to-3.4 -4.5 Hydrogen intheGalaxyandLMC (±13.7) + 74 HI + 69,+80 + 76 + 52 + 45 + 52 + 75 + 53.2 + 37 + 58 Log -5.60 -3.17 -4.60 -4.45 [N/N (H)] -4.46 @ 1 (±8.5) High UV (km s") + 130 + 120 + 140 + 130 + 129 + 125 >-0.24 >-0.30 >-0.68 Log depletion -1.07 to + 0.06 (±13.0) HI + 133 + 117 + 138 + 124 + 107 + 123.8 0.27 1201 198 3MNRAS.205.1191M _1 -1 1 1202 clouds inourGalaxyand the LMC,andthreeweakfeaturesatV(LSR)=+54.5, +107.5and + 133.5kms.Songaila(1981) observedtheCanKlineinHD38282with acomponentat + 62kmsbutnoneat 130km s'. hms hms hm hms Table 6.ComparisonofCaIIandHI(21cm)towards30Doradus.* Weak features(LSR) Strong features(heliocentric) Star References a, Blades(1980);b,presentwork;c,radialvelocityandcomponent sizesbyRadhakrishnanetal maximum). 05 3913,-69°03'43";R1393902s,06'33"; R145(HD269928)053916, * Thepositions(1950.0)are:HD38268(R136)0539 03s, -69°07'40";HD38282(R144) (1981). (1972); columndensitiescalculatedbyusfromtheirfig. 4assumingaTof80K;d,Songaila -69° 07'40";30Doradus05390,07'00" (the positionofthe21cmcontinuum © Royal Astronomical Society • Provided by theNASA Astrophysics Data System s For HD38268,Blades(1980) foundfourstronglines,whichheattributed tomaingas HD 38268 HD 38268 R145 HD 38268 HD 38268 R145 R139 R145 R145 HD 38268+54.5 HD 38282 HD 38282+62 HD 38268+107.5 HD 38282 HD 38268+133.5 Table 5.Separateironabundancesinintermediateandhigh-velocityclouds. Star Intermediate-velocity gas High-velocity gas HD 3640214.0 HD 268605 HD 3828213.6 HD 26860513.7 HD 36402 HD 38282 R. X.McGee,L.M.NewtonandD.C.Morton 1 + 2841 + 277) + 261 + 250 + 3011 + 300) Call HI (km s") Radial velocity + 18 + 17 + 18 -2 TV (Fell) (cm) Log 13.5 14.1 13.8 + 247 + 282 + 268 + 296 + 107 + 138 + 15.5 + 37 + 87 + 58 -2 7V(HI) (cm) Log 18.64 18.34 18.41 18.20 18.64 18.69 2 12.08 12.08 12.46 12.15 Ca IIHI Column density 12.53 11.90 12.46 12.38 12.53 Log [N(cm")] 11.41 11.63 11.04 1 + 117 + 133 (km s") + 107 V (HI) + 50 + 45 + 37 20.51 20.84 20.97 20.90 20.42 17.85 18.42 17.60 18.20 17.79 TV(HI)] Log -4.99 -4.64 [TV (Fell)/ -4.81 -4.54 -4.54 -4.70 ratio Abundance References Log ^(CalD 9.00 6.44 8.05 8.36 7.96 7.89 8.31 8.89 8.43 8.46 6.22 6.34 7.16 TV(HI) depletion Log -0.39 -0.21 -0.04 + 0.06 + 0.06 -0.10 a, b a, c a, c a,c a,c a, b a, b a, c a, c b b, d b a, b a, b a,b 198 3MNRAS.205.1191M 1 1 1 1 1 1 1 prominently enoughfromthenoise.Radialvelocitiesandcolumndensitiesforthesefive components areincludedinTable6.ThreeoftheweakHifeatures(at+58,+107and additional componentsarenotreportedinTable1becausetheydostandout but anextremelywidezero-intensityvelocityrange,onaveragefrom—67.5±13.2kms' has amoderatehalfwidth-onaveragethe78sampleshaveFWHM=17.8±3.8kms"— of HD38268and38282inthe30Doradusnebula of theLMCinvelocityrange+170to near thelocalgas.Itcanbeseenfromcolumns8and7ofTable1thatstronggas De Boer,Koornneef&Savage(1980)detectedultraviolet absorptionlinesinthedirections low-intensity levels(<0.4K),especiallyatl^300°andlessso/276°. to +44.6±12.1kms'.Theprofilesaremarkedlyskewedtowardsnegativevaluesatthe 6 Low-intensitygasatnegativevelocities large absorptionfeaturesintheHi21-cmprofileof30DoradusdetectedbyRadhakrishnan regions ofhothalogasin front oftheLMC. many otherprofiles,smoothextendedwingsprobablyconcealthepresenceofindividual assumed Tg=80K. et al.(1972).Opticaldepthsandhalfwidthswereavailablefromtheirfig.4wehave + 87kms')havepossibleCanorHcounterpartfeatures,whichcanalsobeseenin It ispossiblethatathirdlow-intensitycomponentdisplayingnegativevelocitiespresent wavelengths. the calciuminHicloudsweremainlyCanandnotattachedtograins,logratio features listedwehavemadeestimatesofthecolumndensitiesatfourradialvelocities + 138kms')haveCancounterparts(discussedbyBlades1980);theothertwo(at+37and ionization-stage ions,de Boer &Savage(1980)concludedthattheyhadprobably detected Aim, SiivandCiv.After obtainingfurtherinformationonthestarsSk 108, HD36402, Sk —67°18andHD269357, andconsideringthestrength,widthradial velocity ofhigh- 7 LMChalogas somewhat higherthanthatfortheintermediateand highgalacticcomponents(seeTable2). features lie~2kpcbelowthegalacticplane. components. ThehistograminFig.2showsthatthesecomponentsofaveragevelocity than inthestrongfeatureswhichrepresentourownspiralarmandarmsorlargesheets Blades’fig. 3. + 220kms'(heliocentric). TheionsconcernedwereFen,Alii,Oi,Sin, Cn,Cn*, calcium, whichseemstobelessattachedgrainsincloudsdistantfromthegalacticplane. of hydrogenintheLMC.Thisisusualpatternforahighlyrefractoryelementlike depletion appearstobepresentinalltheclouds;however,thisislesssoweakfeatures column densitiescouldbeunderestimatedinsomecasesowingtosaturationofthelines, — 39.6±10.0kms'lieinsidetherangeofzero-intensity widths.Weestimatethatthese should bethesameassolarvalueof—5.65(Ross&Aller1976).AlthoughCan Full verificationoftheweaklinesrequiresadditionalobservationsatbothradioandvisible 182 We considerthatfiveweakcomponentsarepresentat21cm(Fig.Id).Thethree The abundancecolumninTable6comparesthedensitiesofCanandHi.If © Royal Astronomical Society • Provided by theNASA Astrophysics Data System The propertiesofthelinesaregiveninTable6.InordertomatchstrongLMC The averagecolumndensityofthenegativevelocity clouds,6.8x10atomcm',is Only 17low-intensitycomponentshavebeendelineatedatnegativevelocitiesand,on Hydrogen intheGalaxyandLMC 1203 198 3MNRAS.205.1191M 1 18-2 1 _1182 -1182 1 182 _1 18 1 and mustbeinthesamegasclouds.Thereare24HilinecomponentsofP=+196.9kms“. velocities todateintheLMC,butdeBoer&Savage(1980)detectedaweakcomponentat rotation curveoftheLMC. probably representgasintheLMC-SMCbridgeregion.Themeanvelocityforthese35was conditions asthegalactichalogas(comparevaluesinTable2).Thusourobservationswould The AF=25.8kms"andjV=3.8x10cmindicatethattheHiexistsinsame overall meanasgiveninTable2was+360.3kms".WebelievethatthisHicomponentwith body oftheLMChaveahigherVof+367.3kmsand7V5.8x10cm".The Magellanic Streamobservations.Nevertheless,aswehavepointedoutinSection4,they support thespeculationofhalogasinfrontLMC.Onotherhand,Feitzinger& intend toundertakeanextensivesurveyoflow-levelHioverthewholeLMC(andSMC)area + 356kms,whilst7Vwas1.7x10cm".The16sourcesfromdirectionsinthemain Schmidt-Kaler (1982)arguethattheopticalandUVabsorptionlinesfitwellintoabranched HD5980. OurHiobservationsinthisdirectiondidnotextendtovelocity. + 300kms"intheSMCforCn*,Sin,Sim,SiivandCivfar-UVspectraof AF= 23.3kms”and7V=3.0x10cm“couldrepresenthalogasonthefarsideof 1204 R.X.McGee,L.M.NewtonandD.C.Morton LMC. h H We havedetectedfiveindividuallow-intensitycomponentsofneutralhydrogeninthe H We thankK.J.Wellington fortheopportunitytousehisprototypeof cooled21-cm galactic longituderange276°to302°towardstheSmallandLargeMagellanicClouds.The H components atmeanLSRradialvelocities—40,+59and+131kmsarethoughtto stars providessomeabundanceestimates.Theyare~0.1to0.5solarforoxygen,^0.2 consistent withobservationsofultravioletandvisibleabsorptionlinesinthesamedirections. represent threelevelsofgascloudsinthegalactichalo.Thelattertwovelocitiesare who producedtheextremely reliable21-cmreceiverusedintheother sessions, andto front endinthefirstsession. WearealsoverygratefultoM.W.Sinclairand J.D.Murray, Acknowledgments contain muchlessmetallicmaterialwithhighcondensation temperatures. results fromtheultravioletandvisibleinterstellarabsorptionlinesinfrontofcertainLMC 8 Conclusions the galacticdiscandmoresimilartointercloudor high-latitudematerialwherethegrains in someofthemetals,depletionsaregenerally lessthanthosewhichoccurinclouds for magnesium,>0.5solaraluminiumandsilicon,~0.4to1timesiron, is foundonlyat21cm,indicatesthepresenceofahalo aroundtheLMC. + 59kms”and5x10at131km.Atthetwopositivevelocities,comparisonwith in anattempttoverifythepresenceofsuchahalo. (1980). Thisfourthcomponent,consideredwiththe fifth(at+310to+430kms"),which part oftheultravioletabsorptionlinesatsimilar velocities reportedbydeBoer&Savage B.MacA. Thomas andG.L.Jamesfordiscussion andadviceonthe strayradiationproblem. ~ 0.03to0.25forcalcium.Althoughcorrections may beneededforunobservedionstages 1 182 1 We regardtheresultsmerelyasanindicationofagaseoushalosurroundingLMCand © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Our ‘lowLMC’Hi(seeFig.2)occupiesthesamevelocityrange,+170to+220kms", No ultravioletorvisibleabsorptionlinesseemtohavebeenreportedatthesehigher In thecaseofour‘highLMC’components,thereare51samples,35whichcomefrom The Hicolumndensitiesaveragearound7xl0cm'at—40kms”,4x10 The fourthHicomponentbetween+170and+220kms” (heliocentric)isthecounter- 198 3MNRAS.205.1191M de Boer,K.S.,Koornneef,J.&Savage,B.D.,1980.Astrophys.J.,236,769. de Boer,K.S.&Savage,B.D.,19%0.Astrophys.J.,238,86. Blades, J.C.,1980.Mon.Not.R.astr.Soc.,190,33. Mathewson, D.S.,Cleary,M.N.&Murray,J.D.,191A.Astrophys.J.,190,291. Gondhalekar, P.M.,Willis,A.J.,Morgan,D.H.&Nandy,K.,1980.Mo«.Not.R.astr.Soc.,193,875. Feitzinger, J.V.&Schmidt-Kaler,Th.,\9%2.Astrophys.J.,257,587. McGee, R.X.&Milton,JaniceA.,1966.Aust.J.Phys.,19,343. References Radhakrishnan, V.,Brooks,J.W.,Goss,W.M.,Murray,D.&Schwarz,U.J.,1972.Astrophys.Suppl. Sanduleak, N.,1970.CerroTololoInter-AmericanObservatoryContributionNo.89. Ross, J.E.&Aller,L.H.,1916.Science,191,1223. Songaila, Antoinette,\9%l.Astrophys.J.,248,945. Savage, B.D.&deBoer,K.S.,19%l.Astrophys.J.,243,460. © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Ser., 24,1. Hydrogen intheGalaxyandLMC1205