19 91MNRAS.24 9. .145B A 2 2 1234 1 A surveyofinterstellarCaiiabsorptioninthehaloeslow-redshift Space TelescopeScienceInstitute,3700SanMartinDrive,Baltimore,Md.21218,USA Accepted 1990October14.Received10;inoriginalformAugust Anglo-Australian Observatory,POBox296,Epping,NSW2121,Australia AstronomyCentre,UniversityofSussex,Palmer,BrightonBN19QH David V.Bowen,MaxPettini,MichaelPensionandChrisBlades galaxies Mon. Not.R.astr.Soc.(1991)249,145-158 RoyalGreenwichObservatory,MadingleyRoad,CambridgeCB3OEZ The ideathatthenarrowmetalabsorptionlinesseenin hypothesis amongmostobservers. Thesizeofgalaxyhaloes spectra ofsomeQSOsarecausedbygalaxiesintervening Steidel &Boksenberg (1988).Tytleretal. found thatthe along theQSO’sline-of-sight nowseemstobeaworking (0.1galaxy ofluminosity L*(the‘fiducialluminosity’ discussedby Lapparent, Geller&Huchra (1989), andassumingthatthe Zabs 0.51is0.27forequivalentwidthsW(A2796)>0.6Ä haloes aresphericalandthatthere isnoredshiftevolutionin A A 3- = 0.020±0.005hMpc(h=H/10,whereHisthe 0 19 91MNRAS.249. .145B l= -1 146 D.V.Bowenetal. 1 (e.g. Sargente/ß/.1979). Schechter 1976)mustbe25and40h~kpc(go0)to tion occurswithinextendedgalaxyhaloesisprovidedby account fortheaboveincidenceofMgnabsorptionatz-0.5 imaging studiesofQSOsalreadyknowntoexhibitinter- mediate-redshift Mgnlines.Galaxiesatthesameredshiftas the absorptionsystemsarealmostalwaysfoundcloseto predicted fromthestatisticsofabsorption-linesurveys quasar line-of-sight,atseparationscomparabletothose less, itisstillunclearwhetherthetrueabsorberliescloserto the QSOsight-linethanidentifiedone(despitethis (Bergeron &Boissé1991,andreferencestherein).Neverthe- coincidence), whetherthesegalaxiesareunusualinposses- of sometheabsorptionUnes,sometimesexceeding sing similar,L*,luminosities,andwhetherthevelocitywidths clouds distributedinagalactichalo. investigation tothepresentepoch,andexaminesight- mediate-redshift studies-istoextendtheabsorption-line one whichwouldcomplementtheanalysisofinter- 200-300 kms,canbeunderstoodintermsofdiscrete lines ofQSOswhichliefortuitouslybehindgalaxieswhose lines haveonlybeenaccessiblewiththeInternationalUltra- discerned. Unfortunately,untilrecently,low-redshiftMgn existence isalreadyknown,andwhosepropertiesareeasily required toachieveanequivalentwidthlimitlowenough this typeofwork.TypicallywithIUE,theexposuretimes long. Instead,observershaveelectedtosearchforoptical detect MgnatGalacticstrengths(^1-2Á)areunacceptably lines ofCaiiand,morerecently,Naiatthegalaxy’sredshift. in theouterregionsofgalaxiescanabsorptionbe was foundbyBoksenberg&Sargent(1978)tocauseCan maps thattheabsorbingmediumaroundNGC3067,which confidently attributedtoasphericalhalo.Carilli,van Gorkom &Stocke(1989)haveshownfrom21-cmemission This, theysuggest,istheremainingevidenceofgalactic the galaxytowardspositionofquasarandbeyond. halo noranextendeddisc,butinatailwhichextendsfrom absorption inthespectrumof3C232,liesneitherwithina violet Explorer(IUE),whichhastoosmallanaperturefor cannibalism. Bergeron,D’Odorico&Kunth(1987)have is duetodisrupteddiscgasintheESOgalaxy1327—2041, suggested thatCanandNaiabsorptioninPKS1327-206 and asimilarscenariohasbeenproposedbyCarilli&van Hunstead &Murdoch1981),isthatitoccurswithinthe Klemola cluster.Anotherplausibleexplanationforthis Gorkom (1987)toaccountfortheabsorptionseenin edge-on discoftheforegroundgalaxy,wherecolumn absorption aswellthatseentowards0446-208(Blades, density ishigherthanthatwhichwouldresultifagalactic 2020-370 (Boksenbergetal1980)bygalaxieswithinthe disc isinterceptedface-on(Bowen&Pettini1991).More this lastcasethemorphology oftheinteveninggalaxy Nai componentswithparticularly strongequivalentwidths, recently. Wombleetal(1990)havereportedtwoCanand separated by200kms~inthe spectrumof0248+430;in appears irregular. pairs arethat(i)italwaysappears tobemuchstrongerthan that observed in ourownGalaxy(aswellas mostcasesof Compelling evidenceinsupportoftheviewthatabsorp- One obviousapproachtoresolvetheseproblems-and However, innoneofthecaseswhereCanhasbeenfound Two conspicuousfactsabout theabsorptioninallthese © Royal Astronomical Society • Provided by the NASA Astrophysics Data System l l l 2 within about11h~kpcofthegalaxycentre. galaxies -seeBowenetal,inpreparation),and(ii)itoccurs absorption seeninsight-linestowardssupernovaeexternal have alwaysbeenreportedintheliterature.Ifgalaxies described aboveareunusualinsomeway,whatthenisthe QSO-galaxy pairsinwhichabsorptionhasnotbeenfound galaxies? Withoutpublishingthenon-detectionsaswell, impossible toestablishifthereisanydifferencebetweenlow- total extentanddistributionofCaninpresent-dayhaloes cross-section forabsorptionofmoretypical,quiescent and discsremainsunknown,withoutthisknowledgeitis and intermediate-redshiftgalaxies.Thenon-detectionof Jenkins (1986,hereafterMYJ),whoobservednineQSO distribution ofneutralgascanbewithingalacticdiscs. Can intheMrk205-NGC4319QSO-galaxypair(Bowen galaxies. Noabsorptionwasfound,thoughthesetofequiva- section ofpresent-daygalaxieswasbyMorton,York& et al1991)hasalreadyshownhowinhomogeneousthe from <240mÀto<57(2a).MYJconcludedthatCan lent-width upperlimitswasfairlyinhomogeneous,ranging was detectableouttoradiiofbetween8andISh~kpc,or sight-lines passingwithin40and195h~kpcofforeground of thegalaxyatasurfacebrightness/¿b=25magarcsec". 0.6 to1.4timesD(0),whereistheopticaldiameter we formanunbiasedsampleofQSO-galaxypairs,andin lower andmoreuniformequivalent-widthlimits.InSection2 pairs withseparationslessthanthoseobservedbyMYJto discs andhaloesbyreportingobservationsofQSO-galaxy construct alargeunbiasedsampleofQSO-galaxypairs, of theequivalentwidthslines-wherefoundplus Section 3wepresenttheQSOspectraandmeasurements of ourresultswiththosefortheintermediate-redshiftMgn epoch. Wealsoincludeabriefdiscussiononthecomparison quantify theCancross-sectionofgalaxiesatpresent combining ourdatawithotherspublishedpreviously,and some estimateoftheircolumndensity.InSection4we be highcomparedtotheoveralldistributionwithinagalaxy. position withinahostgalaxyis,insomesense,privileged. external galaxiesseeninthespectraofsupernovae,astheir absorbing galaxies. Accordingly, theresultsfromsupernovaesight-linesarecon- Often theyoccurwherethedensityofinterstellarmetalsmay preparation). sidered togetherinaseparatepaper(Bowenetal, The primarysourceofQSO-galaxy pairsusedforthiswork 25 2 OBSERVATIONSANDDATAREDUCTION £(QSO)<16.9 list ofobjectswascollatedwith is thecompilationbyMonket al(1986)fromwhichaninitial 2.7.7 Initialselection 2.1 ObservedQSO-galaxypairs (1) Furthermore, itisnotcleariftheobservationsof The firstsystematicattempttoestabhshtheCancross- In thispaper,wecontinuethesearchforCaningalactic The presentanalysisdoesnotincludetheabsorptionby 1 ¿><50/T kpc, 19 91MNRAS.249. .145B -2 where pistheseparationbetweenQSOline-of-sightand were observedinthissurvey.Thez(column2)andQSO the galaxynucleusonplaneofsky.Thefirstthese were selectedpreferentially.Noselectionwasmadeonthe Pairs weredrawnfromthisinitialsetbasedfirstontheir width limitswithreasonableexposuretimesatthetelescope. criteria wasbasedontheneedtoachievelow-equivalent- basis ofthemorphologyinterveninggalaxy. accessibility intheskyduringobservingruns,and magnitude (column3)aretakenfromHewitt&Burbidge secondly ontheirseparations:thosewithsmallseparations minor diametersoftheinterveninggalaxy(=seci,whereiis (1987) ifthequasarislistedtherein,orelsefromSchmidt& mag arcsec.£>(0)25(column7)istheisophotalmajor the galaxyinclination;/=0isface-on),reducedtoju25 Green (1983).R(column6)istheratioofmajorto Where thesevaluesarenotavailable incatalogues,theyhave diameter inarcmin,statistically correctedtoappearface-on. been estimatedbymeasuring RandD(takentobethe maximum diametermeasurable) onthePalomarSkySurvey (PSS) Oplates,andcorrecting forinclinationusingthe em methods outlinedbydeVaucouleurs, deVaucouleurs& Corwin (1976). Inthecaseofanonymous galaxyinthe B 25 25 In Table1,welistthe12QSO-galaxygroupingswhich Table 1.ObservedQSO-galaxypairs. 0318-196 0.10415.9 0026+129 0.14215.7 < QSOdata*<— 0838+770 0.13116.3 References: (1)Monketal.(1986);(2)Palumbo,Tanzella-Nitti&Vettolani(1983);(3)ButadeVaucouleurs(4)Bottinelli 1048-090 0.34416.9 Bowen (1989);10)Thiswork;(11)Bergeron,D’Odorico&Kunth1987),andreferencestherein. Notes: (a)Stockton(1979)suggestsz-either0.228or0.346poor-qualitydata. 2308+098 0.43216.2 1219+047 0.09416.7 1543+489 0.40016.1 1341+258 0.08715.9 1219+755 0.07015.6 1211+143 0.08515.8 1411+442 0.08915.0 1327-206 1.16917.7 et al.1984;(5)Thuan&Seitzer(1979);(6)Stockton1979;(7)Bowen(1991);(8)Kirshner,OemlerSchechter(1978);(9) gal QSO © Royal Astronomical Society • Provided by the NASA Astrophysics Data System B ZWG 219.061 0026+1304 1341+2555 NGC 1300 UGC 4527 NGC 4319 NGC 4303 1327-2041 UGC 9105 IC 3061 Anon 2 Anon 1 Galaxy Anon 1 Anon 1 Anon 2 Dwarf (Irr)•0.5 Sab barred1.33.0 Spiral(Irr) •0.6: SBb(s)I.2 1.56.0 -1 — Interveninggalaxydata► Sc(s)1.2 1.16.0 Spiral 1.40.4 Spiral Spiral 4:0.4: Spiral 3.10.3 Spiral 1.20.3 Type R25(')(kms)Ref. Sc 4.11.6 2.4 0.5 ••• 0.1: 1 0.1 Additional sight-lines QSO-galaxy sample £>(0)25 V 0.9 @ l 2gal =0.1255 ¿gal =0.1726 ¿gal =0.075 ¿gal =0.076 ¿gal =0.0194 ¿gal =0.0350 2i =0.088 ¿gal =0.0180 field of2308+098,RandD(0)aremeasuredfromthe contour mapofGehrenetal.(1984). ga from methodswhichdonotrelyoncosmologicalpara- few existingvaluesofD,thedistancegalaxyobtained galaxy fromtheQSOonplaneofskyinarcminand kpc isgivenincolumns10and11.Incolumn12welistthe galaxy, or,forlargevelocities,itsredshift.Thereferences NGC 1300,andbotharequotedincolumn12.Finally, meters, takenfromthereferencesincolumn14;twovalues these valuesareUstedincolumn9.Theseparationofthe tan(p/60), wheresisinkpc,DMpc,andparcmin. column 13givesthetrigonometricseparation,5=1000D of DhavebeenmeasuredforbothNGC4303and discuss eachofthesetwocategories inturn. another dealingwithafewadditionallines-of-sight.Wenow 2525 We haveobservednineQSOs withlines-of-sightpassing sample ofobjectswhichsatisfycriteria(1)above,and Three ofthese havebeenobservedbefore; 1048-090was within 45h~kpcofforeground, low-redshiftgalaxies. 2.1.2 Finalsample In column8wegivetheheliocentricvelocity,V,of Table 1isdividedintotwosections,onecontainingthe Q 1555 1590 2263 1589 1394 721 a 10 10 11 2 5 6 6 2 1 9 8 6 7 2 9 Interstellar Caitabsorption147 _1 0.43 0.38 0.77 0.15 0.63 1.40 11.5 9.6 5.7 2.3 4.7 0.7 1.8 8.3 6.9 (') (/ikpc)(Mpc)(kpc)Ref. < QSO-galaxyseparations► p Ds 470 242 44 26 39 45 22 30 82 75 18 10 5 3 9.8-17.1 27-483,4 8.1-12.9 11-183,4 27 53 19 91MNRAS.249. .145B l l 148 D.V.Bowenetal. equivalent widthsseenalongsight-linesthroughtheGalactic tion toa2alimitof240mÀ,somewhatlargerthanthe originally observedbyMYJ,whodetectednoCanabsorp- halo. Both1219+047and0318-196wereoriginally to detectCanabsorption2alimitsofapproximately100 pairs, wemayalsoinclude3C232andNGC3067,originally observed withtheintentionofimprovingonexisting extended galacticdiscsaswellhaloes,theywerere- low inclinations,andcanthereforebeusedasprobesof excellent examplesofquasarsplacedbehindgalaxieswith and 150mÂ,respectively.Sinceboththeseobjectsare studied byBothun,Margon&Balick(1984),whoalsofailed the finalsamplehadabsorptionnotbeenknownin have beenobservedaspartofoursurveyandincludedin equivalent-width limits. observed byBoksenberg&Sargent(1978).Thispairwould advance. a separatepaper(Bowenetal.1991). from thesight-lineof1411+442,measurementstheirred- included inthispaperasprobesofGalacticCan. Several sight-linesobserveddonotsatisfycriteria(1)butare ( =Mrk205)andNGC4319,hasbeendiscussedindetail not thenearestgalaxytosight-linetowards1211+143.If shifts, madeaftertheabsorption-lineobservationsshowed 2.1.3 Additionalsight-lines field isrichingalaxies,andtheclosestgalaxyappearstobe for theneareroftwogalaxies,UGC9105.Further, from thequasarline-of-sightisgreaterthan200kpc.This that thelinearseparationsareinfactlarge,over240h~kpc found inBowen(1989). Monk eta/,whicharerelevanttothissurvey,aswella IC 3061,lyingbehindtheVirgoCluster,withaseparationof the galaxyisamemberofVirgoCluster,itsseparation more thoroughdescriptionofallthepairsinvolved,canbe contrary totheentrybyMonketal.(1986),NGC4216is satisfy thesamplecriteria. 15 h~kpc.However,bothNGC4216andIC3061failto us (MVP)usingtheRGOSpectrographandIPCSon However, observationsoftheCanlinesweretakenbyone D’Odorico &Kunth(1987),andBergeron(1984). of 1327-206hasalreadybeennotedbyBergeron, by theseauthors.However,sincetheBmagnitudeof D’Odorico &Kunth,butalsotoobservetheabsorption therefore excludedfromthefinal sample. complex ataresolutionhigherthanthe3.0ÂFWHMused QSO is17.7,thispairfailstosatisfycriterion(1),and allows usnotonlytoconfirmthedetectionbyBergeron, 3.9-m Anglo-AustralianTelescope(AAT)atSidingSpring Observatory, Australia.Aresolutionof0.6ÀFWHM between 1986and1988, with eitherthe2.5-mIsaac The spectroscopicdatapresented herewereobtained Newton Telescope (INT),partofthegroup of telescopesat 2.2 Observationsanddatareduction In drawingtogetheracompletesampleofQSO-galaxy Despite thesmallangularseparationoftwogalaxies One oftheQSO-galaxypairsinTable1,1219+755 Other errorsinthedetailsofQSO-galaxypairsgivenby The existenceofCanandNaiabsorptioninthespectrum © Royal Astronomical Society • Provided by the NASA Astrophysics Data System l The quotedinstrumentalresolutionincolumn7isbasedon or theAAT.ThejournalofobservationsisgiveninTable2. the ObservatoriodelRoquedelosMuchachosonLaPalma, were madewitheithertheIntermediateDispersionSpectro- the FWHMofemissionlinescomparison-lampspectra, AAT; thedetectorwasImagePhotonCountingSystem graph (IDS)ontheINTorRGOSpectrograph reduced inthesamewayasdata.Allobservations by STARLINK,theUKnetworkofVAXcomputersused routines withinfígaroorspica,softwarepackagessupported (IPCS) inallcases.Thedatareductionwasperformedusing this survey,sincethenon-detectionofabsorptionlinesmust the Britishastronomicalcommunity. not beduetotheincorrectmanagementofdatafrom involved isgivenbyBowen(1989).Webrieflyoutlinethe separate runs,andafulldescriptionoftheprocedures to between1500and2000s,weresandwiched steps below. Thorium-Argon orIron-Argonhollow-cathodelamps,pro- small driftsintheinstrumentation,integrationswerelimited from thegranularityofIPCSwasreducedbyvarying viding areferenceemission-linespectrum.Systematicnoise position oftheQSOalongslitspectrograph-and from thesamelocationandusedtowavelengthcalibrate A correspondingreference-lampspectrumwasextracted were locatedandextractedtoformaone-dimensionalimage. hence thedetector-betweensuccessiveintegrations.The January 12and14,toalltheobservationsof ing calibrationframeswereco-added.Finally,thedata pixel sizesone-quarteroftheoriginalsize.Aftersubtracting trum wasreducedtothesamelinearwavelengthscale,with object spectra(lyingatdifferentpositionsonthedetector) 100-200 sexposuresofeitherCopper-Argon, tion tomaximizethesignal-to-noiseratio. re-binned intowavelengthbinsone-halfofthefinalresolu- the skyspectrum,eachofobjectframesandcorrespond- data. Aftercorrectingtoaheliocentricrestframe,eachspec- tion oftheobjectandskydata.Suchamethodreduces were wavelengthcalibratedandre-binnedbeforetheextrac- applied tothedatafor0318-196obtainedon1988 necessity ofcalibratingalltheextractedobjectandsky spectra individually. uniformities inthephotometricresponseofdetector,as from ~38(1219+755)to~9(1327-206)perpixel,and this sourceofnoisewasalwaysreducedtoalevelmuch observing runs,theywereseldomusedtocorrectfornon- 1048 -090.Forthese,alltheindividualsectionsofanimage were inexcessof30000sformostobjects. We haveobservednineQSOs withprojectedseparationsof resolutions of0.5to1.4AFWHM.Totalintegrationtimes smaller thanthephotonnoiseofdata. between 3and45h~kpc from low-redshift,foreground galaxies, downto2aequivalent-width limitsofbetween38 3 RESULTS and 164mÂ(^ 100mÀforeightoftheobjects). Wepresent The accuracyofthedatareductionisobviouslycrucialto To preservetheresolutionwhichmaybedegradedby A variationofthis‘one-dimensional’reductionwas Though IPCSflat-fieldsweretakenduringmostofthe The finalQSOspectrahavesignal-to-noiseratiosranging 19 91MNRAS.249. .145B 0026+129 0318-196 0838+770 1048-090 Table 2.Journalofobservations. 1219+755 1219+047 1211+143 1327-206 1341+258 1411+442 1543+489 2308+098 QSO 1987 Sep16 1987 Sep17 1987 Dec13 1987 Sep18 1988 Jan14 1988 Jan13 1988 Jan12 1986 Feb17 1986 Feb20 1986 May28 1988 Feb27 1988 Feb26 1987 Apr26 1987 Apr24 1988 Jan14 1988 Jan13 1988 Jan12 1987 Feb15 1987 Feb15 1986 Feb17 1987 Feb19 1987 Feb15 1982 Mar23 1987 Feb19 1986 Feb20 1986 Feb18 1987 Apr24 1986 May30 1986 May29 1986 May28 1986 May30 1986 May29 1986 May28 1987 Apr26 1987 Jul28 1987 Apr23 1987 Jul31 1987 Aug03 1987 Sep17 1987 Sep18 Date Royal Astronomical Society •Provided by theNASA Astrophysics Data System UT Telescope CameraGrating AAT AAT AAT AAT AAT AAT AAT AAT AAT INT INT INT INT INT INT INT AAT INT INT INT AAT INT INT INT INT AAT INT INT INT INT INT INT INT INT INT INT INT INT INT INT 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 235mm 82cm 82cm 82cm 82cm 82cm 82cm 25cm 25cm 82cm 82cm 82cm 82cm 2400B 2400B 2400B 2400B 2400B 2400B 2400B 2400B 2400B 2400B 2400B 2400B 1200B 1200B 2400B 1200B 2400B 1200B 1200B 1200B 1200B 1200B 2400B 1200B 1200B 2400B 2400B 2400B 1200B 1200B 1200B 1200B 1200B 1200V 1200B 1200B 1200V 1200V 1800V 1800V Intergration ResolutionWavelength 5,800 2,000 4,000 10,000 4.000 9.500 12,000 4,300 13.000 11,000 8.000 9,600 6.500 8,360 15.500 10.000 11.000 11.900 8,000 10,000 6,000 14,000 10,000 14.000 4.000 7.250 10,460 4.000 6,000 6.000 8,750 10,000 10,000 8.500 5.000 7.900 10,400 3.250 10.000 11.900 Time (FWHM)Coverage (s) (Â)(Á) Interstellar Canabsorption149 0.58 0.58 0.54 0.54 0.58 0.56 0.55 0.55 0.54 0.55 0.55 0.55 0.55 0.55 0.72 0.72 0.67 0.67 0.72 0.57 0.57 0.57 0.57 0.57 0.65 0.65 0.65 0.66 0.65 0.61 0.56 0.75 0.75 0.6 1.3 1.1 1.3 1.3 1.1 1.4 3650-4160 3650-4160 3840-4140 3840-4140 3650-4160 3650-4160 3840-4140 3740-4240 3740-4240 4280-4590 4280-4590 3740-4240 4280-4590 3740-4240 3400-4430 3400-4430 3540-4060 3540-4060 3600-4090 3760-4240 3480-4480 3480-4480 3600-4090 3880-4153 3650-4140 3650-4140 3390-4430 3660-4150 3660-4150 3660-4150 3390-4430 3880-4380 3890-4390 3890-4390 4460-4770 4460-4770 4460-4770 3880-4380 4290-4980 4290-4980 19 91MNRAS.249. .145B 150 Figure 1.Spectraofthe11QSOs observedaspartofoursurvey,includingtheninewhichform unbiasedsample.WedetectCanabsorp- tion inonlyonecase, thatof1543+489,withequivalent widthsof62±22mÁand 82 ±22mÂfortheKand//line, respectively. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System • r-H -*-> "0) r—H • rH "0 te te a ; Q) 0 0 fí > CÖ 0 a U) 0 > 0 0 0 0 c (Ö 3850 390039504000 2 0 J,,LI-I-l-L.J__ 0 U^^Ii1 i I T 00838+770 01048-090 _ Expected positionofCaUKieHatz,[=0.1255 G ■ îtyi—^—r 4420 44404460 4480 Expected positionofCaIIK&HinUGC4527_ T Position ofGalacticCaIIKScH L Wavelength (Â) Wavelength (Â) Wavelength (Â) Wavelength (Â) - T !1—^^—r L i r T J 1 J i r 19 91MNRAS.249. .145B © Royal Astronomical Society • Provided by the NASA Astrophysics Data System •i—i • f-H ♦ pH -»J K w Q) Q) 0 CÖ > (/) fi fi 0 0 fi V) > 0 > 0 0 0 > 0 0 0 3850 390039504000 3850 0 -II 0 3900 39504000 4050 — "i ri| i r I 'I Q1211+143 Q1219+047 i 1I Q1341+258 I 1 Galactic CaIIfC&H 3900 39504000 Position of L Position ofGalacticCaIIfC&H Position ofGalacticCaII/CácH Figure 1-continued Wavelength (Â) Wavelength (Â) Wavelength (Â) i I Wavelength (Â) TT TTT Ca IIK&HinNGC4303 Ca IIK&Hin1341+2555 Expected positionof Expected positionof Ca IIAT&HinIC3061 _ Expected positionof riy ( r TTT -L 1.]L _i_ lIL , i J TTT [0 II]inQSO 1 T 1111 I .1. TTT TT 4100 151 19 91MNRAS.249. .145B l 152 D.V.Bowenetal. the spectrainFig.1;alldatahavebeennormalizedto range coveredbytheobservations.However,weidentify most caseswherethedoubletUnesarewithinwavelength QSO continuum.WehavedetectedlocalGalacticCanin spectrum ofonlyonequasar,1543+489,whichshows Can absorptionduetotheinterveninggalaxiesin weak, unresolvedabsorption with W(K)=62±22mÀand to bedueananonymous galaxy 45h~kpcaway,the largest separationforanyof theknownCanabsorbing absorption yetseeninaQSO-galaxy pair.Thelinesappear of Can[W(i^)^38 mÀ]inthespectrum of1219+755 systems. Thisdetectionisinsharp contrastwiththeabsence X W(H) =82±22mÀatz 0.07489.Thisistheweakest A aabs © Royal Astronomical Society • Provided by the NASA Astrophysics Data System • pH • rH in !>> "Ó) rÇÔ • rH Ö CD H-> > CD Ö (D CD V) (D ¡> (D (D 0 0 "01411+442 n—^—I—^^—r T r\“jn-TTi -L ,1IJ...J-..1,L.1J.I..,Ll-J i I 01543+489 I 02308+098 Expected positionofCaIIJC&//atZd=0.1726 Position ofGalacticCaIIJC&:Jf,. 3900 397540504125 4200 42404280 4600 46404680 J ^L Ca IIJC&Habsorptionatz=0.0749_ abs 11 I . 1—[Oil][OUI] Figure 1-continued Wavelength (Â) Wavelength (A) Wavelength (Â) Ca IIJC&Hatz=0.076 gftl L Expected positionof - r J ^L i 1r 1 2 tinuum inanintegralnumber ofpixels,andoisthe ( ÔXisthepixelwidth,V widthofthelineatcon- normalized data. WethenquotevaluesofW ± e standard deviationinthecontinuum) measuredfromthe the measuredequivalentwidth,e,wehaveadoptedMYJ’s equivalent widths,orupperlimits.Incalculatingtheerroron estimate ( =Mrk205),whichlies~3-5h~kpcawayfromtheface- on spiralNGC4319,betweenthenucleusofgalaxyand £^=ôAVac, (2) its southernarm(Bowenetal1991). c L A w w L —ii^r ( In Table3welistourmeasurementsoftheCanHandK Ca IIJC&HinUGC9105_ Expected positionof_ in QSO 1 J_ IL J ^ _ i 19 91MNRAS.249. .145B !2 -1 2 instrumental profile(FWHM),AA,thenNisgivenby If weassumethatthelinesaretryingtodetecthavesome intrinsic FWHM,AA,whichisthenconvolvedwiththe are givenby based onBoksenberg&Sargent’sobservationsof3C232, ^ _2'/AA¡+AAgi(lzJ normal, undisturbedgalaxies.Similarly,theinterstellarlines through NGC3067to3C232maynotbetypicalofmore M83. However,asexplainedinSection1,thesight-line and onJenkinsetalls(1984)observationsofSN1983Nin to thediscandhaloofourownGalaxyalongsight-line tion arisinginthehaloesofexternalgalaxies,andforthatdue limits toAf(Can) assumingthattheCanK line isoptically feel thatthe2alimitsderivedbyMYJassumingAA==1.2À km s)forCanformedinthehaloesofexternalgalaxies, derivation ofCancolumn densities, Af(Caii),fromthe novae morecommonlyshowmuchweakerandnarrower in SN1983Nareunusuallystrong;otherextragalacticsuper- sampled. Forcomparison,MYJassumedAA=1.2Â(90 2o=2ôPNo. (3) absorption linesfound.Thus in Table4wecalculatelower width introducedbytheplacementofcontinuum,e(in worst, ejW«3percent. to normalizethedataisfitted totheQSOcontinuum)is,at this casearesultoftheinaccuracy withwhichthesplineused are somewhatconservative.Theerrorintheequivalent Can absorption(Bowenetal,inpreparation).Therefore,we T gal ag gal gal wtc c A The 2aequivalent-widthlimitsquotedinTable3,2a, We adoptAA=0.6Â(45kms~^bothfortheabsorp- Our dataisofinsufficientresolution topermitanaccurate w gal © Royal Astronomical Society • Provided by the NASA Astrophysics Data System ÓA Table 3.Canabsorptionlineequivalentwidthsandlimits. 0026+129 0838+770 0318-196 2308+098 1219+047 1048-090 1341+258 1219+755 1543+489 1211+143 1411+442 1327-206 QSO 2a wW\(K)W\(H) (mÂ) (niÂ) 82 46 108 38 56 72 144 48 78 170 <— GalacticCaII—► not observed not observed 216+25 104+20 411+19 245+19 194+46 <108 151+35 102+26 104+22 <56 < 144 144+30 85+25 201+37 102+3174<74 265+71 <170164595+91213±690.01814+0.00007 221+21 97+1942<42 Additional sight-lines QSO-galaxy sample 22kms". absorber; upperlimitsarecalculated fromtheCanKline 0318-196 0026+129 0838+770 2308+098 1219+047 1048-090 1341+258 1219+755 1327-206 >2.8±0.8 >6.3 ±1.0 1543+489 1211+143 >2.3±0.2<0.7 1411+442 >2.1±0.4 < 2.3 QSO <62 62+22 <46 <108 <48 <38 <164 <68 <84 82+22 <108 <62 <46 <164 <68 <48 <38 <84 (mÂ) 2rs ab 12 Galactic CaII (XIO cm') a Additional sight-lines > 2.1±0.5 > 1.6±0.4 > 2.1±0.3 > 4.4±0.2 > 2.3±0.3 > 1.5±0.3 iV(Ca II) Interstellar Cauabsorption153 QS O-galaxysample < 81 0.07489 +0.00005 Extragalactic CaII 12-2 (xlO cm) a > 0.66±0.02 l\T(Ca II) < 150 < 1.5 < 0.6 < 1.8 < 0.8 < 3.7 < 0.8 < 14 19 91MNRAS.249. .145B =-1 l 154 D.V.Bowenetal. the valueof2oassumingadopplerparameter>2 thin. Wherenolinesarefound,wequoteanupperlimitfrom just onebroadKcomponentcentredat km s"Savalueconsistentwiththesmallestvaluesofbfound measurements areingoodagreementwithz=0.0179and FWHM, andequivalentwidthW{K)=595±91mÁ.These the galaxyESO1327-2041,inspectrumof206 three ofourlines-of-sight,deducedfrom21-cmemission in high-resolutionstudiesofGalacticclouds(e.g.Albert measurements byElvis,Lockman&Wilkes(1989), zbs 0.0181±0.0001,withawidthof«110kms are listedinthefinalcolumnofthattable. assuming aspintemperatureof250K.TheerrorinN(¥Li)is (1987). Evenwithourhigherresolution,weappeartodetect (Fig. 2)originallyreportedbyBergeron,D’Odorico&Kunth 1983; Crawford,Barlow&Blades1989). w Table 5.GalacticA(Can)/N(Hi). 0026+129 >1.6±0.44.93.30.8 abs X a 1219+755 >4.4±0.2 1211+143 >2.3±0.2 ~5 percent.ThecorrespondingvaluesofAf(Caii)/7V(Hi) Figure 2.AATSpectrumof1327 -206confirmingtheabsorptionbyCaninextendedarmof 1327 -2041,adisturbedgalaxywhichlies only 10h~kpcaway fromtheQSOline-of-sight. 1209 In Table5welistgalacticN{Hi)columndensitiesfor Finally, weconfirmtheexistenceofCanabsorptionby QSO (xlOcm-)cm“(xlO" © Royal Astronomical Society • Provided by the NASA Astrophysics Data System iV(Ca II)iV(HI)i\T(CaII)/iV(H 4.9 2.7 2.8 > 8.2±0.7 > 16±0.7 Wavelength (Â) l Kunth. weakest yetdetected,andthisisconceivablyaconsequence known toexhibitCanabsorption.Also,thelinesare ground galaxy(45h~kpc)isthelargestofallpairs ground galaxy. of thelargeseparationbetween1543+489andfore- photometric standardstarswerealsotaken,thoughcon- the framesbyanormalizedflat-field.Calibrationof an RCACCD.Thereductionofthedatafollowed CCD imagesofthefieldatprimefocusINT,using ditions duringthenightweredescribedasvariable.InFig.3 The projectedseparationbetween1543+489andthefore- 4 DISCUSSION contour plot,whichshowstheQSOandtwogalaxies we presentthesumoffive400sRexposuresinforma standard procedureofsubtractingabiasvalueanddividing listed inTable1.Theimagescaleis0.74arcsecpixel"^ contour levelswerechosentohighlightintensitiesjustabove 4.1 Absorptionin1543+489 the sky.Galaxy1isneareroftwogalaxiesto barred spiralwithtightlyboundarms,akintoanSba(s),and W(i£)«500 mAdeterminedbyBergeron,D’Odorico& is nearlyface-on.TheoffsetsofthesegalaxiesfromtheQSO, tion ofabout70°,calculatedfromitsaxialratio.Galaxy2isa quasar line-of-sight,and,ifaninclinedspiral,hasinclina- also taken,weareabletolistbothVandRintegratedmagni- sponding angularseparations.Becausea400sVframewas ÀRA andADec.,aregiveninTable6,alongwiththecorre- A To examinethissystemmoreclosely,wehaveobtained 19 91MNRAS.249. .145B -1-1 l l1 l l 1 tudes inTable6,alongwiththecorrespondingabsolute redshift ofthegalaxyandthatCanabsorptionis spectrum of1543+489?Thegoodagreementbetweenthe from theQSOline-of-sight)byasecondgalaxywhichlies18 the spectrumof2020-370isthatabsorptionoccursin certainly suggestive,butthelargeprojectedseparationisa magnitudes for//=100kmsMpcandq0. being membersofthesmallgroupKlemola31.However,in material whichisdrawnoutofthenearestgalaxy(8h~kpc cause forconcern.OneexplanationtheCanlinesseenin Figure 3.Contourplotoffive400sRexposuresthefieldaround1543+489,obtainedatprimefocusINTwith0.9 arcsec the caseof1543+489,twogalaxiesinFig.3areat a faint objectclosertothequasarline-of-sightonly6arcsecaway,labelledhereasObjectA.IfAisatsameredshiftabsorption seeing. Northistothetopandeastright.TheabsorptionfeatureseeninspectrumofQSOcanbeattributedgalaxy 1 whichis nor isthereanyevidenceforaninteractinggroup.Inthe much largerseparationthanthoseinthefieldof2020—370, 45 h~kpcaway,or(lesslikely)togalaxy2whichis82/rfromthequasarline-of-sight.Thepossibilityremainsthatabsorption arises ina we showthatthestrengthofabsorptionlinesseenin absorption bysuchaclassofobject. system, itsseparationis6h~kpc,andmagnitudeequalto—16.9inR.Thegalaxywouldthenbeadwarfgalaxy,thefirstexample of second paperofthisseries(Bowen1991,hereafterPaperII) h~ kpcway(Carilli&vanGorkom1987),bothgalaxies harder tojustifyforgalaxy1in thefieldof1543+489,since galaxy. Wealsoshowthatthis explanationisconsiderably absorption occurswithintheinclineddiscofnearer 2020-370 canbeaccountedforsimplybyassumingthat the diameterofdiscwould needtobe^105/z"kpc. 0 candidate -labelled ObjectAinFig.3-isindeed visible.It galaxy atthesameredshiftas galaxies 1and2,butatamuch smaller separationfromthe quasarsight-line.Sucha Is galaxy1responsiblefortheabsorptionseenin An alternativeexplanationis thatthereexistsathird o © Royal Astronomical Society • Provided by the NASA Astrophysics Data System 1543+489 a1b c l 1 Object A+0.6 Galaxy 1-31 Galaxy 2-38 For //=100kmsMpc*,q0.Assuminganextinction Table 6.Objectsinthefieldof1543+489. coefficient of0.1mag.Assumingaredshiftz=0.075. has aseparationof6arcsecfromtheline-of-sight,orh~ kpc ataredshiftof0.075.Theobjectisclosetospherical, A, whichmaybeaGalactic star, oragalaxyatsomeother and faint,withVRmagnitudesof19.921.3, respectively. NoredshiftmeasurementisavailableforObject redshift. However,iftheobject isatz=0.075,itsabsolute would thenbethefirstexample ofabsorptionbysuchaclass characteristic of¿/uw//galaxies (e.g.Binggeli1987)andthis magnitudes ofM=-15.5 and M^=-16.9wouldbe would thenhave actedasthe‘markers’of group.Clearly, of galaxy.Interestingly,thebrighter spiralgalaxiesinthefield 0 abs v Quasar 0 Object ("){h-kpc)R ARA ADECp +35 -74 -6 0 Interstellar Caiiabsorption155 46 84 0 6 c 6 45 82 0 c 16.1 -24.816.8 15.9 -20.916.9 16.5 -20.417.5 19.9 -16.921.3-15.5 a M fi ha V M v -19.9 -19.4 -24.0 19 91MNRAS.249. .145B l a In Table7wehavecompiledanunbiasedsampleof Bothun, Margon&Balick(1984)andfromthiswork.The have beenreported,regardlessofthesuccessindetecting this issuewillberesolvedonlybymeasuringtheredshiftof Boksenberg &Sargent(1978)isincludedinthesamplefor QSO-galaxy pairs,asetinwhichapparentlyallobservations 4.2 Thecross-sectionofgalaxiesinCan By expressingtheseparationinthisway,however,weare the galaxy,normalizedto11h~kpc,Holmbergradius the reasonsgiveninSection2.1.2.Thepairseparation absorption. TherelevantdataweretakenfromMYJ, Object A. 156 D.V.Bowenetal. Mg iiabsorbersderivedfromtheabsorption-linestatistics. of anL*galaxy.Thisallowscomparisonwiththehalosizes column 3,PiisthedistancebetweenQSOsight-lineand assuming thatthesizeofhaloisindependent 0506-162 0318-196 0026+129 2308+098 0955+326 0838+770 3C 232(=0955+326)-NGC3067pairobservedby 1302-102 1246-057 1048-090 1219+755 Table 7.CanabsorptionasafunctionofQSO-galaxyseparation. 2020-370 Klemola31A0.71.1: 1302-102 1355-416 1543+489 1341+258 1219+047 0446-208 Anonatz=0.0671.02.7: 0248+430 Anonatzi=0.0520.91: 0151+045 IC17461.3 2.3 0104+318 Anonatz=0.1121.31.2 1246-057 1103-006 1211+143 1327-206 1327-20410.92: 1411+442 Sum oftwocomponents.References: (1)thiswork;(2)Boksenberg Junkkarinen &Womble 1990. Boksenberg etal.1980;(6)Womble etal.1990;(7)Blades, 1? Hunstead &Murdoch1981;(8) Stockeetal.1984,1985;(9) & Sargent1978;(3)Bothun,Margon &Balick1984;(4)MYJ;(5) gal ga gai QSO Galaxy Anon at2i=0.094 Anon atzi=0.126 Anon at2i=0.173 Anon at2i=0.076 NGC 4697 NGC 4303 NGC 4319 Anon atzi=0.146 NGC 5408 NGC 1300 0026+1304 NGC 3067 UGC 4527 IC 3061 1341+2555 NGC 4731 NGC 3521 NGC 1796 UGC 9105 ga ga ga ga ga © Royal Astronomical Society • Provided by the NASA Astrophysics Data System Additional QSO-galaxypairs QSO-galaxy pairsample 22.0 13.5 4.2 4.0 4.7 4.1 3.7 3.5 0.5 2.7 2.4 2.0 0.7 0.5 5.7 5.4 9.0 6.8 1.6 4.7 4.7 2p/n(0) 3.3 8.7 3.0 9.2 0.5 23 54 9.0 28.5 33.0 12 1.6 1.9 13.0 14.4 18.4 14 25 a 54+22 W{K) < 93 < 42 <170 < 140 < 60 < 70 430+40 (mÂ) < 140 < 72 < 108 < 140 < 68 < 48 < 100 < 62 < 84 < 46 < 38 350+80 579+85 X 960+250 1600+234 < 200 < 100 0 % l ^ 2.5 ï more appropriatelybeexpressedintermsofthegalaxy’s galaxy’s opticaldimensions.If,ontheotherhand,sizeof the haloscaleswithgalaxyluminosity,separationshould optical radius.ThereforewealsolistinTable7the unbiased samplearelistedinthebottomhalfofTable7.The introduces someerror,however,asthemeasurementsof QSO-galaxy separationinunitsof2p¡D(0)[wherepand variation ofW(K)withPnisshowninFig.4,while5 £>(0)25 aredefinedinSection2.1.1].Thisnormalization £)(0) canbequiteuncertain. OÛ ? additional sight-lines.Apartfrom1543+489,allcasesof those observedinthepositivedetections. members ofthesampleinTable7,whileopencirclesdenote Figure 4.Plotoflog(p/l1kpc),theQSO-galaxyprojectedsepara- do notshowabsorption,despiteequivalent-widthlimitswellbelow Note thattherearetwocasesofsight-lineswithinthisvaluewhich absorption areconfinedtowithin11h~kpcofthegalacticcentres. tion inunitsof11kpc,versuslogW(K),theequivalentwidth cases ofsight-lineswithinthisvalue whichdonotshowabsorption, confined towithin~1and3 D{0)/2,orabout0.8of2.3 Can Kabsorptionline.Shadedcirclesrefertopairswhichare Figures. Plotoflog[2p/£>(0)2],whereZ)(0)5isthegalaxy’s as inFig.4.Apartfrom1543+ 489,allcasesofabsorptionare optical diameter,versuslogW(K ). Symbolshavethesamemeaning 15 detections. Holmberg radiiofthegalacticcentres. However,thereareseveral X even toequivalent-widthlimits well belowthoseofthepositive 25 3 2- X 25 52 X S 00 ' 2.5- 3.5 1.5 Additional QSO-galaxypairswhicharenotpartofthe 3.5 1.5 -4 3 3 - n i1\ n—i—r—i—i—i—i—i—i—i—r—i—r _l 1JIL_ 0 .51 : î l .I 4 1.Ql Log p(11kpc) 1543+489-- I i Log 2p/D(0) 25 . I 1543+489 .5 O Non-surveyObjects • SurveyObjects sr I l O Non-surveyObjects • SurveyObjects l —r ~\—i—i—r I 1.5 19 91MNRAS.249. .145B l -2 20- l l 1/2 by opencircles.Theerrorbarsaretheequivalent-width errors UstedinTable7. sight aredesignatedbyfilledcircles,non-samplesight-lines a plotofW{K)asfunction2p/D{0).Samplelines-of- profiles ofNGCgalaxies,wecanestimatethattheHolmberg only within11h~kpcofagalaxy,orthreetimes with equivalentwidths>0.6Â,asdiscussedinSection1. radius, R,isroughly1.3timestheradiusat/¿=25.0mag However, thereareseveralexamplesofnoabsorptionwithin and 2.3R.Thisisconsistentwithhalocross-sectionsof~ arcsec. Henceabsorptionoccurswithinapproximately0.8 £>(0)25/2. FromBoronson’s(1981)workonthebrightness most vividexample.Forinstance,forpairswith2p/£>(0)25 2.3 R,ofwhichtheline-of-sighttowardsMrk205is 2.3 RrequiredtoexplaintheincidenceofMgnabsorption mÀ. Again,ifwetakeaUthepairswithp<1.3,fivehave where H1columndensitieshavebeenmeasuredalong considering individualpairswhichdoshowabsorption,we to theequivalent-widthlimitsreachedinthissurvey.By around low-redshiftgalaxiesishighlyinhomogeneousatleast X25 found, suggestingthatthestrongCanlinesareassociated the line-of-sight,valuesofA(Hi)>:10cmhavebeen quence oftidalinteractionsorgalaxymergers,fromthe see thatabsorptionoccurseitherfrommaterialwhichisin note here,anddiscussmorefullyinPaperII,thatthecases extended discsofhighlyinclinedgalaxies(PaperII).Wealso some waydisruptedfromthegalaxy,perhapsasaconse- uB H primarily withlargeH1columndensities. u u exclude thepossibilityoflargerMgnhaloeswithhigher u low- andintermediate-redshifts.TheMgnhalodimensions difference inthedistributionofmetalsaroundgalaxiesat covering factors,andhencewhetherthereisanysignificant W(K)> 350mÂ,butthreehave<200mÀ. with unitcoveringfactors,andthatallgalaxiesare derived fromthesurveystatisticsassumesphericalhaloes < 3.0,fivehaveW{K)>350mA,but20 found hereforCa11,thentherequiredhaloradiiincreasesby £(£<1), oftheMgiiabsorbinggalaxiesislessthanone,as fractions ofacross-section,thenR*wouldincreaseby a factor of>3,andweshouldfindtheweakestMgnlinesat surrounded bysuchhaloes.However,ifthecoveringfactor, exclusively bydisruptedmaterialwhichcoveredsimilar Mg iiÂ2796lineisstrong(1.45À).Consideringthe distances >120h~kpc.Thismayinfactbethecasefor cross-section: iftheMg11absorptionlineswerecaused (Bergeron &Boissé1991),buttheequivalentwidthof to be140h~kpcawayfromtheQSOline-of-sight. tion discussedbyLanzetta&Bowen (1990),thereisastrong However, notonlyisthisseparationexceptionallylarge absorber towards0453-423,foundbyYannyetal.(1987) compared toalltheotherabsorbinggalaxiesdetectedsofar sight-line towards3C232coverslessthan0.1ofacircular £~. TheHiemittingmaterialbetweenNGC3067andthe suggested correlationofMg11 equivalentwidthwithsepara- possibility thattherealabsorber mayinfactbeanun- X detected objectmuchcloserto theQSO. X width limitsof theCa11andMgsurveyssample different and intermediate-redshiftsurveys isthattheequivalent- We conclude,therefore,thatthedistributionofCan With theexceptionof1543+489,absorptionisdetected The questionremains,however,whethertheseresults The realproblemincomparing theresultsfromlow- © Royal Astronomical Society • Provided by the NASA Astrophysics Data System l 1 column densities.Weclearlyneedtoknowtheratioof A(Can)/7V(Mgii) atlowredshifts-itmaybethatweare mediate-redshift surveys.Itremainspossible,therefore,that given thesameMgncolumndensitiessampledbyinter- indeed surroundedbylargeMg11haloes.Itmaywellbethat mediate redshift,andthatatthepresentepochgalaxiesare there isnodifferencebetweenthegalaxiesatlowandinter- simply notobservingwithenoughsensitivitytodetectCan unseen halo. ‘unusual’, denserregionswhichexistwithinamorediffuse, In comparinghalosizesinMgnandCanatpresent at thedetectionlimitsofoursurveys,wecanonlydetect past epochs,wearehinderedbythefactthatthereispracti- redshift galaxies,andlittleonCanabsorptioninthe cally noinformationontheMg11distributioninvisible,low- 4.3 Concludingremarksandfuturework from clear(seePaperIIforasummaryofMgnabsorberswith have onlyrecentlybeenimagedandwhosepropertiesarefar intermediate-redshift Mgnsystemsarisingingalaxiesthat which areactivelyformingstars.Atintermediateredshiftson different picturesofgalacticabsorption:atlowredshifts,we known Canabsorption).Naively,weappeartoidentifytwo whose sizesbroadlyagreewiththoseinferredfromthe within disruptedenvironmentsorexclusivelymedia see (strong)Canabsorptiononlyouttodistancesof~11 the otherhand,weappeartobefindingMg11absorptionwell haloes. is real,orsimplyduetousingdifferentspeciesprobelow- of typicalvaluesfortheW(Can)/WMgn)ratioingalaxy covering factorofunity.Establishingwhetherthisdifference absorption-line statistics,whichassumesphericityanda away fromthestellarcomponentsofgalaxies,inhaloes and intermediate-redshiftgalaxies,willrequireaknowledge h~ kpcandwithcoveringfactorsmuchlessthan1,either lines-of-sight thathavebeenusedtosearchforCan,thus which itsuffers,HSTwillstillofferasignificantimprovement the presentepoch.Despitesphericalabberationfrom establishing thecomparativesizeofCa11andMghaloesat allow thecomparisonofMgnabsorptionalongsame that longerexposuresandahighersignal-to-noiseper However, thelossinthroughputandresolutionwillmean over IUEinitsabilitytodetectMgnabsorptiontheUV. Further studiesofCanabsorptionatlowredshiftshould the sizeofMgnhalobetweennowandredshifts~0.5. envisaged. Weshouldalsobeabletodiscernanyevolutionin spectrum willberequiredcomparedtothatpreviously be focussedontheimportanceofgalaxy-galaxyinteractions concentrate onpairswithseparationssmallerthanthe11 A in causingabsorbingmaterialtobedistributedoutthese absorption isseenbelowthislimit.Specialattentionshould limits. ACKNOWLEDGMENTS /T kpcdiscussed,toquantifytheregularitywithwhich We wouldliketothankthestaff oftheINTandAATfor their facilitiesandsupportduring thisprogramme,including DVB wouldlike tothankhiscollaboratorsfor theirguidance those whocarriedoutthe relevant serviceobservations. Access toTheHubbleSpaceTelescope(HST)willfinally Interstellar Ca11absorption157 19 91MNRAS.249. .145B REFERENCES Womble forbringinganobscurepapertohisattention,and Albert, C.E.,1983.Astrophys.J.,272,509. 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