A wide-field spectroscopic survey of the cluster of galaxies Cl0024+1654 I. The catalogue

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

Astronomy&Astrophysicsmanuscriptno.(willbeinsertedbyhandlater)

Awide- eldspectroscopicsurveyoftheclusterofgalaxies

Cl0024+1654

arXiv:astro-ph/0103123v1 7 Mar 2001

I.Thecatalogue

OliverCzoske1,Jean-PaulKneib1,Genevi`eveSoucail1,TerryJ.Bridges2

Jean-CharlesCuillandre4,5

12345

,YannickMellier3,5,and

ObservatoireMidi-Pyr´en´ees,UMR5572,14Av.EdouardBelin,31400Toulouse,FranceInstituteofAstronomy,MadingleyRoad,Cambridge,CB30HA,UKInstitutd’AstrophysiquedeParis,98bisBd.Arago,75014Paris,FranceCFHTCorporation,P.O.Box1597,Kamuela,Hawaii96743,USA

ObservatoiredeParis,DEMIRM,61Av.del’Observatoire,75014Paris,France

Receivedtoolate,Acceptedevenlater

Abstract.Wepresentthecatalogueofawide- eldCFHT/WHTspectroscopicsurveyofthelensingclusterCl0024+1654atz=0.395.Thiscataloguecontains618newspectra,ofwhich581haveidenti edredshifts.Addingredshiftsavailablefromtheliterature,the nalcataloguecontainsdatafor687objectswithredshiftsidenti edfor650ofthem.295galaxieshaveredshiftsintherange0.37<z<0.41,i.e.areclustermembersorlieintheimmediateneighbourhoodofthecluster.Theareacoveredbythesurveyis21×25arcmin2insize,correspondingto4×4.8h 2Mpc2attheclusterredshift.Thesurveyis45%completedowntoV=22overthewhole eldcovered;within3arcminoftheclustercentrethecompletenessexceeds80%atthesamemagnitude.Adetailedcompletenessanalysisispresented.Thecataloguegivesastrometricposition,redshift,VmagnitudeandV Icolour,aswellastheequivalentwidthsforanumberoflines.ApartfromtheclusterCl0024+1654itself,threeotherstructuresareidenti edinredshiftspace:agroupofgalaxiesatz=0.38,justinfrontofCl0024+1654andprobablyinteractingwithit,aclosepairofgroupsofgalaxiesatz～0.495andanoverdensityofgalaxiesatz～0.18withnoobviouscentre.Thespectroscopiccataloguewillbeusedtotracethethree-dimensionalstruc-tureoftheclusterCl0024+1654aswellasstudythephysicalpropertiesofthegalaxiesintheclusterandinitsenvironment.

Keywords.galaxies:clusters:Cl0024+1654–cosmology:observations–cosmology:large-scalestructureoftheUniverse

1.Introduction

Clustersofgalaxiesareincreasinglyviewednotassimpleisolatedandrelaxedsystemsbutasembeddedinandcon-nectedtothegenerallarge-scalestructureintheUniverse.Thisviewofclustersinalargercontexthasconsequencesfortheinterpretationofclustergalaxypopulations,clusterdynamicsandmassestimates.

Clustersofgalaxiesgrowbycontinuouslyaccretinggalaxiesandgroupsofgalaxiesfromthesurrounding eld,mostlyalong lamentarystructures.Intheprocess,galax-

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

2O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

iesistakingplace.Theadventofnewwide- eldCCDmosaiccamerasavailableonanumberoflargetelescopes(e.g.CFHT,CTIO,Subaru,ESO2.2m)makesitpossi-bletoobtainphotometricandmorphologicalinformationon1-10Mpcscalesaroundtheclustercentres.However,wide- eldinvestigationofclustersdemandsbothimag-ingandspectroscopicobservations.Individualspectraofgalaxiesdescribetheirspectralenergydistributionandprovidetheirredshift,whichisindispensabletoproduceacatalogueofclustermemberswithradialvelocityandinformationregardingtheirstellarcontentandstarfor-mationhistory.Atpresentthereisonlyalimitednumberofclusterswithmorethan～200spectroscopicallyiden-ti edmembergalaxies(e.g.Abrahametal.1996),andespeciallyathighredshift(z>～0.2)spectroscopicallywell-studiedclustersbecomeveryrare,mostlyduetothefactthatcontaminationby eldgalaxiesincreasesrapidlywithredshift.

Thefactthatclustersarenotisolatedsystemsalsoraisesquestionsconcerningthetraditionalwaysofesti-matingmassesofclustersofgalaxiesthroughdi erentmassestimators:gravitationallensinganalyses,kinemati-calanalysesfromredshiftsofclustermembergalaxiesandX-rayobservations.

Gravitationallensingissensitivetothetotalintegratedmassalongtheline-of-sightfromtheobservertothelensedsources,weightedbytheappropriatecombinationofangu-larsizedistancesbetweenobserver,lensandsource(e.g.Schneider,Ehlers&Falco1992,Bartelmann&Schneider2001).Inthepresenceofmassivestructuresotherthantheclusteralongthelineofsight,rgespectroscopicsurveysprovideadditionalinformationneededtocorrectlyinterpretthelensinganal-ysisinthiscase.Metzleretal.(2000)investigatethein u-enceofthepresenceof lamentsandgroupsofgalaxiesinthevicinityofaclusteronweaklensingestimatesoftheclustermassand ndthatsigni cantoverestimates(uptoafactor1.5to2)arepossibleandevenlikely.SimilarinvestigationswithcomparableresultswereconductedbyCenetal.(1997)andReblinskyetal.(1999).

Asimilarbiasshouldbeexpectedtoa ectmeasure-mentsofvelocitydispersions:ifforegroundorbackgroundgroupsofgalaxiesintheimmediateneighbourhoodoftheclusterareaddedintotheredshifthistogram,butarenotresolvedandrecognizedasseparateentities,theveloc-itydispersionoftheclusteritselfwillbeoverestimated.Generallyonly30to50membergalaxiesareusedtoestimatetheline-of-sightvelocitydispersion(andvirialclustermass;seee.g.thelargecompilationsofGirardietal.1998andGirardi&Mezzetti2000).Furthermore,themeasuredredshiftsaregenerallyconcentratedwithinarelativelysmallregionwithinaprojectedradiusof～500h 1kpcoftheclustercentre.Whereasonecanarguethatthesenumbersmightbesu cientforrelaxedclusterswithregularspatialandvelocitydistributions,thevari-ousderivedestimateswillcontainlargesystematicerrorsifunresolvedsubstructuresarepresent.Whatcanbeob-

tainedfromredshiftsurveysisagalaxynumberdensityweightedline-of-sightvelocitydispersionaveragedalongtheline-of-sight.Withasu cientlylargenumberofclus-termemberredshiftsitispossibletomeasurethevariationoftheline-of-sightvelocitydispersionwithprojecteddis-tancefromtheclustercentre(Carlbergetal.1997),butdeterminationofevenmoredetailedinformationonthedynamicalstatus(e.g.velocityanisotropypro le)ofaclusterrequiresaforbiddinglylargenumberofredshifts(e.g.Merritt1987).

Clearly,combininginformationcomingfromgravita-tionallensing(weakandstrong),theX-rayemissionfromthehotintra-clustergas,theSunyaev-Zeldoviche ectandthegalaxyvelocitydistributionisthebestwaytoarriveatsecuremassestimatesforclustersofgalaxies(seee.g.Castanderetal.2000).Thisisnowpossibleforseveralcases.Ofparticularinterestareclustersforwhichasig-ni cantdiscrepancybetweendi erentmassestimatesisfound.Onesuchclusteristhewell-knownlensingclus-terCl0024+16541.About100redshiftsofgalaxiesinthisclusterwereobtainedbyDressler&Gunn(1992)andDressleretal.(1999),resultinginavelocitydispersionofσ 1300kms 1,whichisconsistentwithmassestimatesderivedfromthespectaculararcsystemintheclustercentre(Kassiola,Kovner&Fort1992,Smailetal.1996,Tysonetal.1998,Broadhurstetal.2000).Cl0024+1654wasamongthe rstclustersinwhichacoherentshearsig-nalduetoweaklensingwasfound(Bonnetetal.1994).Acrudemassestimatefromthisanalysiswasconsistentwiththestronglensingandkinematicalestimates.Inaddi-tiontothesignalduetoCl0024+1654itself,Bonnetetal.(1994)alsofoundacoherentsignaltothenorth-eastoftheclustercentreinanareawherenoobviousgalaxyoverden-sitycouldbeseen.TheX-rayluminosityofCl0024+1654ontheotherhandisunusuallylowforaclusterofthisvelocitydispersion,andmassestimatesfromtheX-rayobservationsareafactoroftwotothreelowerthanthelensingandkinematicalestimates(Soucailetal.2000).

InordertobetterunderstandthedynamicsofCl0024+1654andhowitisembeddedinthesurroundinglarge-scalestructure,wehaveconductedawide- eldspec-troscopicsurveyattheCanada-France-HawaiiTelescope(CFHT)andtheWilliamHerschelTelescope(WHT)from1992to1996.Inthispaperwepresentthecatalogueofthegalaxiesobservedforthissurvey.Section2summa-rizesthephotometricandspectroscopicobservations.ThedatareductionandanalysisarepresentedinSection3.Section4discussessomeinterestingglobalresultsofthesurveyanddescribessomestructuresfoundintheredshiftdistributionthatarenotdirectlyrelatedtotheclusterCl0024+1654.AsummaryisgiveninSection5.Ade-tailedanalysisofthedynamicsoftheclusteritselfandits

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue3

environmentaswellasthespectralpropertiesofitsmem-bergalaxieswillbethe

subject

of

a

forthcoming

paper

(Czoskeetal.2001).

Throughoutthis paper1weuseaHubbleconstantH10=100h kms 1Mpc, M=1and 1Λ=0,whichgivesaphysicalscaleof3.195hkpcarcsec 1attheclusterredshift.

2.Observations2.1.Imaging

Wewillusephotometricresultsfromtwobroad-bandim-agesintheanalysisofthespectroscopicsurveypresentedinthispaper.

On26September1995,weobtainedanI-bandimageusingtheUH8kcamera(Luppino,Metzger&Miyazaki1995)onCFHT.TheI-bandimagewasreducedchipbychip,i.e.the nalresultisintheformofeightindividualimages,oneforeachchipofthecamera.The nalimageswereobtainedasthemeanof10exposuresof1200seach,usingsigmaclipping(2.5σabovethemeanleveland4σbelow)torejecthotpixelsandcosmicrayhits,andhaveverygoodseeingof0′′.7FWHM;however,thebackgroundismarredbystraylight,presumablyduetothebrightstar47Psc(V=5.1,spectraltypeM3)at～50′distancefromthecentreofCl0024+1654,althoughoutsidethe eldofviewoftheUH8k.TheI-bandphotometriccataloguewasobtainedfromtheindividuallystackedchipsusingtheSExtractorpackage(Bertin&Arnouts1996)withathresholdof1.5σandaminimumdetectionareaof5pix-els.Thecataloguecontainsmorethan4×1042objectsovera eldofabout28×28arcmin,thelimitingmagnitudeisI～24.Unlessotherwisenoted,weusetotalmagnitudesasgivenbySExtractor’sMAG

2

IRAFisdistributedbytheNationalOpticalAstronomyObservatories,whichareoperatedbytheAssociationofUniversitiesforResearchinAstronomy,Inc.,undercooper-ativeagreementwiththeNationalScienceFoundation.3

http://archive.stsci.edu/dss/

V<23.3(0.01forV<21.1).ThelimitingmagnitudeisV～25.

Inordertoobtaincolourinformationaperturemagni-tudesweremeasuredin14pixel(2′′.8)diameteraperturesfortheV-andI-bandimages.Thisdiameterissu cientlylargecomparedtotheseeingFWHMtoenclosemostofthelightfromtheobjectunderconsiderationandsmallenoughtoavoidcontaminationbyneighbouringobjectsincrowdedregionsliketheclustercentre.TheobjectswerethenmatchedupusingapolynomialtransformationoftheI-bandimagecoordinatesontothesystemoftheV-bandimage.Thecentresofthetwoimagescoincidetowithin40arcsec,sothattheoverlappingregioncoversvirtuallythewholeUH8k eld.NotethatthegapsfromtheIbandimageshowupinthecolour-magnitudecat-alogueaswell.Theresultingcolour-magnitudecataloguecontains～2.1×104objectswitherrorsonthecoloursofsmallerthan0.05forV<23.3(0.01forV<21.1).Star-galaxyclassi cationoverasub-regionofthecolour-magnitudeplane(asrelevantforthepresentpaper)willbedescribedinSect.3.5.

Amoredetaileddescriptionofthephotometriccat-alogue(includingstar-galaxyseparationoverthewholecolour-magnitudeplane)isgiveninMayenetal.(2001)whousethiscataloguetoinvestigatethedepletionofbackgroundgalaxiesduetothegravitationallense ectofCl0024.

2.2.Spectroscopy

Spectrawereobtainedusingmulti-slitspectroscopyduringthreeobservingrunsatCFHTandoneatWHT.Table1showstheobservinglog.

Candidatesforalltheruns(exceptforrun1)wereselectedfromaV-bandmosaicobtainedattheESONewTechnologyTelescope(NTT)on17/18October1993,withtheprimaryselectioncriterionbeingVNTT<23.Thesee-ingonthisimagewasratherpoor,～1′′.7FWHM.Inordertoreducecontaminationbystars,thepreparatoryshal-lowR-bandimageswerecarefullyexaminedduringalltheCFHTruns;forruns3and4,wetookadditionaladvan-tageoftheexcellentseeingofthedeepUH8kI-bandim-age.

AlltheCFHTobservationsweredonewiththeMulti-ObjectSpectrograph(MOS,LeF`evreetal.1994)withtheO300grism.ThecamerasusedduringeachrunandthecorrespondingpixelscalesanddispersionsarelistedinTable1.Twoto veexposurespermaskwereobtained,dependingonthemagnitudesoftheselectedobjectsineachmask.

Band-limiting lters,chosensuchthatprominentspec-tralfeatures(forinstancetheCaiH/Klinesbluewardofthe4000 Abreak)fallintothebandattheredshiftofinterest,allowstackingofseveralrowsofspectraononemask,thusincreasingthenumberofspectraobservableinagiventime.Thisstrategyhasbeensuccessfullyemployedbye.g.Yeeetal.(1996,2000).However,spectracovering

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

4O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.The

catalogue

Fig.1.22′×25′sectionoftheCFH12kV-bandimageshowingthedistributionoftheobjectsinourspectroscopicsample.ExpandedviewsofthemarkedregionsareshowninFigs.4a–4hasindicatedintheimage.Thecoordinatesgivenarerightascensionanddeclinationrelativetoα2000=00h26m35s.70,δ2000=17 09′43′′.06.alargerrangeofwavelengthsprovidemoresecurered-shiftdeterminationssincemoreabsorptionandemissionlinescanbetakenintoaccount.Thisisparticularlyim-portantinthepresenceofartifactscausedbyinsu cientremovalofcosmicrayhits.InthecaseofCl0024+1654at

breakroughlycoincideswiththez=0.395,the4000A

strongskyemissionline[Oi]λ5577,sothatinsu cientsubtractionoftheskylinemightcauseaproblemintheredshiftdeterminationifonlyalimitedwavelengthbandwereavailable.Also,coveringawidewavelengthrangeis

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue5

essentialinordertoderivespectraltypesforthegalaxiesandanalyseindetailthespectralpropertiesoftheclustermembers.Forthesereasonswedidnotuseband-limiting lters andtheusablewavelengthrangewastypically4500–8500A,dependingonsignal-to-noiseratioandthequalityoftheskysubtractionattheredendofthespectralrange,wheretheskyemissionisdominatedbymolecularbands.TheobservationsatWHTweremadewiththeLowDispersionSurveySpectrograph(LDSS-2,Allington-Smithetal.1994),themed/bluegrismandtheLoralLOR1detector.Theusablewavelengthrangewas4000–7500 A,somewhatbluerthanfortheMOSobservations.AlltheLDSS-2maskswerecoveredbytwoexposureseach.Weused1′′wideslitsthroughout,resultinginares-olutionof～13 A,exceptforrun1wheretheslitwidth

usedwas1′′

.5withacorrespondinglyworseresolutionof～20 A.

3.Datareductionandanalysis3.1.Reductionofspectroscopicdata

Thespectrawerereducedusingthesemiautomaticpack-agemultired(LeF`evreetal.1995)whichinturnusesstandardIraftasksandtreatseachslitseparately.Thespectralimageswerede-biasedand at- eldcorrectedinthestandardway.Alow-order(mostlylinear)polynomial ttotheskyemissioninthespatialdirectionwasthensubtractedforeachindividualexposure.Duringthe tmostofthecosmicrayhitsintheskyregionofthespec-tralimagesweretakencareofbyasigma-rejectional-gorithm(pixelswithdeviationsofmorethan±2σfromthe twererejectedbeforere tting);neverthelessinsuf- cientlyrejectedcosmicsoccasionallysurvivedthe ttoproducefakeabsorptionfeaturesintheobjectspectrum.Geometricdistortionscausethetruespatial/dispersiondirectionstodeviatefromtherow/columndirectionsoftheCCDchip,especiallyattheedgesofthe eld.Sincesky ttingwasdonerow-wise(column-wisefortheWHTdata),skyemissionlinestendtobeimperfectlysub-tracted.Isolatedemissionlines(inparticular[Oi]λ5577,whichroughlycoincideswiththe4000 AbreakforgalaxiesattheredshiftofCl0024+1654)couldsimplybemaskedforthesubsequentanalysisofthespectrum,buttheus-ablewavelengthrangeintheredwase ectivelylimitedbythemolecularbandemissionfromthesky.

Theindividualexposureswerethenaveragedintothe naltwo-dimensionalspectrum.Inthosecaseswheremorethantwoexposurespermaskwereavailable,thehighestpixelvaluewasrejected,thusaccountingforcosmicrayhits.Thesmallnumberofexposurespermaskmadecos-micrayrejectiondi cultandimperfect.Acosmicrayhitontheobjectspectrumresultedinafakeemissionfeature,ahitintheskyareainafakeabsorptionfea-ture.However,asarguedinSection3.2,cosmicsdonotingeneralin uencetheredshiftdetermination.Finally,variance-weightedone-dimensionalspectrawereextractedfromthecombinedspectralimages,wavelengthcalibrated

usinglampspectra(He/AratCFHT,Cu/AratWHT)

andapproximately ux-calibratedwithlong-slitspectrafromspectro-photometricstandardstars(listedinTable1).

Thewavelengthcalibrationspectrawereextractedus-ingastraighttrace(followingthecolumn/rowdirectionoftheCCD),unlikethecorrespondingobjectspectra,wherethetracefollowedthe exureintroducedbygeometriccameradistortions.Weveri edthatthiscausesonlyneg-ligibleerrorsbyre-calibratingseveralspectrawithstrong exurewithcalibrationspectraextractedusingthesametraceasfortheobjectspectra.

We nallyperformedacheckonthewavelengthcali-brationbyextractingthreespectrapermaskwithoutskysubtractionandmeasuringthepositionofprominentskylinesusingthecalibrationfromthelamps.FortheWHTmasksthisrevealedsystematicshifts,whichareduetothefactthatthelampspectrawerenottakenimmediatelybe-foreorafterthescienceexposures.Thepositioningofthemasksinthemaskholderwasthereforenotidenticaldur-inglampandscienceexposures.Thesesystematicshiftstranslateto～10 3intermsofredshiftandacorrectionforeachmaskwasappliedtoalltheredshiftsdeterminedfromthismask.Nosuchsystematice ectwasfoundfortheCFHTmasks.

SevenexamplespectraandtheV-bandimagesforthecorrespondingobjectsareshowninFig.2.

3.2.Redshiftdetermination

Sincealargefractionofthespectrainoursamplehaveratherlowsignal-to-noiseratio,wedecidedtoidentifyred-shiftsbyeye,whichisbetterat ndingrealabsorptionandemissionlinesamongstnoisethanautomaticredshiftiden-ti cationtechniques.Also,fakeemissionandabsorptionfeaturesduetocosmicscouldbeidenti edthiswaybysim-plycheckingtheoriginaltwo-dimensionalspectralimages.Allredshiftswereidenti edbyoneofus(OCforruns2-4,GSforrun1)andcheckedbyatleastoneothermemberoftheteam.Theredshifts(runs2-4only)giveninTable4carrya agwhichindicatesa(somewhatsubjective)levelofcon dencethattheredshiftidenti cationiscor-rect.“Secure/A”redshiftsweredeterminedfromspectrawhereemissionlinesand/orseveralabsorptionlinesareclearlyseen,“uncertain/D”redshiftsarebasedonaten-tativeidenti cationofasinglelineorpossiblyseveralweakabsorptionlines,and“probable/B”and“possible/C”in-dicateintermediatelevelsofcon dence.

Inordertoobtainamoreobjectiveestimateofthemeasurement(asopposedtoidenti cation)errorofourredshifts,weusedthecross-correlationtechniqueimple-mentedinthetaskxcsaointheIrafpackagervsao(Kurtz&Mink1998).Inallcases,theby-eyeredshiftidenti cationwasfedtoxcsaoastheinitialredshiftes-timateandtheallowedredshiftrangewasrestrictedtoabout±5%aroundthisredshift.Inthissense,xcsaowas

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

6O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

Table1.Logofthespectroscopicobservingruns.

124–27/08/92CFHT/MOSSAIC1O300224–27/08/95CFHT/MOSLoral-3O300312–15/09/96WHT/LDSS-2LOR1med/blue411–13/11/96CFHT/MOSSTIS-2O300-1allqualities

“secure/A”onlyRunsN(z1 z2)N2–2198.2—198.23–364.8—45.84–4

9

6.6

—

7

5.4

forcedtorecoverourredshiftidenti cationandweonlyusedxcsao’serrorestimate.

Forlargevaluesofthecorrelationparameter,R>3(Kurtz&Mink1998),we ndthatxcsaoreproducesourinputredshiftsverywell.Themeandeviationbetweenby-eyeredshiftandxcsaoredshiftis

24.5–7.5180.3774.31Feige11066.6–15.6150.3143.69Wolf134695.4–7.2150.3573.30HZ4

36.6–8.1210.4405.03Hiltner600

(z1 z2)betweentheobservationsis

consistentwithzero.

FinallywecompareinFig.3theredshiftsforthose54objectsthatwereobservedbothbyusandbyDressleretal.(1999).Forthemajorityoftheseobjectsthered-shiftmeasurementsagreeverywell,however,thereare veclearmisidenti cations,withredshiftdeviationofmorethan0.01;thesecasesarediscussedindetailinSect.3.4.Object523deviatesbymorethan3σifthe vemisidenti- cationsaredroppedfromthesample,soweexcludethisobjectaswell.Theremaining48commonobjectshaveameanredshiftdeviation

of

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

7

(a)

H/Hε

K

[OIII]

Hδ

HηHζGHγ

Hβ

(b)

skyHζHδ

G

HγHβ

MgI

KHHηHθ

(c)

[OIII]cr[OII]

Hβ

(d)

skyHδ

Hγ

cr

KH

G

Hβ

(e)cr

skybr

(f)

Hβ

br

MgI

G

cr

(g)

[OII]

[OIII]

sky

Hβ

Hη

Hε

Hγ

Hδ

Fig.2.Examplespectraandcorresponding15×15arcsec2sectionsfromtheCFH12kV-bandimage.ThecatalogueentriesfortheseobjectsarelistedatthetopofTable4.Spectra(a)and(d)arefromobservingrun2(CFHT),spectra(b),(c),(e)and(g)fromrun3(WHT),andspec-trum(f)isfromrun4(CFHT).Spectra(a),(b)and(c)areexamplesofspectrawith“secure/A”redshiftsbasedonalargenumberofemissionand/orabsorptionlines.Spectrum(d)isanexampleofa“probable/B”redshiftandspectrum (e)ofan“uncertain/D”redshift,basedonthe4000Abreakonly.Spectrum(f)isforthecentralgalaxyofthenortherngroupatz～0.495,discussedinSect.4.Spectrum(g), nally,isforaveryblueclustermembernearthecentreofCl0024+1654,showingalmostthecompleteBalmerseriesinemission.Cosmicrayhitsaremarked“cr”,skyemissionlinesby“sky”.Notethatthewavelengthrangesaredi erentineachpanel.equivalentwidthssothattheyarepositiveforemissionlines:NWλ=

intfi

i=1

fcwasestimatedas

themeanvaluewithintwowavelengthintervalsoneithersideoftheline;pixelswithvaluesmorethan3σawayfromthemeanlevelwereiterativelyrejectedinordertoavoidcosmicrayhitsinthecontinuumregion.Theautomaticmeasurementofthecontinuumlevelmakesitpossibletoestimateanerroronthecorrespondingequivalentwidths,thusallowinganassessmentofthedetectionsigni canceoftheline.ForthispurposewemodelthenoiseasPoisson-distributedphotonnoise.Thisallowsustorelatethevari-ancesonfiand

fc,S/N=

fc 2

=σ2

c/NcwhenaveragedoverNc

pixels.Addingtheerrorsduetofiand

N

2

(W+N(Wλ+Nint λ) λ+

int λ)2

λ

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

8O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

Table3.Wavelengthrangesforequivalentwidthmea-surements.Allthewavelengthsaregivenin A(“i/a”—interactiveplacementofcontinuumlevel).

[Oii][Oiii]HαHβHδbreakS/N372750076563486141034000—3713–37414997–50176556–65704851–48714088–4116

–

4050–42503653–3713

i/ai/ai/a4030–40823750–3950

–3741–3801

i/ai/ai/a4122–41704050–4250

–

BEST),from

CFH12kimage.

Column7:V Icolour,measuredin14pixel(2′′.8)diame-teraperturesfromtheCFH12k(V)andUH8k(I)images.OccasionallyImagnitudes(andhenceV Icolour)arenotavailableduetotheobjectfallingonagapbetweentwochipsoftheUH8k(seeSect.2.1).

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

9

Table 4. The catalogue. This table presents a selection from the sample, the full catalogue is available in electronic form at CDS. The rst seven entries correspond to the example spectra shown in Fig. 2. The next seven/six entries belong to the northern/southern groups at z～ 0.495, discussed in Sect. 4. Finally we list several objects in the vicinity of the dark structure detected by Bonnet, Mellier& Fort (1994). See the text for a description of the table contents.num O. Czoske et al.: Spectroscopic survey of Cl0024: I. The catalogue 531 221 80 625 103 540 378 209 315 519 537 546 562 567 51

3 528 556 579 580 610 518 542 544 552 563 566 576 ... R.A. 189.8 -117.1 -366.5 376.6 -323.9 206.2 3.9 -133.6 -34.2 175.1 199.7 216.7 240.2 251.0 169.4 184.6 230.6 268.7 271.4 332.6 175.0 209.8 211.3 226.9 240.6 246.2 262.0 ... Dec 414.9 150.3 -117.5 305.8 158.1 588.7 -5.6 596.3 559.5 558.2 599.4 589.7 531.6 545.7 393.7 374.3 271.1 353.6 363.7 387.9 255.1 261.6 243.4 245.0 256.7 279.9 260.8 ... z 0.3943 0.3938 0.3944 0.3900 0.3963 0.4907 0.3973 0.4892 0.4928 0.4912 0.4951 0.4877 0.4917 0.4980 0.5016 0.4969 0.4955 0.5000 0.4938 0.4939 0.0000 0.2981 0.1755 0.3935 0.3797 0.4000 0.3911 ... Q A A A B D A A A A A A C C A C A A B A B S A B A A A A ... V 21.70 20.46 23.46 21.41 21.88 21.03 22.58 22.48 22.28 21.32 21.37 21.81 20.23 20.30 22.98 22.24 23.47 23.57 21.94 22.45 21.78 22.34 19.98 23.02 20.56 21.49 21.86 ... V I 1.18 1.73 0.62 1.47 1.69 2.48— 1.20 1.68 2.35 2.39 2.33 1.24 1.58 1.87 2.12 2.35 2.04 2.28 2.16 3.07 0.97 1.39 1.09 1.61 1.63 1.77 ...[O ii] 23±3 77±15 12±2 78±5 33±2 8±1 10±2 10±2 21±4 1±2 3±2 14±4 6±2 20±3 31±11 53±8 8±1 ...[O iii] 6 109 48 6 9 19 ... Hα 12 ... Hβ 4 23 32 10 4 3 ... Hδ 4±1 3±1 4±2 5±1 5±2 3±1 5±1 ... 4000 A 1.1 1.8 1.1 1.4 1.7 1.7 1.1 1.4 1.5 1.8 1.4 1.2 1.1 1.2 1.4 1.7 1.5 1.5 1.4 0.0 1.1 1.1 1.4 1.4 1.6 ... S/N 11.7 16.9 2.3 11.0 3.6 10.4 5.9 11.7 23.2 8.1 5.5 6.3 6.4 8.7 6.2 9.5 5.0 5.9 9.3 5.1 9.4 4.7 4.8 21.7 10.2 12.4 ... Runs 2 3, D97 3 2 3 4 3 3 3 4 4 4 4 4 2 2 2 2 2, 2 2 2 2 2 2 2, 2 2 2 ... Lines H/K, Hζ, Hη, Hθ,[O ii]. . . br, H/K, Hζ, Hη, Hθ. . .[O ii], Hβ,[O iii] H/K, Hδ, Hγ, G, Hβ(ab) br G, Hβ(ab), br, Mg i[O ii],[O iii], Hβ, Hγ(em), Hδ(em). . . Hθ, Hη, Hζ, Hβ,[O ii]. . . H/K, Hζ, Hη, Hθ, Hβ. . . br, G, Hθ, Hη, NaD. . . H/K, Hη, Hθ, G H, Hγ, Hη Hγ, Hδ, G H/K, Hζ, Hη, Hθ, G. . . G, Hγ, Hδ, H/K, Hζ Hδ, G, Hγ, Hβ(ab), Hθ. . . H/K, Hδ, G, Hγ, Hθ. . . Hδ, H/K, Hθ, Hζ, G H/K, Hζ, Hη, G, Hβ(e+a). . . br,[O ii] NaD, Mg i, bands[O iii],[O ii] Mg i, Fe i, G, Hγ, br. . .[O ii], Hβ,[O iii], G, Hγ(em). . . H/K, Hζ, Hη, Hθ,[O ii]. . . H/K, Hδ, G, Hγ, Hβ(ab). . . br, H/K, Hθ, Hζ, Hη. . . ...

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

10O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.The

catalogue

Fig.4b.Continued.ThesquaresmarkthepositionsofFigs.9,thecircletheareaaroundtheweakshearsignaldetectedbyBonnet,Mellier&Fort(1994),discussedinSect.4.

Fig.4c.Continued

Column14:Signal-to-noiseratiomeasuredbetween4050and4250 A.

Column15:Number(s)oftheobservingrun(s)duringwhichtheobjectwasobserved(cf.Table1).Objectsob-servedbyDressleretal.(1999)aremarkedby“D”andthenumberfromtheircatalogue.

Column16:Linesthatcouldbeidenti edinthespec-trum/spectra.

Weprovidenewspectrafor618objects,ofwhich581haveredshifts.Theglobalsuccessrateistherefore94%.Notallredshiftsareequallysecurethough:Wequalify435ofourredshifts(70%)as“secure”(qualitycodeA),28(5%)as“uncertain”(codeD)and86(14%)ofinter-mediatequality.34objects(5%)turnedouttobestars.Thefractionof“secure”redshiftsis83%forforeground

galaxiesatz<0.37,82%forgalaxiesaroundthecluster

redshift(0.37<z<0.41),anddropsto53%forgalaxiesathigherredshift.

Forcompleteness,weincludeinthecataloguethered-shiftsprovidedbyDressleretal.(1999).Thecorrespond-ingentrynumberfromtheircatalogue(pre xedby‘D’)islistedincolumn15ofourcatalogue.ThecatalogueaspublishedbyDressleretal.(1999)contains130entries,ofwhich107areclustermembers.However,wenoticedseveralerrorsintheircatalogue,reducingthenumberofdistinctobjectsto1255.54oftheseobjectswereobservedbyusaswell,usuallywithconcordantredshifts,seethediscussioninSec.3.2andFig.3.Therewerehowever veproblematiccases:Dressleretal.givetheredshiftforob-ject376(D7)as0.3755,whereasourspectrumindicates

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

11

Fig.4d.

Continued

Fig.4e.

Continued

Fig.4f.

Continued

Fig.4g.Continued

asecure0.3955.WeassumethatthisisatypographicalerrorintheDressleretal.listandadoptourvalue.Ourspectrumforobject416(D33)indicatesz=0.3895asopposedtotheir0.4035.SinceDressleretal.onlygivethisaqualitycode‘3’,weadoptourvalue.Object289(D109)issimilarlyuncertain.Object466shouldbeiden-ticaltoDressleretal.’sobjectD37,howeverthespectraarecompletelydi erentgivingsecureredshiftsof0.3916and0.1840respectively.WehavetoassumethereforethatD37haswrongcoordinates.AsimilarproblemoccursforD130(our237).

Addingthe69objectswhichwereobservedbyDressleretal.aloneincreasesthesizeofthecatalogueto687ob-jects,with650identi edredshifts.

pleteness

Fig.5presentscolour-magnitudediagrams(CMDs)forthephotometric(fortheoverlapregionoftheCFH12kandUH8kimages)andthespectroscopiccatalogues.ForthelattercataloguewealsoshowseparateCMDsforforegroundgalaxiesatz<0.37,backgroundgalaxiesatz>0.41,galaxiesattheclusterredshift(0.37<z<0.41)andforanewlyidenti edgroupofgalaxiesatz=0.495(seeSect.4).

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

12O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.The

catalogue

Fig.4h.Continued

TheprimarycriterionforthecandidateselectionforthespectroscopicsurveywasV<23.ThecompletenessinVmagnitudeofthe nalcatalogueisshowninFig.6,whereforeachgalaxyfromthespectroscopiccataloguewecountthenumberofobjectsinabinof±0.25magaroundthegalaxymagnitudeinboththespectroscopicandpho-tometriccatalogues(thelatterrestrictedtothesurveyareaasoutlinedinFig.7)andde netheirratioastheto-talcompletenessatthegivenmagnitude.BetweenV 20andV 22thecompletenessisroughlyconstantat～45%anddropsrapidlyforfaintermagnitudes.Restrictingthesameanalysistothecentralareawithin3′oftheclustercentre(usinglargerbinsof±0.5mag)showsthatinthisregionthecompletenessexceeds80%betweenV 20andV 22.

Avisualimpressionofthevariationofthecomplete-nessacrossthesurveyareaisgiveninFig.7whereweuseanadaptivetop-hat(itsradiusatanygivenpointofagridisthegeometricmeanofthedistancestothe10thand11thnearestobjectswithspectroscopy)tocomputetheratioofthenumbersofobjectswithspectroscopy( xedto10)andthenumberofobjectsinthephotometriccata-logue.Inordertohavesampleswithwell-de ned(thoughaposteriori)photometricselectionlimitswerestrictthespectroscopicandphotometriccataloguesforthispurposetosubsampleswith20<V<23and0.6<V I<2.4.AsFig.5shows,thisregionofthecolour-magnitudeplaneenclosesvirtuallyalltheclustermembersinthespectro-scopiccatalogue.Withinourrestrictedsamplethesepa-rationbetweenstarsandgalaxieswithinthephotomet-riccatalogueisfairlystraightforwardusingSExtractor’sCLASS

zN=0.4921and

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

13

Fig.5.V-Icolour-magnitudediagrams.Thetop-leftdia-gramshowsthefullphotometriccatalogue,thetop-rightdiagramthefullspectroscopiccatalogue.Thenextthreediagramssplitthespectroscopiccatalogueaccordingtoredshift,showingforegroundandbackgroundgalaxiesaswellasgalaxiesaroundtheclusterredshiftz～0.39.NotetheclearlyvisibleclustersequenceatV I 2inthelatterdiagram.Thebottom-rightdiagramshowsthemembersofthe

newlydiscoveredgroupofgalaxiesatz～0.495(seeSection4).Theparallelogrammarksthesubsampleusedinthecompletenessmap(Fig.7),20<V<23,0.6<V I<2.4.

pletenessofthespectroscopicsurveyinVmagnitude.Foreachgalaxyfromthecataloguethisisgivenastheratioofthenumbersofgalaxiesinthespec-troscopicandphotometriccataloguesinagivenbinwidthcenteredonthemagnitudeofthegalaxy.Plusesmarkgalaxiestakenfromthewholesurveyarea(asoutlinedinFig.7),crossesgalaxieswithin3′oftheclustercentre.Intheformercase,abinwidthof0.5magwasused,inthelatterabinwidthof1mag.

Fig.7.Mapofthecompletenessvariationofthespectro-scopiccatalogueasgray-scalewithoverlaidcontours.Thecompletenessatanypointisdeterminedinacirculartop-hatencompassingthe10nearestneighboursinthespec-troscopicsurvey;themapissmoothedwithaGaussianofwidth30′′.Contourlinesarespacedin10%steps.The50%contourismarkedbyaboldline,contoursatlessthan50%aredrawninblack,highercontoursinwhite.

persionsarepresumablyenhancedbytidalinteractionbe-tweenthegroups.

Fig.9showscolourimagesofthenorthernandsouth-erngroupscreatedfromtheI-andV-bandCCDimages.Thegalaxyatz=0.4907issurroundedbythreeobjectsofsimilar,bluecolour.Itistemptingtointerpretthisgroupasmultipleimagesofthesamebackgroundob-ject.Inthiscase,usingthecurvatureradius(～5′′)asanestimatefortheEinsteinradiusandzs=1asaroughguessfortheredshiftofthebackgroundsource,weobtain5.8×1012h 1M⊙forthemasswithinthisradius.

AnotheroverdensityinFig.8occursatz～0.18.Thesegalaxiesarehoweverdistributedfairlyuniformlyacrossthe eldwithnoobviousspatialconcentrationandarethereforejustpartofthegenerallarge-scalestructureintheUniverse.

Inthe rstdetectionofacoherentshear eldaroundaclusterofgalaxies,Bonnetetal.(1994)foundasignaltothenorth-eastofthecentreofCl0024+1654,indicatingaconcentrationofmassatapointwherenooverdensityofgalaxiesisapparentinthetwo-dimensionalimages.Thedirectiontothisdark“clump”isindicatedbyacirclein

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

14O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.The

catalogue

Fig.8.Three-dimensionaldistributionoftheobjectsinourredshiftcatalogue.Inthetwoupperpanelstheobjectsareprojectedontotherightascensionaxis,inthelowertwoontothedeclinationaxis.Theupperpanelofeachpairshowsthelarge-scaledistributionfromz=0toz=1,thelowerpanelanexpandedviewoftheenvironmentoftheclusterCl0024itself.ThedashedlinemarksthedirectiontowardsthepotentialperturbationdetectedbyBonnetetal.(1994).Twogroupsatz～0.495aremarkedbyrectangles.TheconversionfromangularpositionontheskytopropertransversedistancewasdoneassuminganEinstein-deSitterUniversewithH0=100kms 1Mpc 1.Fig.4bandbythedashedlineinFig.8.Thereisnosig-ni cantover-densityalongthislinewhichcouldexplainthespatialtightnessofthesignalobservedbyBonnetetal.

5.Conclusions

Inthispaperwepresentacatalogueofspectroscopicdatafor687objectsina eldof21×25arcmin2aroundthecen-treoftheclusterofgalaxiesCl0024+1654atz～0.395,295ofwhichlieinthevicinityoftheclusteritself,intherange0.37<z<0.41.Thecompletenessofthesampleexceeds80%aroundtheclustercentreforV<22,droppingto～70%forV<!23.Themeancompletenessoverthewhole

Fig.9.“True”colourimagesoftheapparentcentresofthenorthern(top)andsouthern(bottom)groupsofgalaxiesatz 0.49.TheimageswerecreatedfromtheVandIbandimages,thegreenchannelisanaverageofthesetwoimages.Supposedmembergalaxiesofthegroupareconspicuousbytheiryellowcolour,correspondingtoV I～2.4.Notethebluearc-likestructurearoundthegalaxyatz=0.4907.

eldisabout45%downtoV=22.Thisisthereforeoneofthelargestspectroscopicsurveysavailableforaclusteratz>～0.2andthelargestatz～0.4.Apartfromredshiftsthecataloguelistsphotometricdataandequivalent widthsfor velinesaswellasthestrengthofthe4000Abreak,importantfordeterminingpresentandrecentstarform-ingactivity.Thecataloguerepresentsauniquedatabaseforinvestigationsintothestructureofamedium-redshiftclusterofgalaxiesanditsenvironment.

Wereportthediscoveryofabinarygroupofgalaxiesatz 0.495,whichincludesagravitationalarccandidate.Afurtheroverdensityintheredshiftdistributionatz～0.18canatpresentnotbeattributedtoacollapsedstructure,althoughwecannotexcludethepossibilitythatacentreforsuchastructureexistsoutsidethe eldcoveredbyoursurvey.Noneofthestructuresseenintheredshiftdistributionseemstobeabletoexplainthecoherentshearsignalat～6′tothenorth-eastoftheprojectedcentreofCl0024+1654,detectedbyBonnetetal.(1994).

ThemainresultofthisprojectisthatCl0024+1654isnotasimpleisolatedcluster,ashashithertobeenassumedininterpretingkinematical,lensingandX-raydata.Insteadthereisasecond,lessmassiveclusterpro-jectedontothecentreofthemaincluster.TheseparationofCl0024+1654intotwocomponentshasstrongconse-quencesfortheinterpretationofobservationaldataandshouldinparticularhelptoresolvethewell-knowndis-crepancybetweenmassesdeterminedusingdi erentmeth-odsforthiscluster(Soucailetal.2000).ThestructureofCl0024+1654,ascenarioforpossibleinteractionbetweenthemainandforegroundclustersandthee ectsofthisinteractiononthepropertiesoftheclustergalaxypopula-tionswillbediscussedinmoredetailinthesecondpaperofthisseries(Czoskeetal.2001).ThephotometricdataobtainedinconjunctionwiththisprojectwillbeusedbyMayenetal.(2001)toinvestigatethedepletionofback-groundobjectsduetothegravitationallensinge ectofCl0024+1654.

Acknowledgements.OCthankstheEuropeanCommissionforgeneroussupportundergrantnumberER-BFM-BI-CT97-2471.JPKthanksCNRSforsupportandacknowledgesaEuropeanLargeScaleFacilitygrantfortheWHTobservation.ThisworkwassupportedbytheTMRNetwork“GravitationalLensing:NewConstraintsonCosmologyandtheDistributionofDarkMatter”6oftheEuropeanCommissionundercon-

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

O.Czoskeetal.:SpectroscopicsurveyofCl0024:I.Thecatalogue

15

tractNo.ER-BFM-RX-CT97-0172.TJBwishestothankObservatoireMidi-Pyr´en´eesforhospitality.

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We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

This figure "figure9_N.jpg" is available in "jpg" format from:

/ps/astro-ph/0103123v1

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final

This figure "figure9_S.jpg" is available in "jpg" format from:

/ps/astro-ph/0103123v1

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