Determining an accurate position for a submm galaxy (SMG) is the crucial step that enables us to move from the basic properties of an SMG sample - source counts and 2-D clustering - to an assessment of their detailed, multi-wavelength properties, their con

Mon.Not.R.Astron.Soc.000,000–000(0000)Printed5February2008

A(MNLTEXstyle lev2.2)

TheSCUBAHAlfDegreeExtragalacticSurvey—III.Identi cation

ofradioandmid-infraredcounterpartstosubmillimetregalaxies

R.J.Ivison,1,2T.R.Greve,3J.S.Dunlop,2J.A.Peacock,2E.Egami,4IanSmail,5E.Ibar,2E.vanKampen,6I.Aretxaga,7T.Babbedge,8A.D.Biggs,1A.W.Blain,3S.C.Chapman,9D.L.Clements,8K.Coppin,5,10D.Farrah,11M.Halpern,10D.H.Hughes,7M.J.Jarvis,12T.Jenness,13J.R.Jones,14A.M.J.Mortier,2S.Oliver,15C.Papovich,4P.G.P´erez-Gonz´alez,16A.Pope,10S.Rawlings,17G.H.Rieke,4M.Rowan-Robinson,8R.S.Savage,15D.Scott,10M.Seigar,18S.Serjeant,19C.Simpson,20J.A.Stevens,12M.Vaccari,21,8J.Wagg7,22andC.J.Willott23

UKAstronomyTechnologyCentre,RoyalObservatory,BlackfordHill,EdinburghEH93HJ

ScottishUniversitiesPhysicsAlliance,InstituteforAstronomy,UniversityofEdinburgh,BlackfordHill,EdinburghEH93HJ3AstronomyDepartment,CaliforniaInstituteofTechnology,Pasadena,CA91125,USA

4StewardObservatory,UniversityofArizona,933N.CherryAvenue,Tuscon,AZ85721,USA5InstituteforComputationalCosmology,UniversityofDurham,SouthRoad,DurhamDH13LE6InstituteforAstrophysics,UniversityofInnsbruck,Technikerstr.25,A-6020Innsbruck,Austria7InstitutoNacionaldeAstrof´ sica,OpticayElectr´onica,ApartadoPostal51y216,72000Puebla,Pue.,Mexico8AstrophysicsGroup,BlackettLaboratory,ImperialCollegeLondon,PrinceConsortRoad,LondonSW72BW9InstituteofAstronomy,MadingleyRoad,Cambridge,CB30HA

10DepartmentofPhysics&Astronomy,UniversityofBritishColumbia,Vancouver,BCV6T1Z1,Canada11DepartmentofAstronomy,CornellUniversity,106SpaceSciences,Ithaca,NY14853,USA

12CentreforAstrophysicsResearch,UniversityofHertfordshire,CollegeLane,Hat eldAL109AB13JointAstronomyCentre,660N.A‘oh¯ok¯uPlace,UniversityPark,Hilo,HI96720,USA14CenterforAstrophysicsandSpaceAstronomy,389UCB,Boulder,CO80309,USA15AstronomyCentre,UniversityofSussex,Falmer,BrightonBN19QH16DepartmentodeAstrof´ sicayCC.deAtm´osfera,FacultaddeCC.F´ sicas,UniversidadComplutensedeMadrid,28040Madrid,Spain17Astrophysics,DepartmentofPhysics,DenysWilkinsonBuilding,KebleRoad,OxfordOX13RH

18DepartmentofPhysicsandAstronomy,4129FrederickReinesHall,UniversityofCalifornia,Irvine,CA92697,USA19AstrophysicsGroup,DepartmentofPhysics,TheOpenUniversity,MiltonKeynesMK76AA

20AstrophysicsResearchInstitute,LiverpoolJohnMooresUniversity,TwelveQuaysHouse,EgertonWharf,BirkenheadCH411LD21DepartmentofAstronomy,UniversityofPadova,Vicolodell’Osservatorio3,I-35122,Italy22NationalRadioAstronomyObservatory,P.O.Box0,Socorro,NM87801,USA

23PhysicsDepartment,UniversityofOttawa,150LouisPasteur,PavillonMacDonaldHall,Ottawa,OntarioK1N6N5,Canada

21

arXiv:astro-ph/0702544v2 30 May 2007

Accepted...;Received...;inoriginalform2007February20

ABSTRACT

c0000RAS

Determininganaccuratepositionforasubmillimetre(submm)galaxy(SMG)isthecrucial

stepthatenablesustomovefromthebasicpropertiesofanSMGsample–sourcecountsand2-Dclustering–toanassessmentoftheirdetailed,multi-wavelengthproperties,theircontributiontothehistoryofcosmicstarformationandtheirlinkswithpresent-daygalaxypopulations.Inthispaper,weidentifyrobustradioand/orinfrared(IR)counterparts,andhenceaccuratepositions,forovertwothirdsoftheSCUBAHAlf-DegreeExtragalacticSurvey(SHADES)SourceCatalogue,presentingoptical,24-µmandradioimagesofeachSMG.Observedtrendsinidenti cationratehavegivennostrongrationaleforpruningthesample.Uncertaintiesinsubmmpositionarefoundtobeconsistentwiththeoreticalexpectations,withnoevidenceforsigni cantadditionalsourcesoferror.Employingthesubmm/radioredshiftindicator,viaaparameterisationappropriateforradio-identi edSMGswithspectroscopicredshifts,yieldsamedianredshiftof2.8fortheradio-identi edsubsetofSHADES,somewhathigherthanthemedianspectroscopicredshift.Wepresentadiagnosticcolour-colourplot,exploitingSpitzerphotometry,inwhichweidentifyregionscommensuratewithSMGsatveryhighredshift.Finally,we ndthatsigni cantlymoreSMGshavemultiplerobustcounterpartsthanwouldbeexpectedbychance,indicativeofphysicalassociations.ThesemultiplesystemsaremostcommonamongstthebrightestSMGsandaretypicallyseparatedby2–6arcsec,～15–50/sinikpcatz～2,consistentwithearlyburstsseeninmergersimulations.

Keywords:galaxies:starburst–galaxies:formation–cosmology:observations–cosmol-ogy:earlyUniverse