The SCUBA HAlf Degree Extragalactic Survey (SHADES) - III. I(3)

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

Identi cationofsubmillimetregalaxiesintheSHADESSourceCatalogue

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Figure1.IndividualpointingsforradiomosaicsintheSHADES elds,togetherwithanindicationofthesubmmcoverage.ThediameterofthecirclesistheFWHMoftheVLA’sprimarybeamat1.4GHz.

2OBSERVATIONS2.11.4-GHzradioimaging

Wide- eldradioimageswereobtainedusingtheVLA.TheLHdatausedhere,comprising75hrofintegrationona elddesignatedLOCKMAN-E,weredescribedindetailbyIvisonetal.(2002).Thedatahavesincebeenre-analysedbyBiggs&Ivison(2006),usingthe37-piecemosaicingtechniquedescribedbyOwenetal.(2005),togetherwithadditionalself-calibration.Theresultingimagecov-ersmostoftheprimarybeam,outtoaradiusof23arcmin.Oncecombined,thenoiselevelisunusuallyuniform,4.2µJybeam 1r.m.s.inthecentreofthe eld,witha1.3-arcsecsynthesisedbeam(FWHM).

Wealsoutiliseanewlow-resolutionmap,madebytaperingourLOCKMAN-Edatatogivea4.2-arcsecsynthesisedbeamandthenmosaicingwithB-con gurationdatatakenforseveralnearbypointings:anew eld,11arcmintothesouthwest,designatedLOCK-3,plusarchivaldatafor eldsdesignatedLHEX1,LHEX2,LHEX3andLHEX4,whereLHEX4comprises31hrofintegration,11arcmintothenortheastofLOCKMAN-E.Fig.1illustratesthemosaicofpointings.Thesedata,togetherwithmatched-resolution610-MHzimagingfromtheGiantMetre-waveTelescopeinPune,India,aredescribedbyIbaretal.(inpreparation).

Weobtainednew1.4-GHzdatafortheSXDF,againusingtheVLA,during2003.Manyofthesedatawereaffectedbyinterfer-

c0000RAS,MNRAS000,000–000enceandbyaprolongedfailureofthecorrelator,buttheequiva-lentofaround60hrofnormalintegrationweresalvaged.TheseA-con gurationdatawerecombinedwiththeB-andC-con gurationdatadescribedbySimpsonetal.(2006)resultingina9:3:1ratioofrecordedA:B:Cvisibilities,evenlydistributedinthreepoint-ingsseparatedby15arcmin(seeFig.1).Eachpointingwasimagedasa37-piecemosaic,aswiththeLH.The nalimagewasknit-tedtogetherandcorrectedfortheresponseoftheprimarybeamusingtheAIPStask,FLATN.Theresultingnoiselevelisaround6.3µJybeam 1inthebestregionsofthemap,thoughashighas8.4µJybeam 1nearbright,complexradioemitters,withasynthe-sisedbeammeasuringaround1.7arcsec(FWHM).AswiththeLH,wealsoutilisealow-resolutionmap,taperingourentiredatasettogivea4.2-arcsecsynthesisedbeam.

2.2Opticalimaging

R-bandopticalimagingfortheLHandSXDFwereobtainedusingtheSubaru8-mtelescope.TheLHdataweretakenfromthearchiveandaredescribedinIvisonetal.(2004)andreacha3σdepthof27.7mag;similardataforSXDFaredescribedbyFurusawaetal.(inpreparation),reachinga3σdepthof27.5mag(bothontheVegascale,for2-arcsec-diameterapertures).

2.3Near-andmid-IRimaging

Thenear-andmid-IRdataemployedherewereobtainedusingIRAC(at4.5and8µm)andMIPS(at24µm).Theimagingcov-erstheentireSHADESregionoftheLHtonear-uniformdepthsofσ=0.54,4.4and11µJyat4.5,8and24µm,respectively(Egamietal.,inpreparation),with uxcalibrationaccurateto±10percent,thatisapproximately3×deeperat24µmthanthedatausedbyEgamietal.(2004),Serjeantetal.(2004)andIvisonetal.(2004).IntheSXDF,IRACandMIPSdataareavailablefromtheSpitzerWide-areaInfraRedExtragalactic(SWIRE–Lonsdaleetal.2003)surveyandreachanear-uniformdepthofσ=1.1,7.5and48µJyat4.5,8and24µm(Shupeetal.,inpreparation).Forcomparison,the5-σconfusionlimitat24µm,with20beamspersource,isaround56µJy.

3ASSOCIATIONSBETWEENSUBMMGALAXIESAND

RADIO/MID-IRSOURCESObservationsinthesubmmwavebandaresensitivetocolddustcreatedforthemostpartbysupernovae(SNe)andstellarwinds,re-radiatingenergyabsorbedfromhot,youngstars(Whittet1992).TheradiowavebandisalsosensitivetoSNe–andhencetorecentstarformation–viasynchrotronradiationfromrelativisticelec-trons.Near-IRwavelengthsprobephotosphericemissionfromstarsandinthemid-IR,at24µm,wearesensitivetoemissionfromdustinthecircumnucleartorusofAGNandtothewarmestdustinstar-bursts.ThecorrelationbetweensubmmandradioemissionfromSMGsispoorerthanexpected(fromlocalstudies–e.g.Dunneetal.2000),probablyduetoawiderangeofcharacteristicdusttemperaturesandtotheeffectofradio-loudAGN;nevertheless,predictingtherest-framefar-IRpropertiesofSMGsisbetterac-complishedfromtheradioendoftheSEDthanfromthenear-ormid-IR,addingtothebene tofveryhighspatialresolution(～0.1arcsec)availableatradiowavelengths(Chapmanetal.2004;Muxlowetal.2005;Biggsetal.,inpreparation)andmakingitthe