The Star-formation History of the Universe as Revealed from Deep Radio Observations of the

Discerning the exact nature of the faint (sub-mJy) radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep observations from Chandra/XMM-Newton/Spitzer and ground based follow up we are ab

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a**FULLTITLE**ASPConferenceSeries,Vol.**VOLUME**,**YEAROFPUBLICATION****NAMESOFEDITORS**TheStar-formationHistoryoftheUniverseasRevealedfromDeepRadioObservationsofthe13HXMM-Newton/ChandraDeepFieldN.Seymour1,T.Dwelly2,D.Moss2,I.McHardy2,M.Page3,N.Loaring4,3andG.Reieke5Abstract.Discerningtheexactnatureofthefaint(sub-mJy)radiopopula-tionhasbeenhistoricallydi cultduetothelowluminosityofthesesourcesatmostwavelengths.UsingdeepobservationsfromChandra/XMM-Newton/SpitzerandgroundbasedfollowupweareabletodisentangletheAGNandstar-formingpopulationsforthe rsttimeinadeepmulti-frequencyGMRT/VLA/MERLINSurvey.Themanydiagnosticsincluderadioluminosity,morphology,radiotomid-IR uxdensityratios,radiotooptical uxdensityratiosandradiospec-tralindices.Furtherdiagnostics,e.g.opticalspectraX-rayspectra/hardnessratios,IRcoloursindicatethepresenceoftheAGNindependentofwhethertheradioemissionispoweredbyAGNorstar-formation.Weareabletoexaminethestar-formationhistoryoftheuniverseuptoz=2.5inauniquewaybasedonanunbiasedstar-formationrateindicator,radioluminosity.Thisworkpro-videsanalternativeperspectiveonthedistributionofstar-formationbymass,“downsizing”andallowsustoexaminetheprevalenceofAGNinstar-bursts.1.IntroductionAbovea uxdensityof1mJythesourceswhichdominatethe1.4GHzradiosourcecountsarealmostexclusivelyAGN.Howeverbelow1mJythereisanexcessovertheextrapolationfromhigher uxeswhichisknownasthe“sub-mJybump”(Richards2000;Hopkinsetal.2003;Seymouretal.2004).Theconventionalviewisthatthebumparisesfromstar-burstemission(Condon1992;Richards2000).Attemptstodeterminetheseparateevolutionofthe

star-burstandAGNpopulationshavebeenseverelyhamperedbythescarcityofgenuinemulti-wavelengthdatasetsondeepradiosurveys.Sourceevolu-tionisconstrained,ratherpoorly,onlybytheshapeofthesourcecounts(e.g.Hopkinsetal.2003;Seymouretal.2004,Mossetal.inprep.)

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