The radio source counts at 15 GHz and their implications for cm-wave CMB imaging

A B ST R A C T W e presentthe prelim inary results ofa new survey ofradio sourcesusing the Ryle Telescopeat15.2 GHz.Thisisthehighestfrequency atwhich a survey hasbeen done thatisrelevantto theissueofradio sourcecontam ination in CM B experim ents.The dierentialsourcecountofthe 66 sourcesfound in 63 deg 2 is80(S=Jy) 2:0 Jy 1 sr 1 , from � 20 m Jy to � 500 m Jy.Extrapolating thisto 34 GHz (where m any cm -wave CM B experim ents operate) gives an estim ated tem perature contribution ofsources �T conf = 9�K in a CM B im age,with a beam corresponding to m ultipole l � 500.A m eansofsourcesubtraction isevidently necessary,otherwisethesignal-to-noiseratio in CM B im ages willbe lim ited to 4 or 5,becom ing worse at higher resolution.W e com pare the population ofsourcesobserved in thisnew survey to thatpredicted by extrapolation from lowerfrequency surveys,�nding thatsourceuxes,and indeed the existenceofm any sources,cannotbedeterm ined by extrapolation. K ey w ords: cosm icm icrowavebackground { surveys{ radio continuum :galaxies