An Australia Telescope survey for CMB anisotropies

We have surveyed six distinct 'empty fields' using the Australia Telescope Compact Array (ATCA) in an ultracompact configuration with the aim of imagi ng, with a high brightness sensitivity, any arcminute-scale brightness-temp erature anisotropies in the background radio sky. The six well-separated re gions were observed at a frequency of 8.7 GHz, and the survey regions were limited by the ATCA primary beams which have a full width at half-maximum o f 6 arcmin at this frequency; all fields were observed with a resolution of 2 arcmin and an rms thermal noise of 24 mu Jy beam(-1). After subtracting foreground confusion detected in higher resolution images of the fields, re sidual fluctuations in Stokes I images are consistent with the expectations from thermal noise and weaker (unidentified) foreground sources; the Stoke s Q and U images are consistent with expectations from thermal noise. Within the sensitivity of our observations, we have no reason to believe th at there are any Sunyaev-Zeldovich holes in the microwave sky surveyed. Ass uming Gaussian-form CMB anisotropy with a 'flat' spectrum, we derive 95 per cent confidence upper limits of Q(flat) < 10-11 mu K in polarized intensit y and Q(flat) < 25 mu K in total intensity. The ATCA filter function peaks at l = 4700 and has half-maximum values at l = 3350 and 6050.