An Australia Telescope survey for CMB anisotropies

Abstract

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