The Australia Telescope search for cosmic microwave background anisotropy

In an attempt to detect cosmic microwave background (CMB) anisotropy on arcmin scales, we have made an 8.7-GHz image of a sky region with a resolution of 2 arcmin and high surface brightness sensitivity using the Australia Telescope Compact Array (ATCA) in an ultracompact configuration. The foreground discrete-source confusion was estimated from observations with higher resolution at the same frequency and in a scaled array at a lower frequency. Following the subtraction of the foreground confusion, the field shows no features in excess of the instrument noise. This limits the CMB anisotropy flat-band power to Q(flat) < 23.6 mu K with 95 per cent confidence; the ATCA filter function (which is available at the website www.atnf.csiro.au/Research/cmbr/cmbr atca.html) F-l in multipole l-space peaks at l(eff) = 4700 and has half-maximum values at l = 3350 and 6050.