Fluctuations in the microwave background at intermediate angular scales

An important distortion of the dipole pattern in the microwave background has been detected by two groups, Fabbri et al (1980), and Boughn et al (1980). Peebles (1980) has suggested that this irregularity may arise from large-scale gradients in gravitational potential due to the irregular distribution of mass in clusters of galaxies. His theory anticipates anisotropies in the microwave background at smaller angular scales. The experimental evidence for microwave background fluctuations at an angular scale of 6 deg, with an amplitude of 0.00011, plus or minus 0.00002 K is presented. Since the result has been obtained after subtraction for the galactic emission, its validity depends on the accuracy in extrapolating the gas-to-dust ratio to very small values of the neutral hydrogen column density. A larger dispersion in this ratio at high galactic latitudes would increase the dust contribution. In such a case, an upper limit of 0.00004 K is obtained for the cosmic background anisotropies at 6 deg, at 2 standard deviations.