An Upper Limit to Arcminute‐Scale Anisotropy in the Cosmic Microwave Background Radiation at 142 GHz

We present limits to anisotropies in the cosmic microwave backgroundradiation (CMB) at angular scales of a few arcminutes. The observations weremade at a frequency of 142 GHz using a 6-element bolometer array (theSunyaev-Zel'dovich Infrared Experiment) at the Caltech SubmillimeterObservatory. Two patches of sky, each approximately 36'x4' and free of knownsources, were observed for a total of 6-8 hours each, resulting inapproximately 80 independent 1.7' full-width half-maximum pixels. Each pixel isobserved with both a dual-beam and a triple-beam chop, with a sensitivity perpixel of 90-150 uK in each chop. These data have been analyzed using maximumlikelihood techniques by assuming a gaussian autocorrelation function for thedistribution of CMB fluctuations on the sky. We set an upper limit of Delta T/T<= 2.1 x 10^{-5} (95% confidence) for a coherence angle to the fluctuations of1.1. These limits are comparable to the best limits obtained fromcentimeter-wavelength observations on similar angular scales but have theadvantage that the contribution from known point sources is negligible at thesefrequencies. They are the most sensitive millimeter-wavelength limits forcoherence angles <= 3'. The results are also considered in the context ofsecondary sources of anisotropy, specifically the Sunyaev-Zel'dovich effectfrom galaxy clusters.Comment: ApJ accepted, 37 pages Latex (AASTEX), 13 encapsulated postscript figure