LIMITS ON THE ANISOTROPY OF THE MICROWAVE BACKGROUND-RADIATION ON ARCMINUTE SCALES .2. THE RING EXPERIMENT

Observations at a frequency of 20 GHz with the Owens Valley Radio Observatory 40 m telescope are used to place limits on the anisotropy of the cosmic microwave background radiation on arcminute angular scales. The new experiment, designated the RING, consists of a survey of 96 fields at declination delta = 88-degrees 10-'42'', observed in an interlocked ringlike geometry that provides improved discrimination against systematic biases and allows reconstruction of the intrinsic fluctuations from the differenced data. The RING experiment has high sensitivity for a variety of non-Gaussian fluctuation models but is susceptible to contamination by discrete extragalactic radio sources. Where possible, lower frequency VLA observations were used to identify and correct for the contributions of these objects. Statistical analysis of the RING data results in detections of anisotropy of 2.3 < DELTAT/T < 4.5 x 10(-5) (95%) and 1.6 < DELTAT/T < 6.1 x 10(-5) (99.87%), assuming T(mwb) = 2.735 K, for Gaussian fluctuations that are uncorrelated between the RING fields. The amplitude of these fluctuations is significantly higher than that predicted for CDM models consistent with the recent COBE results and is also inconsistent at the 95% confidence level with earlier measurements using the same instrument. Because of the high likelihood of residual radio source contamination, these detections are treated as upper limits on intrinsic background fluctuations. Of the 96 RING fields, seven fields were found to have signals of 3 sigma or greater, and four of these were subsequently shown to be contaminated with extragalactic nonthermal radio sources. One of the remaining fields, which exhibits a 5 sigma fluctuation, has not been identified with any known foreground source and is the best candidate field for a background fluctuation, although foreground contamination has not been ruled out. In conjunction with previous observations, we find AT/T < 10(-4) for Gaussian fluctuations with correlation angles between 0.'7 and 7' (95%). Implications for cosmology and theories of galaxy formation are discussed.