A preliminary detection of arcminute-scale cosmic microwave background anisotropy with the BIMA array

We have used the Berkeley-Illinois-Maryland Association (BIMA) array outfitted with low-noise millimeterwave receivers to expand our search for arcminute-scale anisotropy of the cosmic microwave background (CMB). The interferometer was placed in a compact configuration for sensitivity on arcminute scales over its 6.'6 FWHM held of view. This experiment is most sensitive to hat band power described by an average multipole of l = 5530, corresponding to an angular scale of similar to2'. We present the analysis of 11 independent fields that were selected based on their low contrast in infrared dust emission and lack of bright radio sources. Applying a Bayesian analysis to the visibility data, we find CMB anisotropy flat band power Q(flat) = 6.1(-4.8)(+2.8), muK at 68% confidence. The measured signal exceeds that expected from instrument noise with 76% confidence, and we find an upper limit of Q(flat) < 12.4 <mu>K at 95% confidence. We have supplemented our BIMA observations with concurrent observations at 4.8 GHz with the Very Large Array to search for and remove point sources. We find that point sources make an insignificant contribution to the observed anisotropy.