2006ApJ...647...13D

We report the final results of our study of the cosmic microwave background (CMB) with the BIMA array. Over 1000 hr of observation were dedicated to this project exploring CMB anisotropy, on scales between 1' and 2' in eighteen 6'.6 FWHM fields. In the analysis of the CMB power spectrum, the visibility data are divided into two bins, corresponding to different angular scales. Modeling the observed excess power as a flat band of average multipole l_eff=5237, we find ΔT²₁=220⁺¹⁴⁰_–120µK² at 68% confidence and ΔT²₁>0 µK² with 94.7% confidence. In a second band, with average multipole of l_eff=8748, we find ΔT²₂ consistent with zero and an upper limit of 880 µK² at 95% confidence. An extensive series of tests and supplemental observations with the VLA provide strong evidence against systematic errors or radio point sources being the source of the observed excess power. The dominant source of anisotropy on these scales is expected to be the Sunyaev-Zel'dovich (SZ) effect in a population of distant galaxy clusters. If the excess power is due to the SZ effect, we can place constraints on the normalization of the matter power spectrum σ₈=1.03^+0.20_–0.29 at 68% confidence. The distribution of pixel fluxes in the BIMA images is found to be consistent with simulated observations of the expected SZ background and rules out instrumental noise or radio sources as the source of the observed excess power, with confidence similar to the detection of excess power. Follow-up optical observations to search for galaxy overdensities anticorrelated with flux in the BIMA images, as might be expected from the SZ effect, proved to be inconclusive.