Two years of microwave background observations with the Cosmic Background Imager (CBI) have been combined to give a sensitive, high resolution angular power spectrum over the range 400 < ℓ < 3500. This power spectrum has been referenced to a more accurate overall calibration derived from the Wilkinson Microwave Anisotropy Probe. The data cover 90 deg 2 including three pointings targeted for deep observations. The uncertainty on the ℓ > 2000 power previously seen with the CBI is reduced. Under the assumption that any signal in excess of the primary anisotropy is due to a secondary Sunyaev-Zeldovich anisotropy in distant galaxy clusters we use CBI, Arcminute Cosmology Bolometer Array Receiver, and Berkeley-Illinois-Maryland Association array data to place a constraint on the present-day rms mass fluctuation on 8 h −1 Mpc scales, σ 8 . We present the results of a cosmological parameter analysis on the ℓ < 2000 primary anisotropy data which show significant improvements in the parameters as compared to WMAP alone, and we explore the role of the small-scale cosmic microwave background data in breaking parameter degeneracies.

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We present results from microwave background observations at the Owens Valley Radio Observatory. These observations, at 14.5 and 32 GHz, are designed to detect intrinsic anisotropy on scales of 7'. After point source removal, we detect significant emission with temperature spectral index beta ~ -2 towards the North Celestial Pole (NCP). Comparison of our data with the IRAS 100 micron map of the same fields reveals a strong correlation between this emission and the infrared dust emission. From the lack of detectable H-alpha emission, we conclude that the signals are consistent either with flat-spectrum synchrotron radiation, or with free-free emission from T_e ~ 10^6 K gas, probably associated with a large HI feature known as the NCP Loop. Assuming beta = -2.2, our data indicate a conversion T_f/I_(100 micron) = 0.075*nu(GHz)^-2.2 K/(MJy/sr). The detection of such a component suggests that we should be cautious in any assumptions made regarding foregrounds when designing experiments to map the microwave background radiation.Comment: 6 pages, Latex, 3 Postscript figures, uses aas2pp4.st

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