A measurement of anisotropy in the cosmic microwave background on 7′-22′ scales

We report a measurement of anisotropy in the cosmic microwave background radiation (CMBR) on 7'-22' scales. Observations of 36 fields near the North Celestial Pole (NCP) were made at 31.7 and 14.5 GHz, using the 5.5 m and 40 m telescopes at the Owens Valley Radio Observatory (OVRO) from 1993 to 1996. Multiepoch VLA observations at 8.5 and 15 GHz allow removal of discrete source contamination. After point-source subtraction, we detected significant structure, which we identify with emission from a combination of a steep-spectrum foreground and the CMBR. The foreground component is found to correlate with IRAS 100 mu m dust emission. Lack of H alpha emission near the NCP suggests that this foreground is either high-temperature thermal bremsstrahlung (T-e greater than or similar to 10(6) K), hat-spectrum synchrotron, or an exotic component of dust emission. On the basis of low-frequency maps of the NCP, we can restrict the spectral index of the foreground to beta greater than or equal to -2.2. Although the foreground signal dominates at 14.5 GHz, the extracted CMBR component contributes 88% of the variance at 31.7 GHz, yielding an rms fluctuation amplitude of 82(-9.1)(+12.1) mu K, including 4.3% calibration uncertainty and 12% sample variance (68% confidence). In terms of the angular power spectrum, C-t = [\a(l)(m)\(2)], averaged over a range of multipoles l = 361-756, the detected broadband amplitude is delta T-le = [l(l + 1)C-l/(2 pi)](1/2) = 59(-6.5)(+8.6) mu K. This measurement, when combined with small angular scale upper limits obtained at the OVRO, indicates that the CMBR angular power spectrum decreases between l similar to 600 and l similar to 2000 and is consistent with hat cosmological models.