Detection of cosmic microwave background structure in a second field with the Cosmic Anisotropy Telescope

J. C. Baker, K. Grainge, M. Hobson, M. E. Jones, R. Kneissl, A. Lasenby, C. M. M. O'Sullivan, G. G. Pooley, G. Rocha, R. D. Saunders, P. Scott, E. Waldram

Abstract
We describe observations at frequencies near 15GHz of the second 2x2deg² field imaged with the Cambridge Cosmic Anisotropy Telescope (CAT). After the removal of discrete radio sources, structure is detected in the images on characteristic scales of about half a degree, corresponding to spherical harmonic multipoles in the range l~330-680. A Bayesian analysis confirms that the signal arises predominantly from the cosmic microwave background (CMB) radiation for multipoles in the lower half of this range; the average broad-band power in a bin with centroid l=422 (θ~51arcmin) is estimated to be ΔTT 2.1_-0.5^+0.4 x10^-5. For multipoles centred on l=615 (θ~35arcmin), we find contamination from Galactic emission is significant, and constrain the CMB contribution to the measured power in this bin to be ΔTT < 2.0x10^-5 (1σ upper limit). These new results are consistent with the first detection made by CAT in a completely different area of sky. Together with data from other experiments, this new CAT detection adds weight to earlier evidence from CAT for a downturn in the CMB power spectrum on scales smaller than 1deg. Improved limits on the values of H₀ and Ω are determined using the new CAT data.

Monthly Notices of the Royal Astronomical Society
Volume 308, Page 1173
October 1999