Studies of cosmic microwave background structure at Dec.=+40 deg - I. The performance of the Tenerife experiments

The direct identification of structure in the cosmic microwave background (CMB) is a major objective of observational cosmology. We present a detailed discussion of observations of such structure detected on a 5 deg scale in the CMB using beam-switching radiometers at 10, 15 and 33 GHz sited in Tenerife. This long-term experiment has reached sensitivities of a few tens of muK at each frequency and is now able to measure directly features believed to be of intrinsic CMB origin. We describe the critical elements of the system design capable of reaching these high sensitivities. An evaluation is made of the atmospheric water vapour contribution from the available multifrequency observations. The data taken in the high Galactic latitude part of the Dec.=+40 deg scan clearly show features which are seen in independent data sets at each frequency. Tests are given which demonstrate that these features are of celestial origin. An assessment of the Galactic and extragalactic contributions indicates that the 33-GHz results are essentially unaffected. These observations represent the first direct detection of individual hot and cold features in the intrinsic CMB arising from the initial singularity.