Cosmic microwave background observations with the Jodrell Bank-IAC interferometer at 33 GHz

Abstract

This paper presents the first results obtained with the Jodrell Bank–IAC two-element 33-GHz interferometer. The instrument was designed to measure the level of the cosmic microwave background (CMB) fluctuations at angular scales of 1°–2°. The observations analysed here were taken in a strip of the sky at Dec.=+41° with an element separation of 16.7λ, which gives a maximum sensitivity to ∼16 structures on the sky. The data processing and calibration of the instrument are described. The sensitivity achieved in each of the two channels is 7 μK per resolution element. A reconstruction of the sky at Dec.=+41° using a maximum entropy method shows the presence of structure at a high level of significance. A likelihood analysis, assuming a flat CMB spatial power spectrum, gives a best estimate of the level of CMB fluctuations of for the range l=109±19; the main uncertainty in this result arises from sample variance. We consider that the contamination from the Galaxy is small. These results represent a new determination of the CMB power spectrum on angular scales at which previous results show a large scatter; our new results are in agreement with the theoretical predictions of the standard inflationary cold dark matter models.