10 to 60 Arcmin Fluctuations in the Cosmic Microwave Background

Extract

Considerable astronomical interest attaches to sensitive measurements of temperature fluctuations of the microwave background on scales of a few arcmins to a few degrees. We describe here the first in a series of experiments being carried out at Jodrell Bank which are aimed at providing reliable and repeatable information on these angular scales. The first experiment used the MK II 25m dish at λ6 cm and covered scales from 10 arcmin (the beamwidth) to 60 arcmin (twice the beamthrow). At this relatively long wavelength, the atmosphere has negligible effect on the observations and day to day repeatability consistent with receiver noise alone was obtained. The observations were made in wagging mode near the North Celestial Pole (NCP) so that the two beams alternately traced out a reference circle on the sky, radius 30 arcmin, over the course of 24 hours. The NCP field was chosen since a high sensitivity discrete source survey (Pauliny-Toth et al. 1978) was already available covering the area. This meant that antenna temperatures around the reference circle could be corrected for any source induced effects ≳0.4 mK. In addition control observations were made at positions 30 arcmin East and West of the central field, so that systematic effects due to interaction of telescope sidelobes with objects in the immediate telescope environment, could be monitored and removed.