Annu. Rev. Astron. Astrophys. 1992. 30: 653-703
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3.3.6 OBSERVATIONS AT TENERIFE The group led by Davies has carried out a number of very sensitive searches for anisotropy of the microwave background radiation (Lasenby 1981, Lasenby & Davies 1983, Davies & Lasenby 1987, Davies et al 1987). The observations were carried out at Izana, Tenerife, at an altitude of 2,300 meters, at a frequency of 10.4 GHz. Their instrument consisted of a dual-horn radiometer with a tiltable plate reflector. The horns were kept stationary, observing two points at the same declination separated by 8°.2 on the sky. They Dicke switched between the two horns and, in addition, tilted the plate reflector so as to move the beams back and forth by 8°.2 in azimuth.

They made a deep survey of the circle at delta = 40° (Davies et al 1987). These observations provide impressive sensitivity in the range of angular scales > 8°. The most sensitive observations were made of the area of sky in the right ascension range 180-250°. Their results for this region are shown in Figure 3c, together with the beam pattern for their double-switching scheme. It appears, by eye, that there are some regions which have the signature of the beam and are therefore likely sky signals. A maximum likelihood analysis indicates that fluctuations of astronomical origin were indeed detected. The maximum likelihood was a factor ten greater than the likelihood for zero sky variance.

Davies et al carried out analyses over a range of angular scales and found strong evidence for fluctuations in the range 8-10° FWHM. On the scale of their beam (8°.3) they found an excess standard deviation of 0.1 mK. This corresponds to DeltaT/T = 3.7 x 10-5. They pointed out that the excess variance that they had detected might well have been due to Galactic synchrotron radiation, but they believed that this contamination, plus the contamination from free-free emission, would likely be too low to account for all of the excess, and that a substantial part of the emission might have been due to microwave background radiation anisotropy.

Subsequent analyses by A. Lasenby (private communication), by the group at the University of Durham (Lawson et al 1987, Banday et al 1991, Banday & Wolfendale 1991), and by us (in preparation) have shown that the excess is in fact very largely attributable to Galactic synchrotron emission, and, therefore, that there is no strong demonstration of anisotropy in the microwave background radiation in these observations. A simulation of the effects of Galactic synchrotron emission in the Tenerife experiment carried out by Lasenby (private communication) is shown in Figure 5. Details of these simulations are given in Section 4.2. Although Galactic synchrotron emission could plausibly account for all of the fluctuations observed, it should be remembered that, until the effects of the foreground emission can be subtracted with precision, intrinsic fluctuations in the microwave background radiation at the level DeltaT/T ~ 3 x 10-5 cannot be ruled out.

Figure 5. Comparison of the Davies et al (1987) observations with predicted variations due to Galactic synchrotron emission. This study by Lasenby (private communication) shows the reconvolved observations (dashed line) and the expected 10.4 GHz fluctuations (solid line), based on observations of the Galactic synchrotron emission at 408 MHz and 1420 MHz (see text) and on known discrete sources.

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