and Cosmology

8.6 Angular Fluctuations of the Cosmic Microwave Background
343
Fig. 8.27. In 2000, two groups published the results of their
CMB observations, BOOMERANG and MAXIMA. This
figure shows the BOOMERANG data. On the left, the temperature
distributions at 90 GHz, 150 GHz, and 240 GHz are
displayed, while the lower right panel shows that at 400 GHz.
The three small circles in each panel denote the location of
known strong point sources. The two upper panels on the right
show the differences of temperature maps obtained at two different
frequencies, e.g., the temperature map obtained with
the 90-GHz data minus that obtained from the 150-GHz data.
These difference maps feature considerably smaller fluctuations
than the individual maps. This is compatible with the
idea that the major fraction of the radiation originates in the
CMB and not, e.g., in Galactic radiation which has a different
spectral distribution and would thus be more prominent in the
difference maps. Only the region within the dashed rectangle
was used in the original analysis of the temperature fluctuations,
in order to avoid boundary effects. The fluctuation
spectrum computed from the difference maps is compatible
with pure noise
indications of the presence of the second Doppler peak
were found.
In April 2001, refined CMB anisotropy measurements
from three experiments were released,
BOOMERANG, MAXIMA, and DASI. For the former
two, the observational data were the same as in the year
before, but improved analysis methods were applied;
in particular, a better instrumental calibration was obtained.
The resulting temperature fluctuation spectrum
is presented in Fig. 8.28, demonstrating that it was now
possible to determine the locations of the first three
Doppler peaks.
The status of measurements of the CMB anisotropy
as of the end of 2002 is shown in Fig. 8.29. In the lefthand
panel, the results of numerous experiments are
plotted individually. The panel on the right shows the
weighted mean of these experiments. Although it might
not be suspected at first sight, the results of all experiments
shown on the left are compatible with each
other. With that we mean that the individual measure-