Proceedings of the Particle Physics and Early Universe Conference (PPEUC).
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4 Analysis 

To confirm the detection of CMB anisotropy in the CAT2 field statistically, a Bayesian maximum-likelihood analysis (Hobson et al. (1995)) was performed on the raw complex visibilities, which were split first into two bins of low and high . CMB and Galactic signals were modelled as independent Gaussian distributions, the CMB with a fixed spectral index of 2 in flux density and the Galactic spectral index variable between 0 and 1. After marginalising over the Galactic parameters, this analysis confirmed that the bulk of the power in the 16.5 GHz map is due to CMB signal, with relative amplitudes in the two bins of and centred on (spherical harmonic) multipoles and respectively.

These values of in the CAT2 field are slightly lower than found in CAT1 but fall within the error bars, consistent with sample variance. The good agreement between the two independent measurements in two different patches of sky reinforces the impact of the CAT points on the power spectrum, and together with other data on larger scales, clearly marks the presence of the first Doppler peak.

Figure 1:  16.5 GHz CAT image of area centred on the CAT2 field, after discrete sources have been subtracted. Excess power can be seen in the central primary beam (because the sensitivity drops sharply outside this area, the outer regions are a good indicator of the noise level on the map). The flux density range scale spans mJy per beam.

PPEUC Proceedings
Fri Jul 25 11:29:49 BST 1997