Frequency Comparison of Fields

An obvious question which remains is whether the structure in the maps is thermal. For an interferometer, this proves non-trivial to address in the image plane, since the u-v sampling scales with frequency. A simple division of the bandpass into halves, for instance, probes not only different frequencies, but different angular scales as well.

In the maps in Figure 5 we attempt to minimize this complication by imposing a u-v cutoff to equalize the sampling at each frequency, and by deconvolving the resulting sampling function from each map. The primary beam envelope also scales with frequency, and each map has been corrected by the appropriate taper, so that these represent our best estimate of the actual sky structure at each frequency. A scatter plot of the pixels in this field demonstrates that the maps are consistent with a thermal spectrum.

 

Figure: DASI image of a single CMBR field corrected for the primary beam, imaged in two different frequency ranges, 26-31 GHz (left panel) and 31-36 GHz (center panel). The right panel shows the correlations in pixel values between the two images. The images are consistent with one another, indicating the imaged signal is thermal, as expected from the CMBR.

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