Background on 20 GHz channel
This posting summarizes the analyses that led to the decision to move the 20 GHz channel from the SATs to the delensing LAT.
During the CDT studies, we noticed a bias on r for one of the foreground models for the configuration under study at the time. The configuration was not designated with an official data challenge number. It can either be thought of as the configuration obtained from configuration 02 by rescaling by a factor sqrt(7/6), or equivalently as configuration 04 but with a 20 GHz channel on the SATs rather than the delensing LAT. For completeness, here is the performance table
|Beam FWHM (arcmin)||76.6||76.6||57.5||27.0||24.2||15.9||14.8||10.7||8.5|
|white noise level TT (uK-arcmin)||16.66||10.62||10.07||2.01||1.59||4.53||4.53||11.61||15.84|
|ell knee TT||500||175||175||175||175||230||230||230||230|
|1/f exponent TT||-4.1||-4.1||-4.1||-4.1||-4.1||-3.8||-3.8||-3.8||-3.8|
|white noise level EE (uK-arcmin)||13.94||8.88||8.42||1.67||1.32||2.12||2.12||5.43||7.42|
|ell knee EE||200||50||50||50||50||65||65||65||65|
|1/f exponent EE||-2.0||-2.0||-2.0||-2.0||-2.0||-3.0||-3.0||-3.0||-3.0|
|white noise level BB (uK-arcmin)||13.6||8.67||8.22||1.64||1.30||2.03||2.03||5.19||7.08|
|ell knee BB||200||50||50||50||50||60||60||60||60|
|1/f exponent BB||-2.0||-2.0||-2.0||-2.0||-2.0||-3.0||-3.0||-3.0||-3.0|
The foreground model that displayed the bias was model 06, which is based on MHD simulations of the ISM.
Closer inspection of the ILC results revealed that the bias was caused by synchrotron residuals in bins 4-6. This can be seen in the figure below. The blue points and error bars indicate the ILC spectrum, green data points show the dust residuals, red data points show the synchrotron residuals.
Comparison the noise power to power in synchrotron radiation, it is natural to suspect that this is caused by the large beam at low frequencies
This motivated a study of the bias as a function of beam size at low frequency. A number of configurations were studied. I will show the most relevant subset, and refer to the configurations by my internal configuration numbers.