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 does not have a 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 convenience, 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.