Kavli Affiliate: Chao-Lin Kuo
| First 5 Authors: A. Coerver, J. A. Zebrowski, S. Takakura, W. L. Holzapfel, P. A. R. Ade
| Summary:
We present the detection and characterization of fluctuations in linearly
polarized emission from the atmosphere above the South Pole. These measurements
make use of data from the SPT-3G receiver on the South Pole Telescope in three
frequency bands centered at 95, 150, and 220 GHz. We use the cross-correlation
between detectors to produce an unbiased estimate of the power in Stokes I, Q,
and U parameters on large angular scales. Our results are consistent with the
polarized signal being produced by the combination of Rayleigh scattering of
thermal radiation from the ground and thermal emission from a population of
horizontally aligned ice crystals with an anisotropic distribution described by
Kolmogorov turbulence. The measured spatial scaling, frequency scaling, and
elevation dependence of the polarized emission are explained by this model.
Polarized atmospheric emission has the potential to significantly impact
observations on the large angular scales being targeted by searches for
inflationary B-mode CMB polarization. We present the distribution of measured
angular power spectrum amplitudes in Stokes Q and I for 4 yr of Austral winter
observations, which can be used to simulate the impact of atmospheric
polarization and intensity fluctuations at the South Pole on a specified
experiment and observation strategy. We present a mitigation strategy that
involves both downweighting significantly contaminated observations and
subtracting a polarized atmospheric signal from the 150 GHz band maps. In
observations with the SPT-3G instrument, the polarized atmospheric signal is a
well-understood and subdominant contribution to the measured noise after
implementing the mitigation strategies described here.
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