Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A First Detection of Atmospheric Circular Polarization at Q band
Date
2020-02-01Author
Petroff, Matthew A.
Eimer, Joseph R.
Harrington, Kathleen
Ali, Aamir
Appel, John W.
Bennett, Charles L.
Brewer, Michael K.
Bustos Placencia, Ricardo
Chan, Manwei
Chuss, David T.
Cleary, Joseph
Denes Couto, Jullianna
Dahal, Sumit
Dünner, Rolando
Essinger-Hileman, Thomas
Fluxá Rojas, Pedro
Gothe, Dominik
Iuliano, Jeffrey
Marriage, Tobias A.
Miller, Nathan J.
Núñez, Carolina
Padilla, Ivan L.
Parker, Lucas
Reeves, Rodrigo
Rostem, Karwan
Nunes Valle, Deniz Augusto
Watts, Duncan J.
Weiland, Janet L.
Wollack, Edward J.
Xu, Zhilei
Publisher
Astrophysical JournalDescription
Metadata
Show full item recordAbstract
The Earth’s magnetic field induces Zeeman splitting of the magnetic dipole transitions of molecular oxygen in the
atmosphere, which produces polarized emission in the millimeter-wave regime. This polarized emission is
primarily circularly polarized and manifests as a foreground with a dipole-shaped sky pattern for polarizationsensitive ground-based cosmic microwave background experiments, such as the Cosmology Large Angular Scale
Surveyor (CLASS), which is capable of measuring large angular scale circular polarization. Using atmospheric
emission theory and radiative transfer formalisms, we model the expected amplitude and spatial distribution of this
signal and evaluate the model for the CLASS observing site in the Atacama Desert of northern Chile. Then, using
two years of observations at 32°. 3 to 43.7 GHz from the CLASS Q-band telescope, we present a detection of this
signal and compare the observed signal to that predicted by the model. We recover an angle between magnetic
north and true north of −5°. 5 ± 0°. 6, which is consistent with the expectation of −5°.9 for the CLASS observing
site. When comparing dipole sky patterns fit to both simulated and data-derived sky maps, the dipole directions
match to within a degree, and the measured amplitudes match to within ∼20%.