Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A First Detection of Atmospheric Circular Polarization at Q Band

Abstract

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 polarization-sensitive 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 GHz 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 $(-5.5\pm 0.6{)}^{\circ }$, which is consistent with the expectation of $-5.9^{\circ }$ 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 $\sim 20\%$.

13 pages, 7 figures, published in ApJ

References in corpus (26)

• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The Temperature of the Cosmic Microwave Background
• CLASS: The Cosmology Large Angular Scale Surveyor
• Systematic errors in cosmic microwave background polarization measurements
• The Cosmology Large Angular Scale Surveyor
• Generation of circular polarization of the CMB
• The Cosmology Large Angular Scale Surveyor (CLASS): 40 GHz optical design
• Properties of a Variable-delay Polarization Modulator
• Results from the Atacama B-mode Search (ABS) Experiment
• A New Limit on CMB Circular Polarization from SPIDER
• A Projected Estimate of the Reionization Optical Depth Using the CLASS Experiment's Sample-Variance Limited E-Mode Measurement
• Evidence for cosmic neutrino background form CMB circular polarization
• The V-mode polarization of the Cosmic Microwave Background
• An improved upper limit to the CMB circular polarization at large angular scales
• Circular polarization of the CMB: Foregrounds and detection prospects
• Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A Measurement of Circular Polarization at 40 GHz
• On-sky performance of the CLASS Q-band telescope
• Circular polarization of the cosmic microwave background from vector and tensor perturbations
• Measuring the Largest Angular Scale CMB B-mode Polarization with Galactic Foregrounds on a Cut Sky
• Measurements of tropospheric ice clouds with a ground-based CMB polarization experiment, POLARBEAR
• A template of atmospheric O2 circularly polarized emission for CMB experiments
• Observing CMB polarisation through ice

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• Introductory Notes on Non-linear Electrodynamics and its Applications
• Four-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: On-sky Receiver Performance at 40, 90, 150, and 220 GHz Frequency Bands
• Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance
• Two Year Cosmology Large Angular Scale Surveyor (CLASS) Observations: Long Timescale Stability Achieved with a Front-End Variable-delay Polarization Modulator at 40 GHz
• The Atacama Cosmology Telescope: Modeling Bulk Atmospheric Motion
• Measurement and Modeling of Polarized Atmosphere at the South Pole with SPT-3G
• Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance
• The Simons Observatory: Validation of reconstructed power spectra from simulated filtered maps for the Small Aperture Telescope survey
• The Atacama Cosmology Telescope: Quantifying Atmospheric Emission above Cerro Toco
• Characterization of a half-wave plate for cosmic microwave background circular polarization measurement with POLARBEAR
• A measurement of atmospheric circular polarization with POLARBEAR