The Atacama Cosmology Telescope: Quantifying Atmospheric Emission above Cerro Toco
astro-ph.IM
/ Authors
Thomas W. Morris, Elia Battistelli, Ricardo Bustos, Steve K. Choi, Adriaan J. Duivenvoorden, Jo Dunkley, Rolando Dünner, Mark Halpern, Yilun Guan, Joshiwa van Marrewijk
and 10 more authors
Tony Mroczkowski, Sigurd Naess, Michael D. Niemack, Lyman A. Page, Bruce Partridge, Roberto Puddu, Maria Salatino, Cristóbal Sifón, Yuhan Wang, Edward J. Wollack
/ Abstract
At frequencies below 1 Hz, fluctuations in atmospheric emission in the Chajnantor region in northern Chile are the primary source of interference for bolometric millimeter-wave observations. This paper focuses on characterizing these fluctuations using measurements from the Atacama Cosmology Telescope (ACT) and the Atacama Pathfinder Experiment (APEX) water vapor radiometer. We show that the total precipitable water vapor (PWV) is not in general an accurate estimator of the level of fluctuations in millimeter-wave atmospheric emission. We also show that the microwave frequency spectrum of atmospheric fluctuations is in good agreement with predictions by the am code for frequency bands above 90 GHz. We introduce a new method for separating atmospheric and systematic fluctuations, allowing us to fit a robust atmospheric flatfield, as well as to study in the atmosphere in greater detail than previous works. We present a direct measurement of the temporal outer scale of turbulence of $τ_0\approx50$ s corresponding to a spatial scale of $L_0\approx500$ m. Lastly, we show the variance of fluctuations in ACT's mm-wave bands correlate with the variance of fluctuations in PWV measured by APEX, even though the observatories are $6$ km apart and observe different lines of sight.