The Atacama Cosmology Telescope: Measurement and Analysis of 1D Beams for DR4

• Published in: arXiv.org
• Main Authors: Lungu, Marius, Storer, Emilie R, Hasselfield, Matthew, Duivenvoorden, Adriaan J, Calabrese, Erminia, Chesmore, Grace E, Choi, Steve K, Dunkley, Jo, Dünner, Rolando, Gallardo, Patricio A, Golec, Joseph E, Guan, Yilun, Hill, J Colin, Hincks, Adam D, Hubmayr, Johannes, Madhavacheril, Mathew S, Mallaby-Kay, Maya, McMahon, Jeff, Moodley, Kavilan, Naess, Sigurd, Nati, Federico, Niemack, Michael D, Page, Lyman A, Partridge, Bruce, Puddu, Roberto, Schillaci, Alessandro, Sifón, Cristóbal, Staggs, Suzanne, Sunder, Dhaneshwar D, Wollack, Edward J, Xu, Zhilei
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 17.02.2022
• Subjects: Atmospheric effects; Cosmology; Leakage; Physics - Cosmology and Nongalactic Astrophysics; Physics - Instrumentation and Methods for Astrophysics; Polarization; Power spectrum analysis; Sidelobes; Subtraction; Telescopes; Uranus
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2112.12226

We describe the measurement and treatment of the telescope beams for the Atacama Cosmology Telescope's fourth data release, DR4. Observations of Uranus are used to measure the central portion (<12') of the beams to roughly -40 dB of the peak. Such planet maps in intensity are used to construct azimuthally averaged beam profiles, which are fit with a physically motivated model before being transformed into Fourier space. We investigate and quantify a number of percent-level corrections to the beams, all of which are important for precision cosmology. Uranus maps in polarization are used to measure the temperature-to-polarization leakage in the main part of the beams, which is <1% (2.5%) at 150 GHz (98 GHz). The beams also have polarized sidelobes, which are measured with observations of Saturn and deprojected from the ACT time-ordered data. Notable changes relative to past ACT beam analyses include an improved subtraction of the atmospheric effects from Uranus calibration maps, incorporation of a scattering term in the beam profile model, and refinements to the beam model uncertainties and the main temperature-to-polarization leakage terms in the ACT power spectrum analysis.