BEYONDPLANCK

VIII. Efficient sidelobe convolution and corrections through spin harmonics

¹ Institute of Theoretical Astrophysics, University of Oslo, Blindern, Oslo, Norway
e-mail: mathew.galloway@astro.uio.no
² Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
³ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria, 16, Milano, Italy
⁴ INAF-IASF Milano, Via E. Bassini 15, Milano, Italy
⁵ INFN, Sezione di Milano, Via Celoria 16, Milano, Italy
⁶ INAF – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, Trieste, Italy
⁷ Planetek Hellas, Leoforos Kifisias 44, Marousi, 151 25 Greece
⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, 08544 USA
⁹ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA
¹⁰ Department of Physics, Gustaf Hällströmin katu 2, University of Helsinki, Helsinki, Finland
¹¹ Helsinki Institute of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
¹² Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
¹³ Haverford College Astronomy Department, 370 Lancaster Avenue, Haverford, PA, USA
¹⁴ Dipartimento di Fisica, Università degli Studi di Trieste, Via A. Valerio 2, Trieste, Italy

Received: 17 January 2022
Accepted: 18 March 2022

Abstract

We introduce a new formulation of the Conviqt convolution algorithm in terms of spin harmonics, and apply this to the problem of sidelobe correction for BEYONDPLANCK, the first end-to-end Bayesian Gibbs sampling framework for CMB analysis. We compare our implementation to the previous Planck LevelS implementation, and find good agreement between the two codes in terms of accuracy, but with a speed-up reaching a factor of 3–10, depending on the frequency bandlimits, l_max and m_max. The new algorithm is significantly simpler to implement and maintain, since all low-level calculations are handled through an external spherical harmonic transform library. We find that our mean sidelobe estimates for Planck LFI are in good agreement with previous efforts. Additionally, we present novel sidelobe rms maps that quantify the uncertainty in the sidelobe corrections due to variations in the sky model.