The Simons Observatory: Pipeline comparison and validation for large-scale B-modes

¹ International School for Advanced Studies (SISSA), Via Bonomea 265, 34136 Trieste, Italy
e-mail: kevin.wolz93@gmail.com
² National Institute for Nuclear Physics (INFN) – Sezione di Trieste, Via Valerio 2, 34127 Trieste, Italy
³ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁴ Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
⁵ Department of Physics, Florida State University, Tallahassee, Florida 32306, USA
⁶ Instituto de Astrofísica and Centro de Astro-Ingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
⁷ Université Paris Cité, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁸ Institute for Fundamental Physics of the Universe (IFPU), Via Beirut 2, 34151 Grignano (TS), Italy
⁹ Berkeley Center for Cosmological Physics, Department of Physics, University of California, Berkeley, CA 94720, USA
¹⁰ Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA
¹¹ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M20 4PE, UK
¹² School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, Wales CF24 3AA, UK
¹³ Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, 10010 New York, NY, USA
¹⁴ Department of Physics, University of Texas at Austin, Austin, Texas 78722, USA
¹⁵ Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU,WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
¹⁶ Department of Physics, University of Milano-Bicocca, Piazza della Scienza 3, 20126 Milan, Italy
¹⁷ Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA
¹⁸ Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA
¹⁹ CNRS-UCB International Research Laboratory, Centre Pierre Binétruy, IRL2007, CPB-IN2P3, Berkeley, USA

Received: 8 February 2023
Accepted: 5 March 2024

Abstract

Context. The upcoming Simons Observatory Small Aperture Telescopes aim at achieving a constraint on the primordial tensor-to-scalar ratio r at the level of σ(r = 0)≲0.003, observing the polarized CMB in the presence of partial sky coverage, cosmic variance, inhomogeneous non-white noise, and Galactic foregrounds.

Aims. We present three different analysis pipelines able to constrain r given the latest available instrument performance, and compare their predictions on a set of sky simulations that allow us to explore a number of Galactic foreground models and elements of instrumental noise, relevant for the Simons Observatory.

Methods. The three pipelines employ different combinations of parametric and non-parametric component separation at the map and power spectrum levels, and use B-mode purification to estimate the CMB B-mode power spectrum. We applied them to a common set of simulated realistic frequency maps, and compared and validated them with focus on their ability to extract robust constraints on the tensor-to-scalar ratio r. We evaluated their performance in terms of bias and statistical uncertainty on this parameter.

Results. In most of the scenarios the three methodologies achieve similar performance. Nevertheless, several simulations with complex foreground signals lead to a > 2σ bias on r if analyzed with the default versions of these pipelines, highlighting the need for more sophisticated pipeline components that marginalize over foreground residuals. We show two such extensions, using power-spectrum-based and map-based methods, that are able to fully reduce the bias on r below the statistical uncertainties in all foreground models explored, at a moderate cost in terms of σ(r).