The Simons Observatory: Quantifying the impact of beam chromaticity on large-scale <i>B</i>-mode science

Abstract The Simons Observatory (SO) Small Aperture Telescopes (SATs) will observe the Cosmic Microwave Background (CMB) temperature and polarization at six frequency bands. Within these bands, the angular response of the telescope (beam) is convolved with the instrument's spectral response (commonly called bandpass) and the signal from the sky, which leads to the band-averaged telescope beam response, which is sampled and digitized. The spectral properties of the band-averaged beam depend on the natural variation of the beam within the band, referred to as beam chromaticity. In this paper, we quantify the impact of the interplay of beam chromaticity and intrinsic frequency scaling from the various components that dominate the polarized sky emission on the tensor-to-scalar ratio, r , and foreground parameters. We do so by employing a parametric power-spectrum-based foreground component separation algorithm, namely BBPower , to which we provide beam-convolved time domain simulations performed with the beamconv software while assuming an idealized version of the SO SAT optics. We find a small, 0.02 σ , bias on r , due to beam chromaticity, which seems to mostly impact the dust spatial parameters, causing a maximum 0.77 σ bias on the dust B -mode spectra amplitude, A d , when employing Gaussian foreground simulations. However, we find all parameter biases to be smaller than 1 σ at all times, independently of the foreground model. This includes the case where we introduce additional uncertainty on the bandpass shape, which accounts for approximately half of the total allowed gain uncertainty, as estimated in previous work for the SO SATs.

Authors

Institutions

Publication Details

Journal
Journal of Cosmology and Astroparticle Physics
Published
2025-10-01
DOI
https://doi.org/10.1088/1475-7516/2025/10/005
Primary Topic
Cosmology and Gravitation Theories
Type
article
Field-Weighted Citation Impact
0.00
Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

The Simons Observatory: Quantifying the impact of beam chromaticity on large-scale B-mode science

Jon E. Gudmundsson, C. Baccigalupi, Nicholas Galitzki, Yoshinori Sueno et al.
Journal of Cosmology and Astroparticle Physics
Cosmology and Gravitation Theories
article

The Simons Observatory: Quantifying the impact of beam chromaticity on large-scale B-mode science

Jon E. Gudmundsson, C. Baccigalupi, Nicholas Galitzki, Yoshinori Sueno, Carlos Hervías-Caimapo, Nadia Dachlythra, Remington G. Gerras, A. Carones, Alexandre Adler, M. Gerbino, Selim C. Hotinli, Adriaan J. Duivenvoorden, David Alonso, Gabriele Coppi, Samuel Day-Weiss, F. Nati, Bruce Partridge, S. Azzoni, Josquin Errard, Edward J. Wollack, Kevin Wolz
article en

Abstract

Abstract The Simons Observatory (SO) Small Aperture Telescopes (SATs) will observe the Cosmic Microwave Background (CMB) temperature and polarization at six frequency bands. Within these bands, the angular response of the telescope (beam) is convolved with the instrument's spectral response (commonly called bandpass) and the signal from the sky, which leads to the band-averaged telescope beam response, which is sampled and digitized. The spectral properties of the band-averaged beam depend on the natural variation of the beam within the band, referred to as beam chromaticity. In this paper, we quantify the impact of the interplay of beam chromaticity and intrinsic frequency scaling from the various components that dominate the polarized sky emission on the tensor-to-scalar ratio, r , and foreground parameters. We do so by employing a parametric power-spectrum-based foreground component separation algorithm, namely BBPower , to which we provide beam-convolved time domain simulations performed with the beamconv software while assuming an idealized version of the SO SAT optics. We find a small, 0.02 σ , bias on r , due to beam chromaticity, which seems to mostly impact the dust spatial parameters, causing a maximum 0.77 σ bias on the dust B -mode spectra amplitude, A d , when employing Gaussian foreground simulations. However, we find all parameter biases to be smaller than 1 σ at all times, independently of the foreground model. This includes the case where we introduce additional uncertainty on the bandpass shape, which accounts for approximately half of the total allowed gain uncertainty, as estimated in previous work for the SO SATs.

Journal of Cosmology and Astroparticle PhysicsVol. 2025(10)
University of Southern California (US), Centre National de la Recherche Scientifique (FR), Goddard Space Flight Center (US), Scuola Internazionale Superiore di Studi Avanzati (IT), Lawrence Berkeley National Laboratory (US), Haverford College (US), Istituto Nazionale di Fisica Nucleare (IT), Stockholm University (SE), Pontificia Universidad Católica de Chile (CL), University of Iceland (IS), Perimeter Institute (CA), Princeton University (US), Université Paris Cité (FR), Laboratoire AstroParticule et Cosmologie (FR), University of Oxford (GB), Max Planck Institute for Astrophysics (DE), Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara (IT), Instituto de Física Teórica (ES), AlbaNova (SE), Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Trieste (IT), Institute for Fundamental Physics of the Universe (IT), University of Milano-Bicocca (IT), The University of Texas at Austin (US), University of California, Berkeley (US)
Openalex Percentile: Top 81%
Cosmology and Gravitation Theories
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.