BEYONDPLANCK: I. Global Bayesian analysis of the Planck Low Frequency Instrument data

K. J. Andersen, R. Aurlien, Elina Keihänen, R. Keskitalo, Anna-Stiina Suur-Uski

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We describe the BeyondPlanck project in terms of our motivation, methodology, and main products, and provide a guide to a set of companion papers that describe each result in more detail. Building directly on experience from ESA's Planck mission, we implemented a complete end-to-end Bayesian analysis framework for the Planck Low Frequency Instrument (LFI) observations. The primary product is a full joint posterior distribution P( omega vertical bar d), where omega represents the set of all free instrumental (gain, correlated noise, bandpass, etc.), astrophysical (synchrotron, free-free, thermal dust emission, etc.), and cosmological (cosmic microwave background - CMB - map, power spectrum, etc.) parameters. Some notable advantages of this approach compared to a traditional pipeline procedure are seamless end-to-end propagation of uncertainties; accurate modeling of both astrophysical and instrumental e ffects in the most natural basis for each uncertain quantity; optimized computational costs with little or no need for intermediate human interaction between various analysis steps; and a complete overview of the entire analysis process within one single framework. As a practical demonstration of this framework, we focus in particular on low-l CMB polarization reconstruction with Planck LFI. In this process, we identify several important new e ffects that have not been accounted for in previous pipelines, including gain oversmoothing and time-variable and non-1/f correlated noise in the 30 and 44 GHz channels. Modeling and mitigating both previously known and newly discovered systematic e ffects, we find that all results are consistent with the Lambda CDM model, and we constrained the reionization optical depth to tau = 0:066 +/- 0:013, with a low-resolution CMB-based X-2 probability to exceed of 32%. This uncertainty is about 30% larger than the o fficial pipelines, arising from taking a more complete instrumental model into account. The marginal CMB solar dipole amplitude is 3362.7 +/- 1.4 mu K, where the error bar was derived directly from the posterior distribution without the need of any ad hoc instrumental corrections. We are currently not aware of any significant unmodeled systematic e ffects remaining in the Planck LFI data, and, for the first time, the 44 GHz channel is fully exploited in the current analysis. We argue that this framework can play a central role in the analysis of many current and future high-sensitivity CMB experiments, including LiteBIRD, and it will serve as the computational foundation of the emerging community-wide Cosmoglobe e ffort, which aims to combine state-of-the-art radio, microwave, and submillimeter data sets into one global astrophysical model.
Original languageEnglish
Article numberA1
JournalAstronomy & Astrophysics
Number of pages61
Publication statusPublished - Jul 2023
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 115 Astronomy, Space science
  • 114 Physical sciences

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