BeyondPlanck X. Planck LFI frequency maps with sample-based error propagation

Abstract

We present Planck LFI frequency sky maps derived within the BeyondPlanck framework. This framework draws samples from a global posterior distribution that includes instrumental, astrophysical and cosmological parameters, and the main product is an entire ensemble of frequency sky map samples. This ensemble allows for computationally convenient end-to-end propagation of low-level instrumental uncertainties into higher-level science products. We show that the two dominant sources of LFI instrumental systematic uncertainties are correlated noise and gain fluctuations, and the products presented here support - for the first time - full Bayesian error propagation for these effects at full angular resolution. We compare our posterior mean maps with traditional frequency maps delivered by the Planck collaboration, and find generally good agreement. The most important quality improvement is due to significantly lower calibration uncertainties in the new processing, as we find a fractional absolute calibration uncertainty at 70 GHz of $\delta g_0/g_0=5\cdot 10^{-5}$, which is nominally 40 times smaller than that reported by Planck 2018. However, the original Planck 2018 estimate has a non-trivial statistical interpretation, and this further illustrates the advantage of the new framework in terms of producing self-consistent and well-defined error estimates of all involved quantities without the need of ad hoc uncertainty contributions. We describe how low-resolution data products, including dense pixel-pixel covariance matrices, may be produced directly from the posterior samples without the need for computationally expensive analytic calculations or simulations. We conclude that posterior-based frequency map sampling provides unique capabilities in terms of low-level systematics modelling and error propagation, and may play an important role for future CMB B-mode experiments. (Abridged.)

32 pages, 23 figures, data available from https://www.cosmoglobe.uio.no/

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• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• Making Maps from Planck LFI 30GHz Data
• Planck-LFI radiometers' spectral response
• BeyondPlanck XII. Cosmological parameter constraints with end-to-end error propagation
• BeyondPlanck XI. Bayesian CMB analysis with sample-based end-to-end error propagation
• BeyondPlanck IV. On end-to-end simulations in CMB analysis -- Bayesian versus frequentist statistics
• Polarization and variability of compact sources measured in Planck time-ordered data

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• Cosmoglobe DR1 results. I. Improved Wilkinson Microwave Anisotropy Probe maps through Bayesian end-to-end analysis
• BeyondPlanck XI. Bayesian CMB analysis with sample-based end-to-end error propagation
• BeyondPlanck IV. On end-to-end simulations in CMB analysis -- Bayesian versus frequentist statistics
• Optimal bolometer transfer function deconvolution for CMB experiments through maximum likelihood mapmaking