BEYONDPLANCK. X. Planck Low Frequency Instrument frequency maps with samplebased error propagation
Abstract
We present Planck Low Frequency Instrument (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, each of which corresponds to one possible realization of the various modeled instrumental systematic corrections, including correlated noise, timevariable gain, as well as far sidelobe and bandpass corrections. This ensemble allows for computationally convenient endtoend propagation of lowlevel instrumental uncertainties into higherlevel science products, including astrophysical component maps, angular power spectra, and cosmological parameters. 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 compared 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 Δg_{0}/g_{0} = 5 × 10^{−5}, which is nominally 40 times smaller than that reported by Planck 2018. However, we also note that the original Planck 2018 estimate has a nontrivial statistical interpretation, and this further illustrates the advantage of the new framework in terms of producing selfconsistent and welldefined error estimates of all involved quantities without the need of ad hoc uncertainty contributions. We describe how lowresolution data products, including dense pixelpixel covariance matrices, may be produced from the posterior samples directly, without the need for computationally expensive analytic calculations or simulations. We conclude that posteriorbased frequency map sampling provides unique capabilities in terms of lowlevel systematics modeling and error propagation, and may play an important role for future Cosmic Microwave Background (CMB) Bmode experiments aiming at nanokelvin precision.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 July 2023
 DOI:
 10.1051/00046361/202244819
 arXiv:
 arXiv:2208.14293
 Bibcode:
 2023A&A...675A..10B
 Keywords:

 ISM: general;
 cosmology: observations;
 diffuse radiation;
 Galaxy: general;
 cosmic background radiation;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 32 pages, 23 figures, data available from https://www.cosmoglobe.uio.no/