A DETAILED DESCRIPTION OF THE CAMSPEC LIKELIHOOD PIPELINE AND A REANALYSIS OF THE PLANCK HIGH FREQUENCY MAPS

Abstract

This paper presents a detailed description of the CamSpec likelihood which has been used to analyse Planck temperature and polarization maps of the cosmic microwave background since the first Planck data release. The goal of the CamSpec pipeline has been to extract an accurate likelihood based on the TT, TE and EE spectra from Planck which can be used to test cosmological models. Planck is an important legacy dataset which is likely to be reanalysed by many researchers for many years to come. Our aim in this paper is to present, in a single source, a comprehensive analysis of our methodology including what we have learned about: (a) the CMB sky and associated foregrounds at the Planck high frequencies (ν ≥ 100 GHz); (b) the consistency of the Planck data in temperature and polarization; (c) experimental systematics in the Planck data which need to be corrected when building a likelihood. For this paper we have created a number of temperature and polarization likelihoods using a range of Galactic sky masks and different methods of temperature foreground cleaning. Our most powerful likelihood uses 80% of the sky in temperature and polarization at 143 and 217 GHz, increasing the effective sky coverage compared to the likelihoods used in the 2018 Planck data release. Our results show that the base six-parameter ΛCDM cosmology provides an excellent fit to the Planck data. There is no evidence for statistically significant internal tensions in the Planck TT, TE and EE spectra computed for different frequency combinations. The cosmological parameters of the base ΛCDM model are entirely consistent with those reported by the Planck collaboration in [1] and earlier Planck papers, though our most powerful likelihood tightens up the statistical uncertainties and reduces the residuals of the TT, TE and EE spectra relative to the best fit model. We present evidence that the tendencies for the Planck temperature power spectra to favour a lensing amplitude AL > 1 and positive spatial curvature Ωk < 0 reported in [1] are caused by statistical fluctuations in the temperature power spectra in the multipole range 800 ∼ < 1600, which are repeatable between detectors and frequencies. Using our statistically most powerful likelihood, combined with the 2018 Planck low multipole likelihoods for ℓ < 30, we find that the AL parameter determined from the Planck power spectra alone differs from unity at no more than the 2.2σ level. We find no evidence for anomalous shifts of cosmological parameters with multipole range. In fact, we show that the combined TTTEEE CamSpec likelihood over the restricted multipole range 2 ≤ ℓ ≤ 800 gives cosmological parameters for the base ΛCDM cosmology that are very close to those derived from the full multipole range 2 ≤ ℓ ≤ 2500. We present revised constraints on a few extensions of the base ΛCDM cosmology, focussing on the sum of neutrino masses, the number of relativistic species and the tensor-scalar ratio. The results presented here show that the Planck data are remarkably consistent between detectorsets, frequencies and sky area. We find no evidence in our analysis that cosmological parameters determined from the CamSpec likelihood are affected to any significant degree by systematic errors in the Planck data.