Planck 2018 results. VIII. Gravitational lensing (1807.06210v2)

Abstract: We present measurements of the cosmic microwave background (CMB) lensing potential using the final $\textit{Planck}$ 2018 temperature and polarization data. We increase the significance of the detection of lensing in the polarization maps from $5\,\sigma$ to $9\,\sigma$. Combined with temperature, lensing is detected at $40\,\sigma$. We present an extensive set of tests of the robustness of the lensing-potential power spectrum, and construct a minimum-variance estimator likelihood over lensing multipoles $8 \le L \le 400$. We find good consistency between lensing constraints and the results from the $\textit{Planck}$ CMB power spectra within the $\rm{\Lambda CDM}$ model. Combined with baryon density and other weak priors, the lensing analysis alone constrains $\sigma_8 \Omega_{\rm m}^{0.25}=0.589\pm 0.020$ ($1\,\sigma$ errors). Also combining with baryon acoustic oscillation (BAO) data, we find tight individual parameter constraints, $\sigma_8=0.811\pm0.019$, $H_0=67.9_{-1.3}^{+1.2}\,\text{km}\,\text{s}^{-1}\,\rm{Mpc}^{-1}$, and $\Omega_{\rm m}=0.303^{+0.016}_{-0.018}$. Combining with $\textit{Planck}$ CMB power spectrum data, we measure $\sigma_8$ to better than $1\,\%$ precision, finding $\sigma_8=0.811\pm 0.006$. We find consistency with the lensing results from the Dark Energy Survey, and give combined lensing-only parameter constraints that are tighter than joint results using galaxy clustering. Using $\textit{Planck}$ cosmic infrared background (CIB) maps we make a combined estimate of the lensing potential over $60\,\%$ of the sky with considerably more small-scale signal. We demonstrate delensing of the $\textit{Planck}$ power spectra, detecting a maximum removal of $40\,\%$ of the lensing-induced power in all spectra. The improvement in the sharpening of the acoustic peaks by including both CIB and the quadratic lensing reconstruction is detected at high significance (abridged).

• The paper presents Planck’s final analysis using combined temperature and polarization data, significantly improving lensing detection to 9σ and 40σ.
• It introduces improved filtering techniques and robustness tests, extending the accuracy of the lensing-potential power spectrum for cosmological evaluation.
• The study robustly constrains ΛCDM parameters and enhances delensing efforts, paving the way for advanced CMB and large-scale structure studies.

Overview of Planck 2018 Lensing Results

The Planck 2018 paper on gravitational lensing presents the final analysis of the cosmic microwave background (CMB) lensing potential using the Planck data. The paper is significant due to its meticulous measurements of the lensing potential, integrating both temperature and polarization data. The paper meticulously outlines the methodology employed, introduces improvements over previous analyses, and discusses the implications of the findings in terms of cosmological parameters.

The analysis enhances the detection significance of lensing from Planck's polarization maps from 5σ to 9σ and demonstrates lensing detection at 40σ significance when combining temperature data. It introduces comprehensive robustness tests for the lensing-potential power spectrum and employs a minimum-variance estimator covering lensing multipoles from 8 to 400, which extends the range achieved in the 2015 analysis.

Integration of the lensing data with cosmological models reveals good consistency within the standard ΛCDM model. Furthermore, they derive strong constraints on cosmological parameters, notably determining that the combination σ_8Ω_m^0.25 = 0.589 ± 0.020 using lensing analysis alone, which is further refined with the inclusion of baryon acoustic oscillation (BAO) data, leading to robust individual parameter estimates such as σ_8 = 0.811 ± 0.019.

The paper's methodological strides involve advanced filtering techniques to account for noise anisotropy in polarization maps, achieving considerable gains in signal detection. In particular, the Planck CIB maps provide a unique lensing potential estimate over 60% of the sky, enhancing small-scale signal detection, pivotal for delensing operations.

The impact of delensing, which achieves the removal of up to 40% of lensing-induced power in CMB spectra, is outlined, highlighting the analytical gains made via joint estimation using the CIB. This offers improved sharpening of acoustic peaks, a result detected with high significance.

Addressing systematic effects, the paper presents consistency tests and speculates on potential biases, such as those arising from non-Gaussianity of the lensing field. Critically, the report also emphasizes potential systematic errors, like those indicated by the negative curl feature observed in the high-L range of the lensing spectrum, prompting a conservative finishing range in their primary cosmological analyses.

The provided outcomes deliver crucial implications, particularly in refining large-scale structure studies and aiding future CMB analyses in adopting more refined delensing techniques. The joint datasets offered by Planck serve as a reference for large-scale testing of both existing and novel theoretical models within cosmology.

Lastly, the paper's open release of its data products—from the lensing maps and simulations to likelihoods and parameter tables—bears significant academic utility, essential for ongoing and future cross-correlation studies and extending the frontiers of cosmological research.