# Planck intermediate results: LI. Features in the cosmic microwave background temperature power spectrum and shifts in cosmological parameters

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### Researchers

### Research units

- Université Paris-Sud
- Leiden University
- University of Oslo
- University of Cambridge
- Kavli Institute for Cosmology Cambridge
- International School for Advanced Studies
- University of Bologna
- Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna
- National Institute for Nuclear Physics
- CNRS
- Université de Toulouse
- CSIC
- University of Padova
- Indian Institute of Science Education and Research Thiruvananthapuram
- Sorbonne Université
- University of Milan
- Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences
- University of Manchester
- University of Oviedo
- University of Toronto
- Lawrence Berkeley National Laboratory
- University of California at Berkeley
- Universite Paris Sorbonne - Paris IV
- University of Ferrara
- Cardiff University
- Observatoire de Paris
- Télécom Paris
- University of KwaZulu-Natal
- Princeton University
- University of Southern California
- Jet Propulsion Laboratory, California Institute of Technology
- Université Grenoble Alpes
- California Institute of Technology
- University of Rome La Sapienza
- Astronomical Observatory of Padua
- Imperial College London
- European Space Astronomy Centre
- Max Planck Institute for Astrophysics
- African Institute for Mathematical Sciences
- University of Stellenbosch
- Osservatorio Astronomico di Trieste
- Simon Fraser University
- University of Chicago
- University of La Laguna
- Instituto Astrofisico de Canarias
- NORDITA
- Stockholm University
- University of Warsaw
- Sun Yat-Sen University
- University of Helsinki
- University of California at Davis
- University of Geneva
- University of Sussex
- University of California at Santa Barbara
- Jodrell Bank Centre for Astrophysics
- CAS - Purple Mountain Observatory
- School of Chemistry and Physics
- University College London
- Italian Space Agency
- University of Rome Tor Vergata
- University of Nottingham
- University of British Columbia
- Technical University of Denmark
- Haverford College
- Heidelberg University
- Radboud University Nijmegen
- University of Granada
- ESTEC
- University of Trieste
- University of Illinois at Urbana-Champaign
- University of California at San Diego

### Abstract

The six parameters of the standard ΛCDM model have best-fit values derived from the Planck temperature power spectrum that are shifted somewhat from the best-fit values derived from WMAP data. These shifts are driven by features in the Planck temperature power spectrum at angular scales that had never before been measured to cosmic-variance level precision. We have investigated these shifts to determine whether they are within the range of expectation and to understand their origin in the data. Taking our parameter set to be the optical depth of the reionized intergalactic medium, the baryon density ω_{b}, the matter density ω_{m}, the angular size of the sound horizon the spectral index of the primordial power spectrum, n_{s}, and A_{s}e^{-2τ} (where A_{s} is the amplitude of the primordial power spectrum), we have examined the change in best-fit values between a WMAP-like large angular-scale data set (with multipole moment < 800 in the Planck temperature power spectrum) and an all angular-scale data set (< 2500Planck temperature power spectrum), each with a prior on τ of 0.07 ± 0.02. We find that the shifts, in units of the 1σ expected dispersion for each parameter, are {value of 8.0. We find that this χ^{2} value is exceeded in 15% of our simulated data sets, and that a parameter deviates by more than 2.2σ in 9% of simulated data sets, meaning that the shifts are not unusually large. Comparing < 800 instead to > 800, or splitting at a different multipole, yields similar results. We examined the < 800 model residuals in the > 800 power spectrum data and find that the features there that drive these shifts are a set of oscillations across a broad range of angular scales. Although they partly appear similar to the effects of enhanced gravitational lensing, the shifts in ΛCDM parameters that arise in response to these features correspond to model spectrum changes that are predominantly due to non-lensing effects; the only exception is, which, at fixed A_{s}e^{-2τ}, affects the > 800 temperature power spectrum solely through the associated change in A_{s} and the impact of that on the lensing potential power spectrum. We also ask, "what is it about the power spectrum at < 800 that leads to somewhat different best-fit parameters than come from the full range?" We find that if we discard the data at < 30, where there is a roughly 2σ downward fluctuation in power relative to the model that best fits the full range, the < 800 best-fit parameters shift significantly towards the < 2500 best-fit parameters. In contrast, including < 30, this previously noted "low-deficit" drives n_{s} up and impacts parameters correlated with n_{s}, such as ω_{m} and H_{0}. As expected, the < 30 data have a much greater impact on the < 800 best fit than on the < 2500 best fit. So although the shifts are not very significant, we find that they can be understood through the combined effects of an oscillatory-like set of high-residuals and the deficit in low-power, excursions consistent with sample variance that happen to map onto changes in cosmological parameters. Finally, we examine agreement between PlanckTT data and two other CMB data sets, namely the Planck lensing reconstruction and the TT power spectrum measured by the South Pole Telescope, again finding a lack of convincing evidence of any significant deviations in parameters, suggesting that current CMB data sets give an internally consistent picture of the ΛCDM model.

### Details

Original language | English |
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Article number | A95 |

Number of pages | 27 |

Journal | Astronomy and Astrophysics |

Volume | 607 |

Publication status | Published - 1 Nov 2017 |

MoE publication type | A1 Journal article-refereed |

- Cosmic background radiation, Cosmological parameters, Cosmology: observations, Cosmology: theory

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