Planck 2015 results XI. CMB power spectra, likelihoods, and robustness of parameters
Metadata
Show full item recordAuthor
Battaner López, EduardoEditorial
EDP Sciences
Materia
Cosmic background radiation Cosmological parameters Cosmology: observations Methods: data analysis Methods: statistical
Date
2016Referencia bibliográfica
Aghanim, N., Arnaud, M., Ashdown, M., Aumont, J., Baccigalupi, C., Banday, A. J., ... & Benabed, K. (2016). Planck 2015 results-XI. CMB power spectra, likelihoods, and robustness of parameters. Astronomy & Astrophysics, 594, A11. [DOI: 10.1051/0004-6361/201526926]
Sponsorship
Planck (http://www.esa.int/Planck) is a project of the European Space Agency (ESA) with instruments provided by two scientific consortia funded by ESA member states and led by Principal Investigators from France and Italy, telescope reflectors provided through a collaboration between ESA and a scientific consortium led and funded by Denmark, and additional contributions from NASA (USA).Abstract
This paper presents the Planck 2015 likelihoods, statistical descriptions of the 2-point correlation functions of the cosmic microwave background
(CMB) temperature and polarization fluctuations that account for relevant uncertainties, both instrumental and astrophysical in nature. They
are based on the same hybrid approach used for the previous release, i.e., a pixel-based likelihood at low multipoles (` < 30) and a Gaussian
approximation to the distribution of cross-power spectra at higher multipoles. The main improvements are the use of more and better processed data
and of Planck polarization information, along with more detailed models of foregrounds and instrumental uncertainties. The increased redundancy
brought by more than doubling the amount of data analysed enables further consistency checks and enhanced immunity to systematic effects. It also
improves the constraining power of Planck, in particular with regard to small-scale foreground properties. Progress in the modelling of foreground
emission enables the retention of a larger fraction of the sky to determine the properties of the CMB, which also contributes to the enhanced
precision of the spectra. Improvements in data processing and instrumental modelling further reduce uncertainties. Extensive tests establish the
robustness and accuracy of the likelihood results, from temperature alone, from polarization alone, and from their combination. For temperature,
we also perform a full likelihood analysis of realistic end-to-end simulations of the instrumental response to the sky, which were fed into the actual
data processing pipeline; this does not reveal biases from residual low-level instrumental systematics. Even with the increase in precision and
robustness, the ΛCDM cosmological model continues to offer a very good fit to the Planck data. The slope of the primordial scalar fluctuations,
ns
, is confirmed smaller than unity at more than 5σ from Planck alone. We further validate the robustness of the likelihood results against specific
extensions to the baseline cosmology, which are particularly sensitive to data at high multipoles. For instance, the effective number of neutrino
species remains compatible with the canonical value of 3.046. For this first detailed analysis of Planck polarization spectra, we concentrate at high
multipoles on the E modes, leaving the analysis of the weaker B modes to future work. At low multipoles we use temperature maps at all Planck
frequencies along with a subset of polarization data. These data take advantage of Planck’s wide frequency coverage to improve the separation
of CMB and foreground emission. Within the baseline ΛCDM cosmology this requires τ = 0.078 ± 0.019 for the reionization optical depth,
which is significantly lower than estimates without the use of high-frequency data for explicit monitoring of dust emission. At high multipoles we
detect residual systematic errors in E polarization, typically at the µK
2
level; we therefore choose to retain temperature information alone for high
multipoles as the recommended baseline, in particular for testing non-minimal models. Nevertheless, the high-multipole polarization spectra from
Planck are already good enough to enable a separate high-precision determination of the parameters of the ΛCDM model, showing consistency
with those established independently from temperature information alone.