Planck 2013 results. XV. CMB power spectra and likelihood

Articolo

Data di Pubblicazione:

2014

Abstract:

This paper presents the Planck 2013 likelihood, a complete statistical
description of the two-point correlation function of the CMB temperature
fluctuations that accounts for all known relevant uncertainties, both
instrumental and astrophysical in nature. We use this likelihood to
derive our best estimate of the CMB angular power spectrum from Planck
over three decades in multipole moment, l, covering 2 <= l
<= 2500. The main source of uncertainty at l ≲ 1500 is cosmic
variance. Uncertainties in small-scale foreground modelling and
instrumental noise dominate the error budget at higher ls. For l
< 50, our likelihood exploits all Planck frequency channels from 30
to 353 GHz, separating the cosmological CMB signal from diffuse Galactic
foregrounds through a physically motivated Bayesian component separation
technique. At l >= 50, we employ a correlated Gaussian likelihood
approximation based on a fine-grained set of angular cross-spectra
derived from multiple detector combinations between the 100, 143, and
217 GHz frequency channels, marginalising over power spectrum foreground
templates. We validate our likelihood through an extensive suite of
consistency tests, and assess the impact of residual foreground and
instrumental uncertainties on the final cosmological parameters. We find
good internal agreement among the high-l cross-spectra with
residuals below a few muK² at l ≲ 1000, in
agreement with estimated calibration uncertainties. We compare our
results with foreground-cleaned CMB maps derived from all Planck
frequencies, as well as with cross-spectra derived from the 70 GHz
Planck map, and find broad agreement in terms of spectrum residuals and
cosmological parameters. We further show that the best-fit LambdaCDM
cosmology is in excellent agreement with preliminary PlanckEE and TE
polarisation spectra. We find that the standard LambdaCDM cosmology is
well constrained by Planck from the measurements at l ≲ 1500.
One specific example is the spectral index of scalar perturbations, for
which we report a 5.4sigma deviation from scale invariance,
n_s = 1. Increasing the multipole range beyond l ~=
1500 does not increase our accuracy for the LambdaCDM parameters, but
instead allows us to study extensions beyond the standard model. We find
no indication of significant departures from the LambdaCDM framework.
Finally, we report a tension between the Planck best-fit LambdaCDM
model and the low-l spectrum in the form of a power deficit of 5-10%
at l ≲ 40, with a statistical significance of 2.5-3sigma.
Without a theoretically motivated model for this power deficit, we do
not elaborate further on its cosmological implications, but note that
this is our most puzzling finding in an otherwise remarkably consistent
data set.

Tipologia CRIS:

1.1 Articolo in rivista

Keywords:

cosmic background radiation; cosmological parameters; cosmology: observations; methods: data analysis

Elenco autori: