Assessing Consistency Between WMAP 9-year and Planck 2015 Temperature Power Spectra

TL;DR

This study compares WMAP 9-year and Planck 2015 CMB temperature power spectra, finding they are consistent within uncertainties, thus confirming the reliability of both datasets for cosmological analysis.

Contribution

The paper provides a detailed comparison of WMAP9 and Planck 2015 spectra, demonstrating their consistency and assessing the impact of analysis choices on this comparison.

Findings

Spectra are consistent within 1 sigma across multipoles 30 to 1200.

Changing analysis parameters shifts results by less than 0.66 sigma.

Cosmological differences are due to high multipoles, not measurement discrepancies.

Abstract

We perform a comparison of WMAP 9-year (WMAP9) and Planck 2015 cosmic microwave background (CMB) temperature power spectra across multipoles $30\leq\ell\leq1200$. We generate simulations to estimate the correlation between the two datasets due to cosmic variance from observing the same sky. We find that their spectra are consistent within $1\sigma$. While we do not implement the optimal "$C^{-1}$" estimator on WMAP maps as in the WMAP9 analysis, we demonstrate that the change of pixel weighting only shifts our results at most at the $0.66\sigma$ level. We also show that changing the fiducial power spectrum for simulations only impacts the comparison at around $0.1\sigma$ level. We exclude $\ell<30$ both because WMAP9 data were included in the Planck 2015 $\ell<30$ analysis, and because the cosmic variance uncertainty on these scales is large enough that any remaining systematic difference between the experiments is extremely unlikely to affect cosmological constraints. The consistency shown in our analysis provides high confidence in both the WMAP9 temperature power spectrum and the overlapping multipole region of Planck 2015's, virtually independent of any assumed cosmological model. Our results indicate that cosmological model differences between Planck and WMAP do not arise from measurement differences, but from the high multipoles not measured by WMAP.