Comparing Planck and WMAP: Maps, Spectra, and Parameters

Abstract

We examine the consistency of WMAP9 and Planck data. We compare sky maps, power spectra, and inferred LCDM cosmological parameters. Residual dipoles are seen in the WMAP and Planck sky map differences, but are consistent within the uncertainties and are not large enough to explain the widely-noted differences in angular power spectra at higher l. After removing residual dipoles and galactic foregrounds, the residual difference maps exhibit a quadrupole and other large-scale systematic structure. We identify this structure as possibly originating from Planck's beam sidelobe pick-up, but note that it appears to have insignificant cosmological impact. We develop an extension of the internal linear combination technique and find features that plausibly originate in the Planck data. We examine LCDM model fits to the angular power spectra and conclude that the ~2.5% difference in the spectra at multipoles greater than l~100 are significant at the 3-5 sigma level. We revisit the analysis of WMAP's beam data and conclude that previously-derived uncertainties are robust and cannot explain the power spectrum differences. Finally, we examine the consistency of the LCDM parameters inferred from each data set taking into account the fact that both experiments observe the same sky, but cover different multipole ranges, apply different sky masks, and have different noise. While individual parameter values agree within the uncertainties, the 6 parameters taken together are discrepant at the ~6 sigma level, with chi2=56 for 6 dof (PTE = 3e-10). Of the 6 parameters, chi2 is best improved by marginalizing over Omega_c h^2, giving chi2=5.2 for 5 degrees of freedom. We find that perturbing the WMAP window function by its dominant beam error profile has little effect on Omega_c h^2, while perturbing the Planck window function by its corresponding error profile has a much greater effect on Omega_c h^2.