We examine the consistency of the 9 yr WMAP data and the first-release Planck data .
We specifically compare sky maps , power spectra , and the inferred \Lambda cold dark matter ( \Lambda CDM ) cosmological parameters .
Residual dipoles are seen in the WMAP and Planck sky map differences , but their amplitudes are consistent within the quoted uncertainties , and they are not large enough to explain the widely noted differences in angular power spectra at higher l .
We remove the residual dipoles and use templates to remove residual galactic foregrounds ; after doing so , 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 to find the minimum-variance difference between the WMAP and Planck sky maps ; again we find features that plausibly originate in the Planck data .
Lacking access to the Planck time-ordered data we can not further assess these features .
We examine \Lambda CDM model fits to the angular power spectra and conclude that the \sim 2.5 % difference in the spectra at multipoles greater than l \sim 100 are significant at the 3–5 \sigma level , depending on how beam uncertainties are handled in the data .
We revisit the analysis of WMAP ’ s beam data to address the power spectrum differences and conclude that previously derived uncertainties are robust and can not explain the power spectrum differences .
In fact , any remaining WMAP errors are most likely to exacerbate the difference .
Finally , we examine the consistency of the \Lambda CDM 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 .
We find that , while individual parameter values agree within the uncertainties , the six parameters taken together are discrepant at the \sim 6 \sigma level , with \chi ^ { 2 } = 56 for 6 degrees of freedom ( probability to exceed , PTE = 3 \times 10 ^ { -10 } ) .
The nature of this discrepancy is explored : of the six parameters , \chi ^ { 2 } is best improved by marginalizing over \Omega _ { c } h ^ { 2 } , giving \chi ^ { 2 } = 5.2 for 5 degrees of freedom .
As an exercise , 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 } .