On the impact of large angle CMB polarization data on cosmological parameters

TL;DR

This study assesses how large-angle CMB polarization data from WMAP and Planck influence cosmological parameter estimates, highlighting the importance of dust removal methods and their impact on parameters like the Hubble constant.

Contribution

It provides a detailed analysis of the effects of polarized dust mitigation techniques on cosmological parameters, especially the optical depth and Hubble constant, using independent polarization likelihoods.

Findings

Consistent dust removal with Planck 353 GHz data aligns WMAP and Planck polarization results.

Dust cleaning methods significantly affect the estimated optical depth and Hubble constant.

The low $ au$ value reduces the tension between CMB and direct $H_0$ measurements.

Abstract

(abridged) We study the impact of the large-angle CMB polarization datasets publicly released by the WMAP and Planck satellites on the estimation of cosmological parameters of the $\Lambda$CDM model. To complement large-angle polarization, we consider the high-resolution CMB datasets from either WMAP or Planck, as well as CMB lensing as traced by Planck. In the case of WMAP, we compute the large-angle polarization likelihood starting over from low-resolution frequency maps and their covariance matrices, and perform our own foreground mitigation technique, which includes as a possible alternative Planck 353 GHz data to trace polarized dust. We find that the latter choice induces a downward shift in the optical depth $\tau$, of order ~$2\sigma$, robust to the choice of the complementary high-l dataset. When the Planck 353 GHz is consistently used to minimize polarized dust emission, WMAP and Planck 70 GHz large-angle polarization data are in remarkable agreement: by combining them we find $\tau = 0.066 ^{+0.012}_{-0.013}$, again very stable against the particular choice for high-$\ell$ data. We find that the amplitude of primordial fluctuations $A_s$, notoriously degenerate with $\tau$, is the parameter second most affected by the assumptions on polarized dust removal, but the other parameters are also affected, typically between $0.5$ and $1\sigma$. In particular, cleaning dust with \planck's 353 GHz data imposes a $1\sigma$ downward shift in the value of the Hubble constant $H_0$, significantly contributing to the tension reported between CMB based and direct measurements of $H_0$. On the other hand, we find that the appearance of the so-called low $\ell$ anomaly, a well-known tension between the high- and low-resolution CMB anisotropy amplitude, is not significantly affected by the details of large-angle polarization, or by the particular high-$\ell$ dataset employed.