Foreground contribution to the inferred cosmological parameters from Planck

Abstract

Previous analyses of cosmic microwave background (CMB) measurements [T. Wibig and A. W. Wolfendale, Mon. Not. R. Astron. Soc. 360 (2005) 236, arXiv:astro-ph/0409397; Mon. Not. R. Astron. Soc. 448 (2015) 1030, arXiv:1507.0677.] have revealed contamination by areas of high cosmic ray activity in the Milky Way. Here, we update studies, looking at the most recent Planck release of residual maps. We search for possible effects of foreground contamination in the reconstruction of the [Formula: see text]CDM cosmological parameters. We focus on the Hubble parameter [Formula: see text] and the optical depth to reionization [Formula: see text], both of which exhibit discrepancies between CMB-inferred values and low-redshift measurements (“the delta [Formula: see text] problem”). Using the publicly available “component separated” Planck temperature maps, we single out three distinct regions: the “loops”, “chimneys” and “low CR” regions, which disproportionately contributed to CR contamination of WMAP data. We find that two of the four maps are strongly affected by removal of anomalously high or low CR activity regions. However, the Commander method, used to produce the angular power spectrum at low ([Formula: see text]) multipoles in cosmological analyses, appears robust under these changes. Finally, we use the inferred Hubble parameter [Formula: see text] as a proxy to look for general directional dependence of the CMB power spectrum, finding a small but robust dependence on the Galactic longitude. Although there is some evidence for a continuing CR contamination, it is insufficient to provide an answer to the delta [Formula: see text] problem, or to the optical depth problem, though dependence of the derived [Formula: see text] on direction seems significant. The geometrical pattern — striations along constant longitudes — suggests CR contamination as distinct from a truly cosmological effect.