Are CMB derived cosmological parameters affected by foregrounds associated to nearby galaxies?

TL;DR

This study investigates whether foregrounds from nearby spiral galaxies influence cosmological parameters derived from Planck CMB maps, finding that while small-sky analyses are affected, full-sky estimates remain robust.

Contribution

It introduces a model for a new extragalactic foreground linked to nearby spiral galaxies and assesses its impact on cosmological parameter estimation.

Findings

Full-sky parameter estimates are unaffected by the foreground.

Foreground modeling shows a 40-50% correlation with local parameter variations.

Masking foregrounds reduces uncertainties but does not bias full-sky results.

Abstract

We perform cosmological parameters estimation on Planck Cosmic Microwave Background (CMB) maps masking the recently discovered foreground related to nearby spiral galaxies. In addition, we also analyse the association between these foreground regions and recent claims of cosmological causal horizons in localized CMB parameter estimates. Our analysis shows consistent cosmological parameter values regardless of the masking approach, though reduced sky areas introduce larger uncertainties. By modelling the new extragalactic foreground, we identify a resemblance with local parameter variation maps with a statistical significance at the 3 sigma level, suggesting that a simplified foreground model partially accounts, (40-50)% correlation with 15% uncertainty, for the observed causal horizons. These findings add new evidence to the existence of the new foreground associated with large spiral galaxies and show that estimates of cosmological parameters on smaller patches on the sky can be largely affected by these foregrounds, but that the parameters taken over the full sky are unaltered.