CMB Isotropy Anomalies and the Local Kinetic Sunyaev-Zel'dovich Effect

TL;DR

This paper investigates whether local universe effects, specifically the Milky Way's gaseous halo via the kinetic Sunyaev-Zel'dovich effect, could explain observed anomalies in the cosmic microwave background's isotropy.

Contribution

It introduces a novel local universe mechanism involving the Milky Way's gaseous halo to account for CMB anomalies, emphasizing the potential impact of local structures.

Findings

Screening maps can significantly influence anomaly statistics

Anisotropic free electron optical depth affects CMB anisotropy

Higher-than-observed electron column densities are required for significant effects

Abstract

Several anomalies have been identified which may imply a breakdown of the statistical isotropy of the cosmic microwave background (CMB). In particular, an anomalous alignment of the quadrupole and octopole and a hemispherical power asymmetry have increased in significance as the data have improved. There have been several attempts to explain these observations which explore isotropy breaking mechanisms within the early universe, but little attention has been given to the possibility that these anomalies have their origin within the local universe. We explore such a mechanism by considering the kinetic Sunyaev-Zel'dovich effect due to a gaseous halo associated with the Milky Way. Considering several physical models of an anisotropic free electron optical depth contributed by such a halo, we find that the associated screening maps of the primordial anisotropies have the necessary orientations to affect the anomaly statistics very significantly, but only if the column density of free electrons in the halo is at least an order of magnitude higher than indicated by current observations.