The Kinetic Sunyaev-Zel'dovich effect of the Milky Way Halo

TL;DR

This paper models the kinetic Sunyaev-Zel'dovich effect caused by ionized gas in the Milky Way halo on the CMB, finding it detectable but below cosmic variance noise, with potential for future observational constraints.

Contribution

It provides theoretical models of the halo kSZ effect from various gas components and assesses their detectability with current data.

Findings

Halo kSZ effect is above Planck sensitivity across scales.

Halo contribution is below cosmic variance noise.

No significant cross-correlation detected with existing data.

Abstract

We calculate the expected imprint of the ionized gas in the Milky-Way halo on the Cosmic Microwave Background (CMB) through the kinetic Sunyaev-Zel'dovich (kSZ) effect. Unlike other Galactic foregrounds, the halo kSZ signature covers the full sky, generates anisotropies on large angular scales, is not accompanied by spectral distortions, and could therefore be confused with primordial CMB anisotropies. We construct theoretical models for various halo components, including smooth diffuse gas, filaments of cold inflowing gas and high velocity clouds. We find that the kSZ effect for all components is above the sensitivity of the Planck satellite, over a range of angular scales. However, the typical halo contribution is well below the cosmic variance noise in the primordial CMB power spectrum. High velocity clouds could dominate the halo contribution and better observational data is required to mask them out. We derive expected kSZ maps based on existing data from tracers of the halo gas distribution, such as 21cm maps of neutral hydrogen and H_alpha maps of recombining gas. The cross-correlation of these maps with the WMAP5 data does not yield any statistically significant signal.