Neutral hydrogen structures trace dust polarization angle: Implications for cosmic microwave background foregrounds

TL;DR

This study demonstrates that neutral hydrogen structures are closely aligned with magnetic fields and can serve as an independent tracer for dust polarization angles, aiding in CMB foreground removal.

Contribution

It reveals a strong correlation between HI structures and magnetic field orientation, providing a new method to constrain dust polarization angles for CMB studies.

Findings

HI structures correlate with magnetic field orientation.

HI data can independently constrain dust polarization angles.

Strong cross-correlations with dust and starlight polarization.

Abstract

Using high-resolution data from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) survey, we show that linear structure in Galactic neutral hydrogen (HI) correlates with the magnetic field orientation implied by Planck 353 GHz polarized dust emission. The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. At high Galactic latitudes, where the Planck data are noise-dominated, the HI data provide an independent constraint on the Galactic magnetic field orientation, and hence the local dust polarization angle. We detect strong cross-correlations between template maps constructed from estimates of dust intensity combined with either HI-derived angles, starlight polarization angles, or Planck 353 GHz angles. The HI data thus provide a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination.