# An Examination of Galactic Polarization with Application to the Planck TB Correlation

## TL;DR

This study investigates the origin of the TB correlation in Planck 353 GHz dust polarization maps, suggesting it arises from large-scale Galactic dust polarization properties rather than systematic errors.

## Contribution

It demonstrates that large-scale polarization angle structures in Galactic dust can produce the observed TB correlation, advancing understanding of dust polarization.

## Key findings

- Large-scale polarization angle structures can generate positive TB correlation.
- The TB correlation is robust against variations in dust emission models.
- The observed TB correlation likely reflects Galactic dust polarization properties.

## Abstract

Angular power spectra computed from Planck HFI 353 GHz intensity and polarization maps produce a TB correlation that can be approximated by a power law. Whether the observed TB correlation is an induced systematic feature or a physical property of Galactic dust emission is of interest both for cosmological and Galactic studies. We investigate the large angular scale E- and B-mode morphology of microwave polarized thermal dust emission, and relate it to physical quantities of polarization angle and polarization fraction. We use empirical models of polarized dust to show that dust polarization angle is a key factor in producing the TB correlation. A small sample of both simulated and observed polarization angle maps are combined with 353 GHz intensity and dust polarization fraction to produce a suite of maps from which we compute TB and EB. Model realizations that produce a positive TB correlation are common and can result from large-scale (>5 degree) structure in the polarization angle. The TB correlation appears robust to introduction of individual intensity, polarization angle and polarization fraction model components that are independent of the 353 GHz observations. We conclude that the observed TB correlation is likely the result of large-scale Galactic dust polarization properties.