# Polarization reversal of scattered thermal dust emission in protoplanetary disks at (sub-)mm wavelengths

## TL;DR

This paper reveals that polarization patterns in protoplanetary disks can reverse by 90°, which depends on wavelength and grain size, offering new ways to study dust properties and disk orientation.

## Contribution

It demonstrates that polarization reversal due to self-scattering can mimic magnetic field signatures, providing a novel diagnostic for dust and disk characteristics.

## Key findings

- Polarization vectors can flip by 90° depending on wavelength and grain size.
- Reversal of polarization pattern can mimic magnetic field signatures.
- Polarization reversal offers constraints on dust properties and disk inclination.

## Abstract

The investigation of polarized light of protoplanetary disks is key for constraining the dust properties, disk morphology and embedded magnetic fields. However, different polarization mechanisms and the diversity of dust grain shapes and compositions lead to ambiguities in the polarization pattern. The so-called "self-scattering" of thermal, re-emitted radiation in the infrared and mm/submm is discussed as a major polarization mechanism. If the net flux of the radiation field is in radial direction, it is commonly assumed that the polarization pattern produced by scattering in a protoplanetary disk shows concentric rings for disks seen in face-on orientation. We show that a flip of $90^\circ$ of the polarization vectors may occur and mimic the typical pattern of dichroic emission of dust grains aligned by a toroidal magnetic field in disks seen close to face-on. Furthermore, this effect of polarization reversal is a fast changing function of wavelength and grain size, and thus a powerful tool to constrain grain composition and size distribution present in protoplanetary disks. In addition, the effect may also provide unique constraints for the disk inclination, especially if the disk is seen close to face-on.