ALMA Dust Polarization Observations of Two Young Edge-on Protostellar Disks

TL;DR

This study presents ALMA observations of polarized dust emission in two young edge-on protostellar disks, revealing diverse polarization patterns likely influenced by magnetic fields, grain alignment, and scattering effects, advancing understanding of disk magnetic structures.

Contribution

First high-resolution polarization observations of two young edge-on disks, highlighting diverse polarization morphologies and potential magnetic field configurations.

Findings

Polarization fraction ~1% in both disks.

Different polarization patterns suggest complex magnetic and scattering influences.

Evidence supporting poloidal and toroidal magnetic fields in the disks.

Abstract

Polarized emission is detected in two young nearly edge-on protostellar disks in 343 GHz continuum at ~ 50 au (~ 0.12") resolution with Atacama Large Millimeter/submillimeter Array. One disk is in HH 212 (Class 0) and the other in HH 111 (early Class I) protostellar system. Polarization fraction is ~ 1%. The disk in HH 212 has a radius of ~ 60 au. The emission is mainly detected from the nearside of the disk. The polarization orientations are almost perpendicular to the disk major axis, consistent with either self-scattering or emission by grains aligned with a poloidal field around the outer edge of the disk because of optical depth effect and temperature gradient; the presence of a poloidal field would facilitate the launching of a disk wind, for which there is already tentative evidence in the same source. The disk of HH 111 VLA 1 has a larger radius of ~ 220 au and is thus more resolved. The polarization orientations are almost perpendicular to the disk major axis in the nearside, but more along the major axis in the farside, forming roughly half of an elliptical pattern there. It appears that toroidal and poloidal magnetic field may explain the polarization on the near and far side of the disk, respectively. However, it is also possible that the polarization is due to self-scattering. In addition, alignment of dust grains by radiation flux may play a role in the farside. Our observations reveal a diversity of disk polarization patterns that should be taken into account in future modeling efforts.