What Produces Dust Polarization in the HH 212 Protostellar Disk at 878 μm: Dust Self-scattering or Dichroic Extinction?

We report the results of new dust polarization of a nearly edge-on disk in the HH 212 protostellar system, obtained with the Atacama Large Millimeter/submillimeter Array at similar to 0.035 '' (14 au) resolution in a continuum at lambda similar to 878 mu m. Dust polarization is detected within similar to 44 au of the central source, where a rotationally supported disk has formed. The polarized emission forms V-shaped structures opening to the east, and probably to the west, arising from the disk surfaces and arm structures further away in the east and west, which could be due to potential spiral arms excited in the outer disk. The orientations of the polarization are mainly parallel to the minor axis of the disk, with some in the western part tilting slightly away from the minor axis to form a concave shape with respect to the center. This tilting of the orientations of the polarization is expected from dust self-scattering, e.g., by 50-75 mu m grains in a young disk. The intensity and degree of the polarization both peak near the central source with a small dip at the central source and decrease toward the edges. These decreases in the intensity and degree of polarization are expected from dichroic extinction by grains aligned by poloidal fields, but may also be consistent with dust self-scattering if the grain size decreases toward the edges. It is possible that both mechanisms are needed to produce the observed dust polarization, suggesting the presence of both grain growth and poloidal fields in the disk.

Automated summary

This study presents new results on dust polarization in a nearly edge-on disk in the HH 212 protostellar system. The polarized emission forms V-shaped structures opening to the east and possibly to the west, potentially arising from spiral arms in the outer disk. The orientations of the polarization are mainly parallel to the minor axis of the disk, with some slight tilting in the western part, likely due to dust self-scattering.