Resolving the Polarized Dust Emission of the Disk around the Massive Star Powering the HH 80-81 Radio Jet

GIRART, J.M.; YANG, H.; ANEZ-LÓPEZ, N.; CURIEL, S.; GREGORIO-MONSALVO, I. DE; MARTI, J.; RAO, R.; FERNÁNDEZ-LÓPEZ, M.; ESTALELLA, R.; BUSQUET, G.; GALVAN-MADRID, R.; JIMÉNEZ-SERRA, I.; OSORIO, M.; RODRIGUEZ, L.F.; LI, Z.-Y.; ANGLADA, G.; CARRASCO-GONZÁLEZ, C.; GÓMEZ, J.F.; KRASNOPOLSKY, R.; PADOVANI, M.; TORRELLES, J.M.

Astrophysical Journal Letters

Institute of Physics Publishing

Año: 2018 vol. 856

2041-8205

Here we present deep (16 μJy beam-1), very high (40 mas) angular resolution 1.14 mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protostar driving the HH 80-81 radio jet. The observations clearly resolve the disk oriented perpendicularly to the radio jet, with a radius of ≃0.″171 (∼291 au at 1.7 kpc distance). The continuum brightness temperature, the intensity profile, and the polarization properties clearly indicate that the disk is optically thick for a radius of R ≲ 170 au. The linear polarization of the dust emission is detected almost all along the disk, and its properties suggest that dust polarization is produced mainly by self-scattering. However, the polarization pattern presents a clear differentiation between the inner (optically thick) part of the disk and the outer (optically thin) region of the disk, with a sharp transition that occurs at a radius of ∼0.″1 (∼170 au). The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 μm. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk. This pattern is broadly consistent with the self-scattering of a radiation field that is beamed radially outward, as expected in the optically thin outer region, although contribution from non-spherical grains aligned with respect to the radiative flux cannot be excluded.