Search for Alignment of Disk Orientations in Nearby Star-Forming Regions: Lupus, Taurus, Upper Scorpius, $\rho$ Ophiuchi, and Orion

TL;DR

This study investigates whether proto-planetary disks in nearby star-forming regions are aligned or randomly oriented, finding mostly random orientations but hints of alignment in the Lupus III cloud related to filament and magnetic field directions.

Contribution

It provides the first statistical analysis of disk orientations across multiple star-forming regions using ALMA and HST data, revealing mostly random orientations with potential weak alignment in Lupus III.

Findings

Disks in most regions show no significant alignment, supporting random orientation.

Weak alignment observed in Lupus III correlates with filament and magnetic field directions.

Robustness of PA measurements confirmed across different methods.

Abstract

Spatial correlations among proto-planetary disk orientations carry unique information on physics of multiple star formation processes. We select five nearby star-forming regions that comprise a number of proto-planetary disks with spatially-resolved images with ALMA and HST, and search for the mutual alignment of the disk axes. Specifically, we apply the Kuiper test to examine the statistical uniformity of the position angle (PA: the angle of the major axis of the projected disk ellipse measured counter-clockwise from the north) distribution. The disks located in the star-forming regions, except the Lupus clouds, do not show any signature of the alignment, supporting the random orientation. Rotational axes of 16 disks with spectroscopic measurement of PA in the Lupus III cloud, a sub-region of the Lupus field, however, exhibit a weak and possible departure from the random distribution at a $2\sigma$ level, and the inclination angles of the 16 disks are not uniform as well. Furthermore, the mean direction of the disk PAs in the Lupus III cloud is parallel to the direction of its filament structure, and approximately perpendicular to the magnetic field direction. We also confirm the robustness of the estimated PAs in the Lupus clouds by comparing the different observations and estimators based on three different methods including sparse modeling. The absence of the significant alignment of the disk orientation is consistent with the turbulent origin of the disk angular momentum. Further observations are required to confirm/falsify the possible disk alignment in the Lupus III cloud.