Protostellar Outflows at the EarliesT Stages (POETS). III. H2O masers tracing disk-winds and jets near luminous YSOs

TL;DR

This study uses VLBI observations of water masers to investigate the kinematics of disk-winds and jets near luminous young stellar objects, revealing structures consistent with protostellar outflows and disk-winds at scales of 10-100 au.

Contribution

It provides new high-resolution evidence of disk-wind and jet structures in a significant sample of luminous YSOs, linking maser kinematics to outflow mechanisms.

Findings

Water masers trace jet and disk-wind structures near YSOs.

Disk-wind orientations are perpendicular to jets and aligned with thermal emission gradients.

Maser proper motions suggest flow speeds of 10-20 km/s at large angles to the disk midplane.

Abstract

The goal of the Protostellar Outflows at the EarliesT Stages (POETS) survey is to image the disk-outflow interface on scales of 10-100 au in a statistically significant sample (36) of luminous young stellar objects (YSO), targeting both the molecular and ionized components of the outflows. The outflow kinematics is studied at milliarcsecond scales through VLBI observations of the 22 GHz water masers. We employed the JVLA at 6, 13, and 22 GHz in the A- and B-Array configurations to determine the spatial structure and the spectral index of the radio continuum emission. In about half of the targets, the water masers observed at separation <= 1000 au from the YSOs trace either or both of these kinematic structures: 1) a spatially elongated distribution oriented at close angle with the direction of collimation of the maser proper motions (PM), and 2) a linear LSR velocity (Vlsr) gradient across the YSO position. The kinematic structure (1) is readily interpreted in terms of a protostellar jet, as confirmed in some targets via the comparison with independent observations of the YSO jets, in thermal (continuum and line) emissions, reported in the literature. The kinematic structure (2) is interpreted in terms of a disk-wind (DW) seen almost edge-on on the basis of several pieces of evidence: first, it is invariably directed perpendicular to the YSO jet; second, it agrees in orientation and polarity with the Vlsr gradient in thermal emissions (when reported in the literature) identifying the YSO disk at scales of <= 1000~au; third, the PMs of the masers delineating the Vlsr gradients hint at flow motions at a speed of 10-20 km/s directed at large angles with the disk midplane. In the remaining targets, the maser PMs are not collimated but rather tend to align along two almost perpendicular directions, and could originate in DW-jet systems slightly inclined (<= 30 deg) with respect to edge-on.