Velocity and magnetic fields within 1000 AU from a massive YSO

TL;DR

This study uses high-resolution polarimetric observations of methanol masers to map the velocity and magnetic field structures within 1000 AU of a massive young stellar object, revealing complex gas dynamics and magnetic configurations.

Contribution

It provides the first detailed picture of gas dynamics and magnetic field morphology within 2000 AU of a massive YSO, combining polarimetric and velocity data at very high spatial resolution.

Findings

Magnetic field lines are smoothly changing in the outer envelope regions.

Velocity vectors mostly align with magnetic fields but show a 30-degree average misalignment.

Gas flows are collimated along the outflow axis and show inflow and outflow patterns in the disk region.

Abstract

We want to study the velocity and magnetic field morphology in the vicinity (<1000 AU) of a massive young stellar object (YSO), at very high spatial resolution (10-100 AU). We performed milli-arcsecond polarimetric observations of the strong CH3OH maser emission observed in the vicinity of an O-type YSO, in G023.01-00.41. We have combined this information with the velocity field of the CH3OH masing gas previously measured at the same angular resolution. We analyse the velocity and magnetic fields in the reference system defined by the direction of the molecular outflow and the equatorial plane of the hot molecular core at its base, as recently observed on sub-arcsecond scales. We provide a first detailed picture of the gas dynamics and magnetic field configuration within a radius of 2000 AU from a massive YSO. We have been able to reproduce the magnetic field lines for the outer regions (>600 AU) of the molecular envelope, where the magnetic field orientation shows a smooth change with the maser cloudlets position (0.2 degree/AU). Overall, the velocity field vectors well accommodate with the local, magnetic field direction, but still show an average misalignment of 30 degrees. We interpret this finding as the contribution of a turbulent velocity field of about 3.5 km/s, responsible for braking up the alignment between the velocity and magnetic field vectors. We do resolve different gas flows which develop both along the outflow axis and across the disk plane, with an average speed of 7 km/s. In the direction of the outflow axis, we establish a collimation of the gas flow, at a distance of about 1000 AU from the disk plane. In the disk region, gas appears to stream outward along the disk plane for radii greater than 500-600 AU, and inward for shorter radii.