Structure of W3(OH) from Very High Spectral Resolution Observations of 5 Centimeter OH Masers

TL;DR

This study models the structure of W3(OH) using high spectral resolution observations of 5 cm OH masers, revealing magnetic field regions, maser brightness evolution, and detailed velocity and spatial structures.

Contribution

It provides a detailed model of W3(OH) based on EVN observations, highlighting magnetic fields, maser dynamics, and spatial structures at very high spectral resolution.

Findings

6.0 GHz masers are brightening over time.

Magnetic fields are oriented toward the observer in specific regions.

Masers trace a rotating torus and show complex velocity gradients.

Abstract

Recent studies of methanol and ground-state OH masers at very high spectral resolution have shed new light on small-scale maser processes. The nearby source W3(OH), which contains numerous bright masers in several different transitions, provides an excellent laboratory for high spectral resolution techniques. We present a model of W3(OH) based on EVN observations of the rotationally-excited 6030 and 6035 MHz OH masers taken at 0.024 km/s spectral resolution. The 6.0 GHz masers are becoming brighter with time and show evidence for tangential proper motions. We confirm the existence of a region of magnetic field oriented toward the observer to the southeast and find another such region to the northeast in W3(OH), near the champagne flow. The 6.0 GHz masers trace the inner edge of a counterclockwise rotating torus feature. Masers at 6030 MHz are usually a factor of a few weaker than at 6035 MHz but trace the same material. Velocity gradients of nearby Zeeman components are much more closely correlated than in the ground state, likely due to the smaller spatial separation between Zeeman components. Hydroxyl maser peaks at very long baseline interferometric resolution appear to have structure on scales both smaller than that resolvable as well as on larger scales.