SMA observations of the W3(OH) complex: Dynamical differentiation between W3(H$_2$O) and W3(OH)

TL;DR

This study uses SMA observations of molecular lines to analyze the dynamical states of W3(H$_2$O) and W3(OH), revealing infall in W3(H$_2$O) and expansion in W3(OH), indicating different evolutionary stages.

Contribution

It provides detailed kinematic analysis of W3(H$_2$O) and W3(OH), highlighting their distinct dynamical processes and evolutionary stages through molecular line observations.

Findings

W3(H$_2$O) shows infall with high mass accretion rate.

W3(OH) exhibits expanding HII region with a timescale of 6.4×10^3 years.

Different dynamical states suggest varied evolutionary stages.

Abstract

We present Submillimeter Array (SMA) observations of the HCN\,(3--2) and HCO$^+$\,(3--2) molecular lines toward the W3(H$_2$O) and W3(OH) star-forming complexes. Infall and outflow motions in the W3(H$_2$O) have been characterized by observing HCN and HCO$^+$ transitions. High-velocity blue/red-shifted emission, tracing the outflow, show multiple knots, which might originate in episodic and precessing outflows. `Blue-peaked' line profiles indicate that gas is infalling onto the W3(H$_2$O) dust core. The measured large mass accretion rate, 2.3$\times$10$^{-3}$~M$_{\odot}$~yr$^{-1}$, together with the small free-fall time scale, 5$\times$10$^{3}$~yr, suggest W3(H$_2$O) is in an early evolutionary stage of the process of formation of high-mass stars. For the W3(OH), a two-layer model fit to the HCN and HCO$^+$ spectral lines and Spizter/IRAC images support that the W3(OH) H{\sc ii} region is expanding and interacting with the ambient gas, with the shocked neutral gas being expanding with an expansion timescale of 6.4$\times$10$^{3}$~yr. The observations suggest different kinematical timescales and dynamical states for the W3(H$_2$O) and W3(OH).