2016MNRAS.456.2681Q

We present Submillimeter Array observations of the HCN (3-2) and HCO+ (3-2) molecular lines towards the W3(H2O) and W3(OH) star-forming complexes. Infall and outflow motions in the W3(H2O) 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 on to the W3(H2O) dust core. The measured large mass accretion rate, 2.3x10^–3 M_☉/yr, together with the small free-fall time-scale, 5x10³ yr, suggest W3(H2O) 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/Infrared Array Camera (IRAC) images support that the W3(OH) HII region is expanding and interacting with the ambient gas, with the shocked neutral gas being expanding with an expansion time-scale of 6.4x10³ yr. The observations suggest different kinematical time-scales and dynamical states for the W3(H2O) and W3(OH).