SMA observations of the W3(OH) complex: Dynamical differentiation between W3(H2O) and W3(OH)

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, 2.3 × 10^-3 M_⊙ yr^-1, together with the small free-fall time-scale, 5 × 10³ 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) H II region is expanding and interacting with the ambient gas, with the shocked neutral gas being expanding with an expansion time-scale of 6.4 × 10³ yr. The observations suggest different kinematical time-scales and dynamical states for the W3(H₂O) and W3(OH).