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