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 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 ) .