THE H-II MOLECULAR CLOUD COMPLEX W3 REVISITED - IMAGING THE RADIO-CONTINUUM SOURCES USING MULTI-CONFIGURATION, MULTIFREQUENCY OBSERVATIONS WITH THE VLA

The H II/molecular cloud complex W3 has been imaged at 4.9 GHz, 14.9 G Hz and 22.5 GHz in the radio continuum and the H66 alpha radio recombi nation line with subarcsecond angular resolution using combined multip le VLA configurations. Several hypercompact continuum sources with dia meters less than or equal to 1000 AU have been detected toward IRS 4 a nd IRS 5, reminiscent of the ''Orion Radio Zoo''. They have been image d with a maximum angular resolution of 0.'' 1. From the flux densities at 1.3 cm, 2 cm and 6 cm we determine their spectral indices. The com pact and ultracompact H II regions with diameters < 20, 000 AU exhibit spectral indices alpha in the range -0.1 to < 1.5. The gradients in s pectral indices across these regions correspond to asymmetries in thei r radio continuum intensities as well as gradients in the densities of the surrounding molecular gas. This indicates gradients in the electr on density. From a direct comparison of the continuum emission of the ionized hydrogen gas with the emission of the dense molecular gas and dust continuum, we refine the analyses of the interaction of the radio components with the molecular gas. From our H66 alpha recombination l ine data we compare the radial velocities of the H II regions with tho se found for the molecular gas toward W3. We find linewidth and veloci ty gradients in the ionized gas which are indicative of expansion and turbulent flows caused by pressure gradients in the ambient neutral ga s. We propose that the observed morphologies of compact and ultracompa ct H II regions are determined by turbulent expansion of the ionized g as into highly anisotropic and clumpy molecular gas. Thus, we believe there can be no definite prediction for the morphologies observed in H II regions with current kinematic models without considering these inh omogeneities. Furthermore, we propose that the spatial and kinematic r elation of the compact, ultracompact and hypercompact radio continuum regions toward W3 is indicative of sequentially triggered star formati on caused by the pressure of the expanding H II regions and the subseq uent compression of the molecular gas.