FRAGMENTATION AND OB STAR FORMATION IN HIGH-MASS MOLECULAR HUB-FILAMENT SYSTEMS

Filamentary structures are ubiquitously seen in the interstellar medium. The concentrated molecular mass in the filaments allows fragmentation to occur in a shorter timescale than the timescale of the global collapse. Such hierarchical fragmentation may further assist the dissipation of excessive angular momentum. It is crucial to resolve the morphology and the internal velocity structures of the molecular filaments observationally. We perform 0 ''.5-2 ''.5 angular resolution interferometric observations toward the nearly face-on OB cluster-forming region G33.92+0.11. Observations of various spectral lines, as well as the millimeter dust continuum emission, consistently trace several similar to 1 pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0(-1.4)(+2.8)x10(3) M-circle dot, 0.6 pc scale central molecular clump, and may directly channel the molecular gas to the warm (similar to 50 K) molecular gas immediately surrounding the centrally embedded OB stars. The NH3 spectra suggest a medium turbulence line width of FWHM less than or similar to 2 km s(-1) in the central molecular clump, implying a greater than or similar to 10 times larger molecular mass than the virial mass. Feedbacks from shocks and the centrally embedded OB stars and localized (proto) stellar clusters likely play a key role in the heating of molecular gas and could lead to the observed chemical stratification. Although (proto) stellar feedbacks are already present, G33.92+0.11 chemically appears to be at an early evolutionary stage given by the low abundance limit of SO2 observed in this region.