2012ApJ...756...10L

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 ∼1 pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0^ + 2.8^_- 1.4_x10³ M_☉, 0.6 pc scale central molecular clump, and may directly channel the molecular gas to the warm (∼50 K) molecular gas immediately surrounding the centrally embedded OB stars. The NH₃ spectra suggest a medium turbulence line width of FWHM ≲ 2 km/s in the central molecular clump, implying a ≳ 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.