Fragmentation and OB Star Formation in High-Mass Molecular Hub-Filament System

TL;DR

This study investigates the hierarchical fragmentation and gas dynamics in a high-mass molecular hub-filament system G33.92+0.11, revealing how filamentary structures channel gas to form OB stars and influence chemical and physical conditions.

Contribution

It provides high-resolution interferometric observations of the G33.92+0.11 region, elucidating the morphology, velocity structure, and early evolutionary stage of high-mass star formation within a hub-filament system.

Findings

Identification of ~1 pc scale molecular arms channeling gas to the central clump.

Detection of a central molecular clump with mass ~10^3 M_sun and size 0.6 pc.

Evidence of early evolutionary stage with low SO2 abundance.

Abstract

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 $\sim$1 pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0$^{{\scriptsize{+2.8}}}_{{-\scriptsize{1.4}}}\cdot10^{3}$\,$M_{\odot}$, 0.6 pc scale central molecular clump, and may directly channel the molecular gas to the warm ($\sim$50 K) molecular gas immediately surrounding the centrally embedded OB stars. The NH$_{3}$ spectra suggest a medium turbulence line width of FWHM$\lesssim$2\,km\,s$^{-1}$ in the central molecular clump, implying a $\gtrsim$10 times larger molecular mass than the virial mass. Feedbacks from shocks and the centrally embedded OB stars and localized (proto)stellar clusters, likely play a key role in the heating of molecular gas and could lead to the observed chemical stratification. Although (proto)stellar feedbacks are already present, G33.92+0.11 chemically appears to be at an early evolutionary stage given by the low abundance limit of SO$_{2}$ observed in this region.