VLA observations of ammonia in high-mass star formation regions

Abstract

We report systematic mapping observations of the NH${}_3$ (1,1) and (2,2) inversion lines towards 62 high-mass star-forming regions using VLA in its D and DnC array configurations. The VLA images cover a spatial dynamic range from 40$"$ to 3$"$, allowing us to trace gas kinematics from $\sim$1 pc scales to $\lesssim$0.1 pc scales. Based on the NH${}_3$ morphology and the infrared nebulosity on 1\,pc scales, we categorize three sub-classes in the sample: filaments, hot cores, and NH${}_3$ dispersed sources. The ubiquitous gas filaments found on 1 pc scales have a typical width of $\sim$0.1\,pc and often contain regularly spaced fragments along the major axis. The spacing of the fragments and the column densities are consistent with the turbulent supported fragmentation of cylinders. Several sources show multiple filaments that converge toward a center, where the velocity field in the filaments is consistent with gas flows. We derive rotational temperature maps for the entire sample. For the three hot core sources, we find a projected radial temperature distribution that is best fitted by power-law indices from $-$0.18 to $-$0.35. We identify 174 velocity-coherent $\sim$0.1 pc scale dense cores from the entire sample. The mean physical properties for these cores are 1.1 km\,s${}^{-1}$ in intrinsic linewidth, 18 K in NH${}_3$ rotational temperature, 2.3$\times$10${}^{15}$ cm${}^{-2}$ in NH${}_3$ gas column density, and 67 $M_{\odot }$ in molecular mass. The dense cores identified from the filamentary sources are closer to be virialized. Dense cores in the other two categories of sources appear to be dynamically unstable.

40 pages, 8 figues, 6 tables, ApJ accepted

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