ALMA observations of NGC 6334S. II. Subsonic and Transonic Narrow Filaments in a High-mass Star Formation Cloud

TL;DR

This study uses ALMA observations to analyze narrow filaments in the high-mass star formation cloud NGC 6334S, revealing their physical properties, low turbulence support, and implications for star formation environments.

Contribution

It provides high-resolution measurements of filament widths and kinematics, showing they are narrower and less turbulent than previously thought, with implications for star formation theories.

Findings

Filament widths are ~0.04 pc, narrower than the 0.1 pc universal width.

Gas filaments are mainly supported by thermal motions with subsonic and transonic turbulence.

Embedded objects often have narrower velocity dispersions, indicating turbulent dissipation.

Abstract

We present a study of narrow filaments toward a massive infrared dark cloud, NGC 6334S, using the Atacama Large Millimeter/submillimeter Array (ALMA). Thirteen gas filaments are identified using the H$^{13}$CO$^{+}$ line, while a single continuum filament is revealed by the continuum emission. The filaments present a compact radial distribution with a median filament width of $\sim$0.04 pc narrower than the previously proposed `quasi-universal' 0.1~pc filament width. The higher spatial resolution observations and higher-density gas tracer tend to identify even narrower and lower mass filaments. The filament widths are roughly twice the size of embedded cores. The gas filaments are largely supported by thermal motions. The nonthermal motions are predominantly subsonic and transonic in both identified gas filaments and embedded cores, which may imply that stars are likely born in environments of low turbulence. A fraction of embedded objects show a narrower velocity dispersion compared with their corresponding natal filaments, which may indicate that the turbulent dissipation is taking place in these embedded cores. The physical properties (mass, mass per unit length, gas kinematics, and width) of gas filaments are analogous to those of narrow filaments found in low- to high-mass star-forming regions. The more evolved sources are found to be farther away from the filaments, a situation that may have resulted from the relative motions between the YSOs and their natal filaments.