ALMA observations of NGC 6334S $-$ I: Forming massive stars and cluster
  in subsonic and transonic filamentary clouds
  We present Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G.
Jansky Very Large Array (JVLA) observations of the massive infrared dark cloud
NGC 6334S (also known as IRDC G350.56+0.44), located at the southwestern end of
the NGC 6334 molecular cloud complex. The H$^{13}$CO$^{+}$ and the NH$_{2}$D
lines covered by the ALMA observations at a $\sim$3$^{\prime\prime}$ angular
resolution ($\sim$0.02 pc) reveal that the spatially unresolved non-thermal
motions are predominantly subsonic and transonic, a condition analogous to that
found in low-mass star-forming molecular clouds. The observed supersonic
non-thermal velocity dispersions in massive star forming regions, often
reported in the literature, might be significantly biased by poor spatial
resolutions that broaden the observed line widths due to unresolved motions
within the telescope beam. Our 3~mm continuum image resolves 49 dense cores,
whose masses range from 0.17 to 14 $M_{\odot}$. The majority of them are
resolved with multiple velocity components. Our analyses of these gas velocity
components find an anti-correlation between the gas mass and the virial
parameter. This implies that the more massive structures tend to be more
gravitationally unstable. Finally, we find that the external pressure in the
NGC 6334S cloud is important in confining these dense structures, and may play
a role in the formation of dense cores, and subsequently, the embedded young
stars.
