ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic
  Cloud
  We present high-resolution (sub-parsec) observations of a giant molecular
cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band
6 observations trace the bulk of the molecular gas in $^{12}$CO(2-1) and high
column density regions in $^{13}$CO(2-1). Our target is a quiescent cloud (PGCC
G282.98-32.40, which we refer to as the "Planck cold cloud" or PCC) in the
southern outskirts of the galaxy where star-formation activity is very low and
largely confined to one location. We decompose the cloud into structures using
a dendrogram and apply an identical analysis to matched-resolution cubes of the
30 Doradus molecular cloud (located near intense star formation) for
comparison. Structures in the PCC exhibit roughly 10 times lower surface
density and 5 times lower velocity dispersion than comparably sized structures
in 30 Dor, underscoring the non-universality of molecular cloud properties. In
both clouds, structures with relatively higher surface density lie closer to
simple virial equilibrium, whereas lower surface density structures tend to
exhibit super-virial line widths. In the PCC, relatively high line widths are
found in the vicinity of an infrared source whose properties are consistent
with a luminous young stellar object. More generally, we find that the smallest
resolved structures ("leaves") of the dendrogram span close to the full range
of line widths observed across all scales. As a result, while the bulk of the
kinetic energy is found on the largest scales, the small-scale energetics tend
to be dominated by only a few structures, leading to substantial scatter in
observed size-linewidth relationships.
