A cluster in the making: ALMA reveals the initial conditions for
  high-mass cluster formation
  G0.253+0.016 is a molecular clump that appears to be on the verge of forming
a high mass, Arches-like cluster. Here we present new ALMA observations of its
small-scale (~0.07 pc) 3mm dust continuum and molecular line emission. The data
reveal a complex network of emission features, the morphology of which ranges
from small, compact regions to extended, filamentary structures that are seen
in both emission and absorption. The dust column density is well traced by
molecules with higher excitation energies and critical densities, consistent
with a clump that has a denser interior. A statistical analysis supports the
idea that turbulence shapes the observed gas structure within G0.253+0.016. We
find a clear break in the turbulent power spectrum derived from the optically
thin dust continuum emission at a spatial scale of ~0.1 pc, which may
correspond to the spatial scale at which gravity has overcome the thermal
pressure. We suggest that G0.253+0.016 is on the verge of forming a cluster
from hierarchical, filamentary structures that arise from a highly turbulent
medium. Although the stellar distribution within Arches-like clusters is
compact, centrally condensed and smooth, the observed gas distribution within
G0.253+0.016 is extended, with no high-mass central concentration, and has a
complex, hierarchical structure. If this clump gives rise to a high-mass
cluster and its stars are formed from this initially hierarchical gas
structure, then the resulting cluster must evolve into a centrally condensed
structure via a dynamical process.
