ALMA Observations of the Antennae Galaxies: I. A New Window on a
  Prototypical Merger
  We present the highest spatial resolution (~0.5") CO (3-2) observations to
date of the "overlap" region in the merging Antennae galaxies (NGC 4038/39),
taken with the ALMA. We report on the discovery of a long (3 kpc), thin (aspect
ratio 30/1), filament of CO gas which breaks up into roughly ten individual
knots. Each individual knot has a low internal velocity dispersion (~10 km/s),
and the dispersion of the ensemble of knots in the filament is also low (~10
km/s). At the other extreme, we find that the individual clouds in the Super
Giant Molecular Cloud 2 region discussed by Wilson and collaborators have a
large range of internal velocity dispersions (10 to 80 km/s), and a large
dispersion amongst the ensemble (~80 km/s). We use a combination of optical and
near-IR data from HST, radio continuum observations taken with the VLA, and CO
data from ALMA to develop an evolutionary classification system which provides
a framework for studying the sequence of star cluster formation and evolution,
from diffuse SGMCs, to proto, embedded, emerging, young, and intermediate/old
clusters. The relative timescales have been assessed by determining the
fractional population of sources at each evolutionary stage. Using the
evolutionary framework, we estimate the maximum age range of clusters in a
single SGMC is ~10 Myr, which suggests that the molecular gas is removed over
this timescale resulting in the cessation of star formation and the destruction
of the GMC within a radius of about 200 pc. (abridged)
