  We use Atacama Large Millimeter Array CO(3-2) observations in conjunction
with optical observations from the Hubble Space Telescope to determine the
ratio of stellar to gas mass for regions in the Antennae Galaxies. We adopt the
term "instantaneous mass ratio" IMR(t) = M$_{stars}$/(M$_{gas}$ +M$_{stars}$),
that is equivalent to the star formation efficiency for an idealized system at
t = 0. We use two complementary approaches to determining the IMR(t) based on
1) the enclosed stellar and molecular mass within circular apertures centered
on optically-identified clusters, and 2) a tessellation algorithm that defines
regions based on CO emission. We find that only a small number of clusters
appear to have IMR(0) = SFE > 0.2, which suggests that only a small fraction of
these clusters will remain bound. The results suggest that by ages of
$10^{6.7}$ years, some clusters will have lost all of their associated
molecular gas, and by $10^{7.5}$ years this is true for the majority of
clusters. There appears to be slight dependence of the IMR(t) on the CO surface
brightness, which could support the idea that dense molecular environments are
more likely to form bound clusters. However, the IMR(t) appears to have a
strong dependence on extinction, which likely traces the evolutionary state of
clusters.

Astrophysics of Galaxies