The efficiency of star formation in clustered and distributed regions
  We investigate the formation of both clustered and distributed populations of
young stars in a single molecular cloud. We present a numerical simulation of a
10,000 solar mass elongated, turbulent, molecular cloud and the formation of
over 2500 stars. The stars form both in stellar clusters and in a distributed
mode which is determined by the local gravitational binding of the cloud. A
density gradient along the major axis of the cloud produces bound regions that
form stellar clusters and unbound regions that form a more distributed
population. The initial mass function also depends on the local gravitational
binding of the cloud with bound regions forming full IMFs whereas in the
unbound, distributed regions the stellar masses cluster around the local Jeans
mass and lack both the high-mass and the low-mass stars. The overall efficiency
of star formation is ~ 15 % in the cloud when the calculation is terminated,
but varies from less than 1 % in the the regions of distributed star formation
to ~ 40 % in regions containing large stellar clusters. Considering that large
scale surveys are likely to catch clouds at all evolutionary stages, estimates
of the (time-averaged) star formation efficiency for the giant molecular cloud
reported here is only ~ 4 %. This would lead to the erroneous conclusion of
'slow' star formation when in fact it is occurring on a dynamical timescale.
