  The fraction of star formation that results in bound star clusters is
influenced by the density spectrum in which stars are formed and by the
response of the stellar structure to gas expulsion. We analyse hydrodynamical
simulations of turbulent fragmentation in star-forming regions to assess the
dynamical properties of the resulting population of stars and (sub)clusters.
Stellar subclusters are identified using a minimum spanning tree algorithm.
When considering only the gravitational potential of the stars and ignoring the
gas, we find that the identified subclusters are close to virial equilibrium
(the typical virial ratio Q_vir~0.59, where virial equilibrium would be
Q_vir~0.5). This virial state is a consequence of the low gas fractions within
the subclusters, caused by the accretion of gas onto the stars and the
accretion-induced shrinkage of the subclusters. Because the subclusters are
gas-poor, up to a length scale of 0.1-0.2 pc at the end of the simulation, they
are only weakly affected by gas expulsion. The fraction of subclusters that
reaches the high density required to evolve to a gas-poor state increases with
the density of the star-forming region. We extend this argument to star cluster
scales, and suggest that the absence of gas indicates that the early disruption
of star clusters due to gas expulsion (infant mortality) plays a smaller role
than anticipated, and is potentially restricted to star-forming regions with
low ambient gas densities. We propose that in dense star-forming regions, the
tidal shocking of young star clusters by the surrounding gas clouds could be
responsible for the early disruption. This `cruel cradle effect' would work in
addition to disruption by gas expulsion. We suggest possible methods to
quantify the relative contributions of both mechanisms.
