Energy budget of forming clumps in numerical simulations of collapsing
  clouds
  We analyze the physical properties and energy balance of density enhancements
in two SPH simulations of the formation, evolution, and collapse of giant
molecular clouds. In the simulations, no feedback is included, so all motions
are due either to the initial, decaying turbulence, or to gravitational
contraction. We define clumps as connected regions above a series of density
thresholds. The resultingfull set of clumps follows the generalized
energy-equipartition relation $\sigma_{v}/R^{1/2} \propto \Sigma^{1/2}$, where
$\sigma_{v}$ is the velocity dispersion, $R$ is the "radius", and $\Sigma$ is
the column density. We interpret this as a natural consequence of gravitational
contraction at all scales, rather than virial equilibrium. Nevertheless, clumps
with low $\Sigma$ tend to show a large scatter around equipartition. In more
than half of the cases, this scatter is dominated by external turbulent
compressions that {\it assemble} the clumps, rather than by small-scale random
motions that would disperse them. The other half does actually disperse.
Moreover, clump sub-samples selected by means of different criteria exhibit
different scalings. Sub-samples with narrow $\Sigma$ ranges follow Larson-like
relations, although characterized by their respective value of $\Sigma$.
Finally, we find that: i) clumps lying in filaments tend to appear sub-virial;
ii) high-density cores ($n \ge 10^5$ cm$^3$) that exhibit moderate kinetic
energy excesses often contain sink ("stellar") particles, and the excess
disappears when the stellar mass is taken into account in the energy balance;
iii) cores with kinetic energy excess but no stellar particles are truly in a
state of dispersal.
