The formation of secondary stellar generations in massive young star
  clusters from rapidly cooling shocked stellar winds
  We study a model of rapidly cooling shocked stellar winds in young massive
clusters and estimate the circumstances under which secondary star formation,
out of the reinserted winds from a first stellar generation (1G), is possible.
We have used two implementations of the model: a highly idealized
computationally inexpensive spherically symmetric semi-analytic model, and a
complex three-dimensional radiation-hydrodynamic simulations, and they are in a
good mutual agreement. The results confirm our previous findings that in a
cluster with 1G mass $10^7$ M$_\odot$ and half-mass radius $2.38$ pc, the
shocked stellar winds become thermally unstable, collapse into dense gaseous
structures that partially accumulate inside the cluster, self-shield against
ionizing stellar radiation and form the second generation (2G) of stars. We
have used the semi-analytic model to explore a subset of the parameter space
covering a wide range of the observationally poorly constrained parameters: the
heating efficiency, $\eta_\mathrm{he}$, and the mass loading,
$\eta_\mathrm{ml}$. The results show that the fraction of the 1G stellar winds
accumulating inside the cluster can be larger than $50$ % if $\eta_\mathrm{he}
\lesssim 10$ % which is suggested by the observations. Furthermore, for low
$\eta_\mathrm{he}$, the model provides a self-consistent mechanism predicting
2G stars forming only in the central zones of the cluster. Finally, we have
calculated the accumulated warm gas emission in the H30$\alpha$ recombination
line, analyzed its velocity profile and estimated its intensity for super star
clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas
should be detectable with ALMA.
