The formation of secondary stellar generations in massive young star clusters from rapidly cooling shocked stellar winds

Abstract

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.

18 pages, 10 figures, accepted by ApJ

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