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

TL;DR

This study models how rapidly cooling shocked stellar winds in young massive clusters can lead to secondary star formation, supported by simulations and semi-analytic models, with observable predictions for ALMA.

Contribution

It introduces a combined semi-analytic and 3D radiation-hydrodynamic model to explore conditions for secondary star formation in massive clusters, emphasizing the role of wind cooling and parameter effects.

Findings

Shocked stellar winds become thermally unstable and form dense structures.

More than 50% of stellar winds can accumulate inside the cluster under certain conditions.

Predicted warm gas emission is detectable with ALMA in specific galaxy clusters.

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.