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arXiv · 2605.05622

The formation of the C-19 progenitor: a primordial cluster heated by gas expulsion

Zhen Wang·Long Wang·Zhen Yuan·Jiang Chang
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Abstract

The extremely metal-poor nature of the C-19 stream indicates that its progenitor was a primordial stellar system born in the very early Universe. Current observations show that it has a small metallicity dispersion (0.18 at the 95% confidence level), which is the signature of a globular cluster origin, while at the same time displaying an unusually large velocity dispersion ($\sim10$ km/s) typical of dwarf galaxies. To reconcile this conflicting observational evidence, previous simulations have focused on potential interactions with dark matter subhalos, which can efficiently make a cluster stream dynamically hot. In this work, we explore internal dynamical processes in star cluster formation, focusing on initial conditions shaped by gas expulsion and a top-heavy initial mass function. We find that the large observed velocity dispersion and broad stream morphology can be reproduced by a cluster that underwent severe gas expulsion and expansion during its birth phase, which is potentially a typical formation scenario of extremely metal-poor star clusters. A top-heavy IMF and binaries can also increase the velocity dispersion. The formation of C-19 may involve a combination of these effects.

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Zhen Wang, Long Wang, Zhen Yuan, Jiang Chang. 2026-05-07. The formation of the C-19 progenitor: a primordial cluster heated by gas expulsion. https://arxiv.org/abs/2605.05622

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