Star clusters at cosmic dawn I: the emergence of the initial cluster mass function
Abstract
JWST observations of lensed galaxies reveal unusually bright star-cluster candidates within the first billion years after the Big Bang. However, the physical processes shaping the initial cluster mass function (ICMF) remain uncertain. We study the formation of a galaxy embedded in a dark matter halo whose virial mass reaches 1010 M⊙ at z=6, using cosmological radiation-hydrodynamics zoom-in simulations. Its star clusters, represented by sink particles, accrete gas and form stellar populations that supply radiation and supernova feedback, thereby regulating their own growth. As we do not prescribe an efficiency per free-fall time or a fixed star-cluster formation duration, the ICMF emerges self-consistently. We assess the effects of numerical resolution and stellar radiation. Schechter fits to the central-galaxy ICMF give truncation masses near 6 × 106 M⊙, with substantial uncertainty. At fixed resolution, including stellar radiation makes the low-mass slope of the ICMF shallower, from −1.60 to −1.34, while doubling the spatial resolution steepens it back to −1.54. Stellar radiation also reduces the abundance of low-mass clouds, particularly those with lower gas densities, and shortens the formation time of star clusters to about a Myr, i.e. well before their first supernovae go off. On average, more rapidly fed star clusters accrete for longer, making their final masses rise faster than linearly with the initial accretion rate and contributing to a flatter ICMF. At fixed host-galaxy star formation rate, our brightest simulated clusters reach UV luminosities comparable to those of observed lensed star-cluster candidates.
Related
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BibTeX
@misc{thompson2026star,
title = {{Star clusters at cosmic dawn I: the emergence of the initial cluster mass function}},
author = {Fred S. Thompson and Julien Devriendt and Adrianne Slyz and Taysun Kimm and Cheonsu Kang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32497},
eprint = {2610.32497},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32497},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Star clusters at cosmic dawn I: the emergence of the initial cluster mass function
AU - Fred S. Thompson
AU - Julien Devriendt
AU - Adrianne Slyz
AU - Taysun Kimm
AU - Cheonsu Kang
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32497
UR - https://arxiv.org/abs/2610.32497
AB - JWST observations of lensed galaxies reveal unusually bright star-cluster candidates within the first billion years after the Big Bang. However, the physical processes shaping the initial cluster mass function (ICMF) remain uncertain. We study the formation of a galaxy embedded in a dark matter halo whose virial mass reaches 10^10 M_⊙ at z=6, using cosmological radiation-hydrodynamics zoom-in simulations. Its star clusters, represented by sink particles, accrete gas and form stellar populations that supply radiation and supernova feedback, thereby regulating their own growth. As we do not prescribe an efficiency per free-fall time or a fixed star-cluster formation duration, the ICMF emerges self-consistently. We assess the effects of numerical resolution and stellar radiation. Schechter fits to the central-galaxy ICMF give truncation masses near 6 × 10^6 M_⊙, with substantial uncertainty. At fixed resolution, including stellar radiation makes the low-mass slope of the ICMF shallower, from −1.60 to −1.34, while doubling the spatial resolution steepens it back to −1.54. Stellar radiation also reduces the abundance of low-mass clouds, particularly those with lower gas densities, and shortens the formation time of star clusters to about a Myr, i.e. well before their first supernovae go off. On average, more rapidly fed star clusters accrete for longer, making their final masses rise faster than linearly with the initial accretion rate and contributing to a flatter ICMF. At fixed host-galaxy star formation rate, our brightest simulated clusters reach UV luminosities comparable to those of observed lensed star-cluster candidates.
ER -