$\Lambda$CDM star clusters at cosmic dawn: stellar densities, environment, and equilibrium

TL;DR

This paper uses cosmological simulations to study the formation and properties of high-redshift star clusters, revealing their potential to reach extreme densities and providing predictions relevant for JWST observations.

Contribution

It introduces a new simulation approach focusing on baryonic structures to analyze early star cluster formation at high redshift, offering insights into their densities and dynamical states.

Findings

High-z star clusters can reach extreme surface densities.

Simulations predict observable properties consistent with JWST data.

Early star clusters may preserve hierarchical formation evidence.

Abstract

The James Webb Space Telescope (JWST) has opened a window on many new puzzles in the early Universe, including a population of high-redshift star clusters with extremely high stellar surface density, suggesting unique star formation conditions in the Universe's early evolution. We study the formation and evolution of these first star clusters and galaxies using an AREPO cosmological simulation box designed to resolve the intricate environments of the smallest halos hosting Population III star clusters at $z \geq 12$. Our approach, which prioritizes baryonic structure identification through a friends-of-friends algorithm, provides new insights into early star cluster formation and delivers predictions directly relevant to observations. We investigate the dynamical properties of these first star clusters and use numerical and analytical methods to understand the populations of virialized and non-virialized systems. Our findings indicate that high-$z$ star clusters in a feedback-free regime can achieve extreme surface densities, consistent with the systems detected by JWST. These results imply that JWST may have the opportunity to uncover stellar systems at high redshift whose dynamical state preserves evidence of the hierarchical structure formation process.