Formation of Compact Stellar Clusters by High-Redshift Galaxy Outflows I: Nonequillibrium Coolant Formation

TL;DR

This study uses high-resolution simulations to show how galaxy outflows at high redshift can trigger the formation of compact, globular-cluster-like stellar groups from primordial clouds through non-equilibrium molecular cooling.

Contribution

It demonstrates that outflow-induced shocks can convert minihaloes into compact star clusters with properties similar to globular clusters, emphasizing the role of non-equilibrium chemistry.

Findings

Minihaloes can form star clusters triggered by galaxy outflows.

Clusters are less than 10^6 solar masses and ejected from dark matter halos.

Non-equilibrium molecular cooling is crucial for star formation in this context.

Abstract

We use high-resolution three-dimensional adaptive mesh refinement simulations to investigate the interaction of high-redshift galaxy outflows with low-mass virialized clouds of primordial composition. While atomic cooling allows star formation in objects with virial temperatures above $10^4$ K, "minihaloes" below this threshold are generally unable to form stars by themselves. However, these objects are highly susceptible to triggered star formation, induced by outflows from neighboring high-redshift starburst galaxies. Here we conduct a study of these interactions, focusing on cooling through non-equilibrium molecular hydrogen (H$_2$) and hydrogen deuteride (HD) formation. Tracking the non-equilibrium chemistry and cooling of 14 species and including the presence of a dissociating background, we show that shock interactions can transform minihaloes into extremely compact clusters of coeval stars. Furthermore, these clusters are all less than $\approx 10^6 M_\odot,$ and they are ejected from their parent dark matter halos: properties that are remarkably similar to those of the old population of globular clusters.