Formation of compact stellar clusters by high-redshift galaxy outflows. I. Non-equilibrium coolant formation

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 10⁴ K, "minihalos" 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 (H2) 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 minihalos into extremely compact clusters of coeval stars. Furthermore, these clusters are all less than ≈a10⁶M_⊙, and they are ejected from their parent dark matter halos: properties that are remarkably similar to those of the old population of globular clusters.