Dynamical Simulations of the First Globular Clusters

TL;DR

This study uses dynamical simulations to explore how the initial conditions and redshift of formation influence the structure and distribution of globular clusters and their stellar streams within dark matter halos.

Contribution

It provides new insights into the formation and evolution of globular clusters in high redshift dark matter sub-halos, highlighting the impact of formation time and sub-halo mass.

Findings

Clusters from low mass sub-halos have more extended stellar distributions.

Higher redshift formation results in more compact clusters.

Clusters formed at redshift >4 match observed Milky Way sizes.

Abstract

Tidally limited star clusters are started on nearly circular orbits in the dark matter sub-halos present at high redshift and evolved with an n-body code augmented with gravitational interactions in the clusters. The tidally removed stars and the remaining high redshift clusters from a redshift 8 start are more concentrated than the dark matter, as expected. However, the subset of stars from the clusters that began in the lower mass sub-halos have a distribution somewhat more extended than the dark matter halo, with a mean galactic radius of about 60 kpc inside 150 kpc. The clusters from low mass sub-halos, those with a peak circular velocity of $ 12-18$ \kms, also produce most of the population's thin stellar streams. The dependence of the stellar population distribution on sub-halo mass is not seen in simulations that start clusters at lower redshift. The half mass radii of the clusters are set by the tidal fields of the initial cluster orbits, which leads to the average half mass radius decreasing with increased redshift of formation. Starting clusters at greater than redshift 4 leads to cluster half mass radii approximately as seen in the Milky Way, with lower redshifts leading to clusters that are too large. If extremely metal poor globular clusters were preferentially formed in high redshift, low mass, dwarf galaxies, then the clusters should be spread nearly uniformly over the dark halo, along with their tidally removed stars.