Vol. 641
5. Galactic structure, stellar clusters and populations

The First Billion Years project: Finding infant globular clusters at z=6

Globular clusters (GCs) are among the oldest gravitationally bound stellar systems as they are characterized by stellar populations with ages of 11.5 to 12.5 Gyr. They probably formed during, or just after, the epoch of reionization; therefore, the study of these systems at high redshift cannot only give insight into the processes and environments that governed star formation at that time, but they can also represent valuable probes of the reionization epoch itself. In this work, the authors conduct an analysis of the demographics and global properties of low-mass stellar systems at high redshift, within the numerical framework of the FiBY cosmological simulations. They identify a population of dense objects with M*<10^4 Msolar, such that the fraction of baryons (over the total mass of baryons and dark matter) is close to unity; they suggest that these objects are possible infant GC candidates. Compared to present-day GCs in the local Universe, these infant GCs have a higher gas fraction and consistently appear to be more extended with the properties of the few examples of proto-globulars currently observed at high-redshift. Forthcoming studies will examine the origin and future evolution of these systems to further progress our understanding of the role of low-mass stellar systems in early galaxy formation.