Qualitative illustration of GC formation at high z through a minihalo–minihalo merger.

Formation rate of GCs through minihalo-minihalo mergers in the most massive dark matter halo of our simulation (Mh = 4.9×1012 M⊙ at z = 0). Data have been smoothed (boxcar filter width 50 Myr). At z > 5.5, N = 279 clusters are formed with ⟨z⟩ = 9.3 (dispersion ∆z = 1.9).

Cumulative number of GCs formed per unit volume (M pc−3 comoving) versus lookback time, for the two most massive halos of the simulated volume (solid/dashed blue), for the next three halos in mass ranking (solid, dotted and dashed red), and box-averaged value (black)..