Concentrations of Dark Haloes Emerge from Their Merger Histories

Understand

The concentration parameter is a key characteristic of a dark matter halo that conveniently connects the halo's present-day structure with its assembly history.

• Using 'Dark Sky', a suite of cosmological $N$-body simulations, we investigate how halo concentration evolves with time and emerges from the mass assembly history.
• We also explore the origin of the scatter in the relation between concentration and assembly history.
• We show that the evolution of halo concentration has two primary modes: (1) smooth increase due to pseudo-evolution; and (2) intense responses to physical merger events.