Figure 4

Particle-level snapshot data organization. Illustration of the scheme for particle/cell data within a snapshot for one particle type (e.g dark matter). Therein, particle order is set by a global sort of the following fields in this order: FoF group number, Subfind subhalo number, binding energy. As a result, FOF halos are contiguous, although they can span file chunks. Subfind subhalos are only contiguous within a single group, being separated between groups by an “inner fuzz” of all FOF particles not bound to any subhalo. “Outer fuzz” particles outside all halos are placed at the end of each snapshot