Dark Matter Haloes¶

Source¶

Halo data is read from lhalo_binary merger tree files (trees_063.N). These are the same files consumed by SAGE26 at runtime.

Fields loaded by SAGE-Viewer¶

Field	Type	Units (raw)	Units (viewer)
`Pos[3]`	float32	Mpc/h	Mpc/h (unchanged)
`Mvir`	float32	10¹⁰ Msun/h	Msun (×1e10/h)
`SnapNum`	int32	—	—

Only Pos and Mvir are used for rendering. All other fields in the struct (Vel, Spin, VelDisp, Vmax, etc.) are read but discarded after the per-snapshot filter.

Mass floor¶

The default mass floor is 1e10 Msun. This removes very low-mass substructure that would otherwise dominate point count without contributing visible structure. Adjust with --min-halo-mass.

lhalo_binary file format¶

Each tree file has the following binary layout:

int32   nforests
int32   nhalos_total
int32[nforests]  nhalos_per_forest
HaloStruct[nhalos_total]

HaloStruct is 19 fields; the full dtype is defined in sage_viewer/io/halo_reader.py:HALO_DTYPE.

Parallel loading¶

SAGE-Viewer reads the N tree files in parallel (joblib). For miniMillennium with 8 files and 8 CPUs, all files load simultaneously.