Galaxies¶
Source¶
Galaxy data is read from the SAGE HDF5 output file (model_0.hdf5). The file is structured as one HDF5 group per snapshot: Snap_0, Snap_1, …, Snap_63.
Fields loaded by ViSAGE¶
| HDF5 field | Type | Raw units | Viewer units |
|---|---|---|---|
Posx, Posy, Posz |
float32 | Mpc/h | Mpc/h |
StellarMass |
float32 | 10¹⁰ Msun/h | Msun (×1e10/h) |
Mvir |
float32 | 10¹⁰ Msun/h | kept raw for masking |
SfrDisk + SfrBulge |
float32 | Msun/yr | summed → total SFR |
Type |
int32 | — | 0=central, 1+=satellite |
Derived quantity: sSFR = (SfrDisk + SfrBulge) / StellarMass in yr⁻¹.
Galaxy types¶
| Type value | Meaning |
|---|---|
| 0 | Central galaxy — sits at the potential minimum of its FOF group |
| 1 | Satellite — orbiting within another halo |
| 2+ | Orphan satellite — lost its subhalo, tracked by SAGE26 merger timer |
In type colour mode, centrals are shown in Blues and satellites in Reds.
Mass floor¶
The stellar mass floor follows the simulation's resolution: per snapshot, the stellar mass from which 90% of central galaxies live in haloes of at least 20 particles (or 50 or 100: Resolved haloes on the setup screens, or --min-particles). Galaxies with Mvir = 0 are also excluded (they have no associated halo). A fixed floor can be set with --min-stellar-mass.
SAGE26 output format reference¶
The full 84-field SAGE HDF5 schema is documented in the SAGE26 output reference. ViSAGE uses only the 8 fields above; all others are available in the file for custom scripting via the Python API.