Halo catalogues

At each snapshot output by the simulation, bound objects are identified by grouping particles based on their spatial and dynamical properties. There are multiple methods for doing this, but within the FLAMINGO simulations structure is identified using the HBT-HERONS subhalo finder (Forouhar Moreno et al. 2025).

Once the centres of subhalos and the particles bound to each one have been identified, they are passed to the SOAP code (McGibbon et al. 2025).. This outputs catalogues containing a large number of properties for different halo/galaxy definitions, as described within the following pages.

• Halo catalogue directory layout
• SOAP halo variations
• SOAP property filters
• SOAP properties table
• Reading with swiftsimio
• Matching halos across simulations
• HBT-HERONS merger trees

Note

Within the cosmological simulation community people refer to both “halos” and “subhalos”, occasionally in an inconsistent manner. Within FLAMINGO a halo corresponds to an overdensity of particles, originally found using the 3D FoF algorithm. Each halo contains one or more subhalos, which are a self-bound collection of particles identified by HBT-HERONS. Subhalos can be either centrals (each halo has a single central subhalo, and the halo centre is defined as the position of the most bound particle of its central subhalo), or satellites.

The SOAP source code is available at on github and the exact git revision which was used to generate a halo catalogue can be found by inspecting the git_hash attribute of the Code group in the HDF5 halo catalogue file.