\textsc{CompaSO}: A new halo finder for competitive assignment to spherical overdensities

Understand

We describe a new method (\textsc{CompaSO}) for identifying groups of particles in cosmological $N$-body simulations.

• \textsc{CompaSO} builds upon existing spherical overdensity (SO) algorithms by taking into consideration the tidal radius around a smaller halo before competitively assigning halo membership to the particles.
• In this way, the \textsc{CompaSO} finder allows for more effective deblending of haloes in close proximity as well as the formation of new haloes on the outskirts of larger ones.
• This halo-finding algorithm is used in the \textsc{AbacusSummit} suite of $N$-body simulations, designed to meet the cosmological simulation requirements of the Dark Energy Spectroscopic Instrument (DESI) survey.