Major Mergers Going Notts: Challenges for Modern Halo Finders

Understand

Merging haloes with similar masses (i.e., major mergers) pose significant challenges for halo finders.

• We compare five halo finding algorithms' (AHF, HBT, Rockstar, SubFind, and VELOCIraptor) recovery of halo properties for both isolated and cosmological major mergers.
• We find that halo positions and velocities are often robust, but mass biases exist for every technique.
• The algorithms also show strong disagreement in the prevalence and duration of major mergers, especially at high redshifts (z>1).