Major mergers going Notts: Challenges for modern halo finders

Peter Behroozi, Alexander Knebe, Frazer R. Pearce, Pascal Elahi, Jiaxin Han, Hanni Lux, Yao Yuan Mao, Stuart I. Muldrew, Doug Potter, Chaichalit Srisawat

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


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). This raises significant uncertainties for theoretical models that require major mergers for, e.g. galaxy morphology changes, size changes, or black hole growth, as well as for finding Bullet Cluster analogues. All finders not using temporal information also show host halo and subhalo relationship swaps over successive timesteps, requiring careful merger tree construction to avoid problematic mass accretion histories. We suggest that future algorithms should combine phase-space and temporal information to avoid the issues presented.

Original languageEnglish (US)
Pages (from-to)3020-3029
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Dec 11 2015
Externally publishedYes


  • Dark matter
  • Galaxies: haloes
  • Methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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