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Major mergers going Notts: challenges for modern halo finders

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


Peter Behroozi

Alexander Knebe

Frazer R. Pearce

Pascal Elahi

Jiaxin Han

Hanni Lux

Yao-Yuan Mao

Stuart I. Muldrew

Doug Potter

Chaichalit Srisawat


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.


Behroozi, P., Knebe, A., Pearce, F. R., Elahi, P., Han, J., Lux, H., …Srisawat, C. (2015). Major mergers going Notts: challenges for modern halo finders. Monthly Notices of the Royal Astronomical Society, 454(3),

Journal Article Type Article
Acceptance Date Aug 31, 2015
Publication Date Oct 16, 2015
Deposit Date May 3, 2017
Publicly Available Date May 3, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 454
Issue 3
Keywords methods: numerical, galaxies: haloes, dark matter
Public URL
Publisher URL


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