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Halo merger tree comparison: impact on galaxy formation models

Gómez, Jonathan S; Padilla, ND; Helly, JC; Lacey, CG; Baugh, CM; Lagos, CDP

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Jonathan S Gómez

ND Padilla

CDP Lagos


We examine the effect of using different halo finders and merger tree building algorithms on galaxy properties predicted using the GALFORM semi-analytical model run on a high resolution, large volume dark matter simulation. The halo finders/tree builders HBT, ROCKSTAR, SUBFIND, and VELOCI RAPTOR differ in their definitions of halo mass, on whether only spatial or phase-space information is used, and in how they distinguish satellite and main haloes; all of these features have some impact on the model galaxies, even after the trees are post-processed and homogenized by GALFORM. The stellar mass function is insensitive to the halo and merger tree finder adopted. However, we find that the number of central and satellite galaxies in GALFORM does depend slightly on the halo finder/tree builder. The number of galaxies without resolved subhaloes depends strongly on the tree builder, with VELOCIRAPTOR, a phase-space finder, showing the largest population of such galaxies. The distributions of stellar masses, cold and hot gas masses, and star formation rates agree well between different halo finders/tree builders. However, because VELOCIRAPTOR has more early progenitor haloes, with these trees GALFORM produces slightly higher star formation rate densities at high redshift, smaller galaxy sizes, and larger stellar masses for the spheroid component. Since in all cases these differences are small we conclude that, when all of the trees are processed so that the main progenitor mass increases monotonically, the predicted GALFORM galaxy populations are stable and consistent for these four halo finders/tree builders.


Gómez, J. S., Padilla, N., Helly, J., Lacey, C., Baugh, C., & Lagos, C. (2022). Halo merger tree comparison: impact on galaxy formation models. Monthly Notices of the Royal Astronomical Society, 510(4), 5500-5519.

Journal Article Type Article
Acceptance Date Dec 10, 2021
Online Publication Date Dec 16, 2021
Publication Date 2022-03
Deposit Date May 26, 2022
Publicly Available Date May 26, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 510
Issue 4
Pages 5500-5519


Published Journal Article (3.6 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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