Sussing Merger Trees: Stability and Convergence

TL;DR

This study evaluates how output strategies and mass resolution affect the stability and convergence of dark matter halo merger trees, finding that more snapshots do not always improve tree completeness and that resolution impacts tree properties.

Contribution

It provides insights into optimal output strategies and the effects of mass resolution on merger tree construction, recommending integrated halo finding and tree-building methods.

Findings

More snapshots can shorten merger trees rather than extend them.

Patching schemes improve tree completeness by bridging dropouts.

Higher mass resolution leads to longer main branches and increased bushiness.

Abstract

Merger trees are routinely used to follow the growth and merging history of dark matter haloes and subhaloes in simulations of cosmic structure formation. Srisawat et al. (2013) compared a wide range of merger-tree-building codes. Here we test the influence of output strategies and mass resolution on tree-building. We find that, somewhat surprisingly, building the tree from more snapshots does not generally produce more complete trees; instead, it tends to short- en them. Significant improvements are seen for patching schemes which attempt to bridge over occasional dropouts in the underlying halo catalogues or schemes which combine the halo-finding and tree-building steps seamlessly. The adopted output strategy does not affec- t the average number of branches (bushiness) of the resultant merger trees. However, mass resolution has an influence on both main branch length and the bushiness. As the resolution increases, a halo with the same mass can be traced back further in time and will encounter more small progenitors during its evolutionary history. Given these results, we recommend that, for simulations intended as precursors for galaxy formation models where of order 100 or more snapshots are analysed, the tree-building routine should be integrated with the halo finder, or at the very least be able to patch over multiple adjacent snapshots.