SubhaloFalg in merger tree

Yu-Hsiu Huang
  • 23 Mar '20

Hi Dylan,

I have some naive questions about SubhaloFlag.

  1. In merger trees, there isn't SubhaloFlag available. Are all the subhalos contained in merger trees of cosmological origin?

  2. If not, is there any efficient way to download the SubhaloFlag in merger trees instead of from the group catalog? And, If a subhalo is classified as non-cosmological origin in merger trees (SubhaloFlag==0), what is the meaning of merge this subhalo with other subhalos that are considered as galaxies of cosmological origin?


Dylan Nelson
  • 24 Mar '20


Unfortunately SubhaloFlag is not generally available in the merger trees, only the group catalogs.

So I would download this field (only) from the group catalogs at all snapshots. You can download subsets of the group catalogs, one field at a time. For the details, search for {subset_query} on the API documentation page. Then you can check the SubhaloFlag of a subhalo given its SnapNum and SubfindID from the tree.

Mergers with such "non-cosmological" objects should be fairly common. For instance, if this structure resulted from the fragmentation of a disk, and is a clump of gas or stars orbiting around (or in) a galaxy, then as soon as it gets disrupted or destroyed, and its particles then become part of the galaxy subhalo, this would satisfy the typical conditions for a "merger". If you don't want these events, you could filter them out.

Yu-Hsiu Huang
  • 26 Mar '20

Thanks a lot.

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