How to find subhalo(galaxy) IDs

Zhiyuan Ji
  • 4 Apr '21

Hi, I get confused about how to find subhalo IDs which should be used to track their formation histories.
For example, I am interested in the quiescent galaxies at z=2 (snapnum=33) in TNG100-3. I can use "groupcat.loadSubhalos" to first check sSFR-Mstar distribution of all galaxies. Then, say, I am only interested in those with sSFR<1e-10. Because I don't see "subhaloID", "SubfindID" or "id" existing in the field options of "Subfind Subhalos", I am not sure how to find the Subhalo IDs for those galaxies. I did notice that the "count" (or, index) of the data array returned from "groupcat.loadSubhalos" seems to be the same as the "ID" returned from the web-based "Search galaxy/subhalo catalogs". But I don't know that if the count/index is the "SubhaloID" and should be used for SubLink to extract its formation history. Thanks in advance

Dylan Nelson
  • 5 Apr '21


The "ID" is the same as the "index". For example,

sfr = il.groupcat.loadSubhalos(basePath,33,fields=['SubhaloSFRinRad'])
subhalo_ids = np.where( sfr < 0.1 )[0]

for subhalo_id in subhalo_ids:
    tree = il.sublink.loadTree(basePath,33,subhalo_id,fields=fields,onlyMPB=True)
Zhiyuan Ji
  • 5 Apr '21

Thanks, Dylan!

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