About the meaning of the SubhaloParent

jose benavides
  • 8 Jul '18

My name is Jose Benavides, a PhD student at the Universidad Nacional de Córdoba (Argentina). I notice that within a FoF group their SubhaloParent index can take a value from 0 to any number, but not necessarily all numbers exist in this range (for example: there are subhalos with Parent 0,1,2,6,10,12, .. ., but there is no 3,4,5,7,8,9,11, ...) why? What does it mean that the members of a group have associated a SubhaloParent 0 or 1 or 2, ...? There may even be a single subhalo with a unique parent number. Initially we think that these parent indexes refer to substructures within the FoF groups (giving them a more physical criterion), something like:

Subhalos with SubhaloParent = 0 to a "subgroup 0" within the "groupFoF 0" (for example: SubhaloGrNr == 0 in a specific snap)),

Subhalos with SubhaloParent = 1 to a "subgroup 1" within "groupFoF 0" (for example: SubhaloGrNr == 0 in a specific snap)),

and so on.

I am not sure if we are going the right way, I would appreciate it if you can give me some help about the meaning (physical or computational for example) of this SubhaloParent.

Cordial greetings and thanks,


Dylan Nelson
  • 13 Jul '18

Hi Jose,

The description of SubhaloParent which I suspect you've already seen is:

Index into the Subhalo table of the unique SUBF host/parent of this Subhalo. This index is local to the group (i.e. 2 indicates the third most massive subhalo of the parent halo of this subhalo, not the third most massive of the whole snapshot). The values are often zero for all subhalos of a group, indicating that there is no resolved hierarchical structure in that group, beyond the primary subhalo having as direct children all of the secondary subhalos.

Note that we very rarely use this field - it would only be needed if you are searching for subhalos of subhalos (i.e. hierarchical substructure). Perhaps if you can say more what you are trying to do, I can suggest something.

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