Black Holes linked to Subhalos

Kate Attard
  • 15 Aug '20

Hi,

I was wondering if there was a way to link the black hole information provided in the supplementary data catalogue (the Blackhole details catalogue) to specific subhalos - for example, the black hole IDs and coordinates to the subhalo ID which they belong to (where one applies).

Many thanks,
Kate

Dylan Nelson
  • 15 Aug '20

Hi Kate,

Yes I would suggest to do this by "ID". You can load all PartType5/ParticleIDs from the snapshot, and then search in this array (it is quite small) for the ID of the black hole of interest. Once you've found it, you have the snapshot index of this particle. Then the problem is the same for any particle of any type: given its index in the snapshot, what subhalo contains it? The answer would be the largest entry in offsets.hdf5/Subhalo/SnapByType which is smaller than the index. A similar logic is used in many places in the example scripts for loading purposes.

Kate Attard
  • 27 Aug '20

Hi Dylan,

Thanks for your reply; just to clarify, does this approach work for the original Illustris data as well as for the IllustrisTNG data (where the offset files can be downloaded)?

Many thanks,
Kate

Dylan Nelson
  • 29 Aug '20

That's correct, the same offsets exist for original Illustris, they are just included in the group catalog files, instead of as separate files.

Majda Smole
  • 30 Sep

Hello,

I want to link BHs from BH mergers supplementary catalog of TNG300-1 simulations with the associated subhalos. To do that, I followed instructions given above. However, I got somewhat unexpected results. Is there any way I can check if I linked BHs with subhalos correctly? Right now I am just able to compare BH masses prior a BH merger (from the supplementary catalog) to total masses of all BH particles in the given subhalo.

Here is one example that drew my attention, a merger pair from the catalog:

id_in 118620622517
id_out 119152051994
snapshot_merger 33

I found that BH 119152051994 occupies subhalo 123104 at snapshot 33, while id_in is not linked to any subhalo (that is what I get for all id_in BHs, at all snapshots but I guess that is not an issue since id_in BHs merge with id_out?).

However, when I check this subhalo using api https://www.tng-project.org/api/TNG300-1/snapshots/33/subhalos/123104/
I get that the given halo does not have any BH. At snapshot 32 bh_in occupied subhalo 115103, and bh_out subhalo 115106, which both host a BH.

Any feedback would be much appreciated,
Thanks in advance,
Majda

Dylan Nelson
  • 30 Sep

Hi Majda,

Please see a more complete code snippet on this thread.

In particular, I see that TNG300-1 snapshot 33 BH ID 119152051994 is actually in no subhalo. It is in halo 932. So, it must have gotten unbound from its subhalo and is now somewhat in the outskirts (I would guess).

Ideally, this should be rare (true for 0.018% of BHs at this snap), i.e. this isn't particularly good or physical behavior, because the model we have for the dynamics of BHs isn't really good enough to resolve wandering/runaway BHs which get far from their center. I would suggest to filter out and ignore such cases, if you need to. In general, BHs should sit near the center of their subhalo.

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