Do outer-fuzz BH particles have Host Halo Masses?

Anirban Chowdhary
  • 5
  • 6 Jun '23

Hi Everyone,

I am trying to study the clustering of AGNs using the Halo Occupation Distribution formalism. I am trying to calculate the Mean Occupation Function of AGNs and their redshift evolution.
My basic workflow requirements are as follows :

  1. I need to identify all the AGNs in the sample
  2. Categorise these AGNs into central and satellite AGNs , depending on if they are present in central or satellite galaxies.
  3. I need to link each AGN to their parent halos.
    (At this point I have A list of halos with their masses and the number of AGNs they host. The rest is very staright forward.)
  4. Divide the halos into different mass bins
  5. Find the average number of AGNs in every mass bin.
    The steps that I have done so far:
  6. I think identifying AGNs is fairly simple. I am selecting AGNs from the BH particles using Mass cuts and Luminosity Cuts(calculated using Mdot)
  7. Since there is no separate flag for centrals, I've added a flag to the most massive BH particle in each halo (to categorize central and satellite AGNs. (Note: I've used
    BH_HostHaloMass to list all BHs of the same halo)
    This is where I've encountered my first problem, rather a couple of doubts.
    1. Can I actually use the BH particles to select my AGNs? As some of them might be a part of the inner fuzz.
    2. Do I consider the BHs in that might be a part of the subhalos with PrimaryFlag value 0
    3. What should I do about the "outer fuzz" bh particles? Do they have any sort of HaloMass (or atleast a flag of some sort) assigned to them?

Please let me know if anyone knows how to handle this. Also I would like to hear out any other suggestions that could help me.


Dylan Nelson
  • 6 Jun '23

Is your objective an observational comparison, or a theoretical study?

If you are intending primarily to compare to observations, I would encourage you to select "central versus satellite AGNs" in the same way as the data (this will have nothing to do with subhalos, flags, fuzz, etc).

If you are just doing a theory study, I would suggest to write down a reasonable definition of central vs satellite AGN and apply that to all PartType5 particles.

The simplest definition would be: for each FoF halo, call its "main" SMBH the central, and any other satellites. Any SMBHs outside of FoF halos could also be called centrals.

By "main" you could use (a) most massive, as you describe above, (b) most massive within the central subhalo, (c) most central, (d) etc.

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