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How to get info and center of mass of halo from FoF and Subfind file? Keys?

Sophia Nasr
  • 17 Jan

Hello,

I've been trying to get the information from the FoF Subfind file I downloaded from the Illustris website, particularly, the center of mass for the specific snapshot I downloaded. I've not been able to find help on this, so I thought I'd post here.

My question: How do I access the keys in the FoF Subfind file, like I do in the snapshot I download (where the keys are "ParTypeX")? And once I do, how am I able to select my specific snapshot (for example, snapshot 3005) so that I can find out information on the center of mass of the halo?

To be clear, I downloaded the entire (I think 4 files) FoF Subfind file for z = 0 (the redshift I'm looking at), and the snapshot, I downloaded using the group catalog search and chose one that fits my mass requirements in the halos at z = 0.

Thank you very much!

Dylan Nelson
  • 17 Jan

Hi Sophia,

The best way to understand the structure of a HDF5 file is to run, at the command line:

h5ls file.hdf5
h5ls -r file.hdf5
Sophia Nasr
  • 17 Jan

Hi Dylan,

These look like Linux commands; I'm running a Windows machine. Would there be a way to do this in Windows?

Dylan Nelson
  • 1
  • 18 Jan

Maybe try HDF5View if you would like a GUI interface, otherwise you can also explore a file just with h5py in python.

Sophia Nasr
  • 1
  • 18 Jan

Thanks Dylan, I checked the link. I'll try that out and if I still have trouble I'll post for help here.

Sophia Nasr
  • 1
  • 23 Jan

Hi Dylan (or anyone reading this), I figured out how to use the files, thank you! What I'm now having trouble with is downloading new Illustris data: I see there's an option to "get" the snapshots we want, which comes with links to all the other files needed. I just don't know how to use "get" in Python, and the documentation I've found doesn't seem like it would help, since the "get" option is in json or api, and I'm not sure which I'm to use. I think figuring this one out might be my only option since clicking on the "group catalog search" where I can choose specific parameters I want included (ie, what stars data I'd like, what dark matter data, what gas data), which is the method I used before, when ticking off the items I want, the file size at the top doesn't shift from 0.00 MB, so that when I click download, nothing happens since there really isn't anything to download. Is there a problem with the servers? In any case, this makes me believe my best bet is to use the "get" option in Python (clicking the link with the subhalo file itself does nothing other than continually loading the page until it gets to a proxy error page that says there was an error reading the file from the server...).

I really appreciate the help, thanks so much!

Dylan Nelson
  • 23 Jan

Hi Sophia,

Downloading from the "group catalog search" page should work now, but you'll need to be careful to select only fields which exist in TNG (at the moment).

But yes, you should definitely download via a Python script in general, this is a more robust and serious approach. The get() is simply a user-defined function, as described in the Web API getting started guide.

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