Public Data Access Overview / Discussion Forum

Dear Illustris team,

I am trying to download individual group catalog fields from IllustrisTNG simulations (e.g. TNG300-1) via the API, but all calls result in HTTP 500 Internal Server Error. The same API pattern seems to work correctly for the original Illustris simulations (Illustris-1).

Examples

TNG300-1 Snapshot 99 - GroupID field

curl -L -i -H "api-key: YOUR_API_KEY" \
  "https://www.tng-project.org/api/TNG300-1/files/groupcat-99/?Group=GroupID"

Response:

HTTP/1.1 302 Found
Date: Wed, 26 Nov 2025 13:34:26 GMT
Server: Apache
Strict-Transport-Security: max-age=63072000; preload
Location: https://data-eu.tng-project.org/file/groupcat/L205n2500TNG/99/req.Group.GroupID/?token=a1c6bc768c62957157ea
Content-Length: 0
Vary: Accept,Cookie
Allow: GET, HEAD, OPTIONS
X-Frame-Options: SAMEORIGIN
Content-Security-Policy: frame-ancestors https://*.tng-project.org;
Content-Type: text/html; charset=utf-8

HTTP/1.1 500 Internal Server Error
Date: Wed, 26 Nov 2025 13:34:27 GMT
Server: Apache
Content-Length: 0
X-Frame-Options: SAMEORIGIN
Content-Type: text/html; charset=utf-8
Connection: close

Similar API request for Illustris-1

curl -L -i -H "api-key: YOUR_API_KEY" \
  "https://www.tng-project.org/api/Illustris-1/files/groupcat-135/?Subhalo=SubhaloMass"

Response:

HTTP/1.1 302 Found
Date: Wed, 26 Nov 2025 13:35:34 GMT
Server: Apache
Strict-Transport-Security: max-age=63072000; preload
Location: https://data-eu.tng-project.org/file/groupcat/L75n1820FP/135/req.Subhalo.SubhaloMass/?token=36833d032e01978e2180
Content-Length: 0
Vary: Accept,Cookie
Allow: GET, HEAD, OPTIONS
X-Frame-Options: SAMEORIGIN
Content-Security-Policy: frame-ancestors https://*.tng-project.org;
Content-Type: text/html; charset=utf-8

HTTP/1.1 200 OK
Date: Wed, 26 Nov 2025 13:35:35 GMT
Server: Apache
Content-Length: 17498112
Content-Disposition: attachment; filename=groups_135.Subhalo.SubhaloMass.hdf5
X-Frame-Options: SAMEORIGIN
Content-Type: application/octet-stream

You are making requests for a single field of the catalogs (combining all the file chunks automatically).

In particular, Subhalo/SubhaloMass in your Illustris-1 example (which is valid), but for TNG300-1 you are asking for Group/GroupID (this does not exist). If you try something else e.g. Group/GroupMass, this works fine.

Thank you for your response. Indeed I mistook GroupID to be a field in the halo catalogs, sorry for my confusion. The other properties do work fine as you pointed out, thanks!