How to get galaxy positions?

Murti Nauth
  • 7 Jul

I'd like to get the galaxy halo positions of TNG 100. I see you can download entire group catalogs, but I just want their Center of Mass Coordinates for every galaxy in each snapshot. Do you have any suggestions?

Dylan Nelson

Hi Murti,

You can request a download of a group catalog, only including one field. This is called {subset_query} if you search for it on the API reference documentation.

For example, for TNG100-1 at snapshot 99, you can download the SubhaloCM field with the following link:

www.tng-project.org/api/TNG100-1/files/groupcat-99/?Subhalo=SubhaloCM

(this is ~50 MB, and will take a second, as it is loading and combining all this data for the transfer)

Note that SubhaloCM is ok to use if you really want to, but generally we use SubhaloPos as the galaxy center position (less biased by asymmetric/distant particles in the subhalo).

Murti Nauth
  • 8 Jul

Oh i see, thank you. I was attempting to use the examples from the API documentation, but querying "Group=GroupPos," which was invalid.

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