I'm wanting to access the ID's of certain halos and subhalos from there group and sub catalog, but there does not seem to be a field to be able to access them. Is their a certain procedure when using group catalog?
Sorry Alexandres I don't quite understand what you're after. Do you mean, you want to access the properties of a halo/group given its "ID"? Most likely, you want to access the index of any of the HDF5 datasets corresponding to that "ID".
E.g., for the Group_M_Crit200 of "Halo ID=10" this is obtained by accessing Group/Group_M_Crit200, which is a 1D array of total size equal to the number of halos/groups in the catalog for that snapshot.
That's okay. I appreciate the help regardless. Thank you.