Matching objects between supplementary catalog and group catalog
wang zuolei
28 Mar '22
Hello,I want to get the location of each galaxy in the file(hih2_galaxy_099 .hdf5),but it doesn't have the location information, so I try to use the file(fof_subhalo_tab_099.**.hdf5) and match the location by ID, but, the ids of the two files don't match,'id_subhalo'and'SubhaloID' why don't the two ids match?
That's right, the idea is that not every subhalo exists in the hih2_galaxy files. So, the id_subhalo field gives you the list of subhalo IDs, for which data exists.
(This is true for almost all "supplementary data catalogs", and the corresponding field is often called SubfindID or SubhaloID).
Then if you want the positions of these subhalos (or any other property), you should load the group catalogs, and take the corresponding entries.
wang zuolei
29 Mar '22
fof_subhalo_tab * does not give the 'field' associated with the ID of these subhalos,fof_subhalo_tab * has 4371211 subhalos, their IDs is 0 through 4371210, right?
Dylan Nelson
29 Mar '22
That's correct, the term "ID" is always used to mean the index (for all datasets) in the group catalogs (fof_subhalo_tab* files).
wang zuolei
29 Mar '22
Thank you, Dylan!
Alice Chen
2 Apr
Sorry just to follow up on this a bit, does the subhalo ID for each halo change from snapshot to snapshot? Or if we're looking at a single subhalo evolution at different redshifts (different snapshots), would that subhalo have the same subhalo ID in each snapshot?
Dylan Nelson
2 Apr
It's important that there is no relation at all between subhalo IDs in different snapshots. The ID of a subhalo will, in general, always change with time.
The only way to connect subhalos at different snapshots is to use something like the merger tree.
Alice Chen
2 Apr
That's good to know about the subhalo ID. Thank you for clarifying!
Hello,I want to get the location of each galaxy in the file(hih2_galaxy_099 .hdf5),but it doesn't have the location information, so I try to use the file(fof_subhalo_tab_099.**.hdf5) and match the location by ID, but, the ids of the two files don't match,'id_subhalo'and'SubhaloID' why don't the two ids match?
Thank you in advance
That's right, the idea is that not every subhalo exists in the
hih2_galaxyfiles. So, theid_subhalofield gives you the list of subhalo IDs, for which data exists.(This is true for almost all "supplementary data catalogs", and the corresponding field is often called
SubfindIDorSubhaloID).Then if you want the positions of these subhalos (or any other property), you should load the group catalogs, and take the corresponding entries.
fof_subhalo_tab * does not give the 'field' associated with the ID of these subhalos,fof_subhalo_tab * has 4371211 subhalos, their IDs is 0 through 4371210, right?
That's correct, the term "ID" is always used to mean the index (for all datasets) in the group catalogs (fof_subhalo_tab* files).
Thank you, Dylan!
Sorry just to follow up on this a bit, does the subhalo ID for each halo change from snapshot to snapshot? Or if we're looking at a single subhalo evolution at different redshifts (different snapshots), would that subhalo have the same subhalo ID in each snapshot?
It's important that there is no relation at all between subhalo IDs in different snapshots. The ID of a subhalo will, in general, always change with time.
The only way to connect subhalos at different snapshots is to use something like the merger tree.
That's good to know about the subhalo ID. Thank you for clarifying!