Public Data Access Overview / Discussion Forum

Hi! I need to get all the subfindIDs of the progenitors for a given subhalo. Just to make sure I understand it correctly. My understanding goes as follows,

• If onlyMPB=True, we will get the subfindID and corresponding snapNum of the main progenitors.
• If onlyMPB=False, we will get all the subfindID and corresponding snapNum of the whole progenitors.
  When I want to check all the progenitors at snapNum=98, I just need to check the output of tree1 and select all the subfindID with snapNum=98?

Many thanks!

That's right, with onlyMPB=False you load the entire tree, and all the subhalos you find at snap 98 are the progenitors of your snap 99 subhalo.

The diagram in the documentation should also help.

Thanks! By the way, I wanna ask that what is the usage of the subhaloID in a tree? In my understanding, it can be just used to locate a subhalo in the tree and we cannot load a corresponding subhalo or its gas particles by the subhaloID in the tree only.

The SubhaloID field of the merger tree is a unique ID, internal to the trees.

You can access the corresponding ID of the subhalo, needed to e.g. load its gas cells form the snapshot, with the SubfindID field.