Is there a way to access the Subfind ID of the next progenitor of a galaxy from the web based API or group catalogues? I'm a novice programmer and am trying to do this without coding, at least at first to get an idea of where the information is and how I want to use it.
You can get this from the web API. Tasks #8 and #9 in the cookbook walk down the descendants in this manner, but you can replace sublink_descendant with sublink_progenitor to do the other direction.
The value of the Subfind ID of the progenitor is called prog_sfid and its snapshot `prog_snap'. For example, for Subhalo #5555 at Snapshot 135 of Illustris-1, this is Subfind ID 5634 at snapshot 134 (it is usually, though not always, one snapshot prior. The progenitor could sometimes be two snapshots back).
This information is not available in the group catalogs, it is instead in the "merger trees", which you could additionally download, but the web API will be easier to start.
Thank you very much! I'll be sure to use those tasks. Any tips on accessing the next progenitor, not just the first progenitor?
Apologies, I realize I misread your question. For the next progenitors (branches other than the main branch), you will need to download the merger tree - these links aren't available in the web API.
If you use the sublink.loadTree() function, the return will include all branches, following both first and next progenitor links.
Perhaps if you have some idea of what you're after I can try to be more specific.
Thanks a lot, I have downloaded the merger tree for a sample subhalo, and have figured out how to read it by hand. I'll work on creating an algorithm for tracing it.