For stellar particles of each galaxy, it seems that they have their IDs in TNG. Will stellar particle ID change like sublink ID for galaxy as snap increases?
No, once a star particle is formed and given an ID, it keeps that ID for the future. Star particles cannot be destroyed, so you should be able to find this same ID in all future snapshots.
Note however a small caveat: because of stellar mass loss, a fraction of the mass in the star particle will be (slowly) transferred back into the gas. The only way to track the flow of this baryonic material would be to use the tracer particles.
Thank you for your reply! So is it possible for me to know the merger history of a galaxy from its star particle? I have a thought: get the stellar particle ID of the galaxy at snap=99 and trace these ID.
We typically create merger trees and merger histories using the dark matter particles, which also have unique, immutable IDs. But DM particles are also never created or destroyed, and never change in mass, making this somewhat more clear. The "SubLink" and "LHaloTree" algorithms both do this.
An alternative "SubLink_gal" uses instead the star particles and star-forming gas cells to connect subhalos between snapshots, which could in some cases give different answers. But in general they should be quite similar. (This is not publicly available, but could be provided if it is important to you).
You can certainly follow back stellar particles, using their IDs, to understand e.g. what star particles came from which progenitor/merged galaxies.
What star particles came from which progenitor/merged galaxies is what I need to know. Thank you again!