Selection of the main progenitor in the TNG 50 MW/M31 cutouts
Chris Zingler
12h
Hello!
I have a question regarding the selection of the main progenitor and the parameter “InSitu” in the MW/M31 cutout data from TNG50.
According to the documentation of the MW/M31 dataset, the cutouts are “following the position of the main progenitor in time” and “a stellar particle is considered to have been formed in situ if the subhalo in which it was formed lies along the ‘main branch’ of the subhalo in which the stellar particle is currently found.”
However, when working with the data, I stumbled across a few cases where this description does not seem to be consistent with the data.
For example, following the SubLink progenitors of SubhaloID 388544 at snapshot 99 leads to SubhaloID 148320 at snapshot 33. However, when loading the snapshot 33 cutout of SubhaloID 388544 from the MW/M31 dataset, I find that most stellar particles actually have a SubfindID of 148319 rather than 148320, which should be the main progenitor. Moreover, there is only one stellar particle in the snapshot 33 cutout of 388544 with a SubfindID of 148320.
Additionally, when looking at the “InSitu” parameter of this cutout, I find that the particles with SubfindID 148319 are assigned a value of 1, even though they do not originate from the SubLink main progenitor line.
This becomes even more apparent when looking at snapshot 39 of SubhaloID 388544. In this snapshot, roughly half of the stellar particles have a SubfindID of 214684, while the other half have a SubfindID of 214683. Following the SubLink main progenitor of 388544 to snapshot 39 gives SubhaloID 214684. However, “InSitu” is set to 0 for the particles with the SubfindID of the main progenitor, while it is set to 1 for the particles with SubfindID 214683.
Am I interpreting the main progenitor ID incorrectly, or am I using the wrong method to determine the main progenitor altogether?
Hello!
I have a question regarding the selection of the main progenitor and the parameter “InSitu” in the MW/M31 cutout data from TNG50.
According to the documentation of the MW/M31 dataset, the cutouts are “following the position of the main progenitor in time” and “a stellar particle is considered to have been formed in situ if the subhalo in which it was formed lies along the ‘main branch’ of the subhalo in which the stellar particle is currently found.”
However, when working with the data, I stumbled across a few cases where this description does not seem to be consistent with the data.
For example, following the SubLink progenitors of SubhaloID 388544 at snapshot 99 leads to SubhaloID 148320 at snapshot 33. However, when loading the snapshot 33 cutout of SubhaloID 388544 from the MW/M31 dataset, I find that most stellar particles actually have a SubfindID of 148319 rather than 148320, which should be the main progenitor. Moreover, there is only one stellar particle in the snapshot 33 cutout of 388544 with a SubfindID of 148320.
Additionally, when looking at the “InSitu” parameter of this cutout, I find that the particles with SubfindID 148319 are assigned a value of 1, even though they do not originate from the SubLink main progenitor line.
This becomes even more apparent when looking at snapshot 39 of SubhaloID 388544. In this snapshot, roughly half of the stellar particles have a SubfindID of 214684, while the other half have a SubfindID of 214683. Following the SubLink main progenitor of 388544 to snapshot 39 gives SubhaloID 214684. However, “InSitu” is set to 0 for the particles with the SubfindID of the main progenitor, while it is set to 1 for the particles with SubfindID 214683.
Am I interpreting the main progenitor ID incorrectly, or am I using the wrong method to determine the main progenitor altogether?
Thank you very much!