skipped snapshots in merger trees (orbit integration)
Xu Li
5 Sep '23
I read the FirstProgenitorID[0] and NextProgenitorID[1] of the 33 snapNum. but their snapNum is not 32 but 31. So how to definite their merger? Are they merger in 31 or 32, or their merger from 31 to 33?
Dylan Nelson
6 Sep '23
The merger trees can "skip" a snapshot, if it is impossible to identify the link at that snapshot.
In this case, if there is a merger, it occurs between snapshot 31 and 33. But exactly when is not known from this information alone.
This is exactly the same as always. If there had been no skip, then you could have said the merger occurred between snapshots 32 and 33, but not the exact time.
If you want to derive a more exact "merger time", you could e.g. interpolate or integrate the orbits of the galaxies involved.
Xu Li
11 Sep '23
Thanks.
And if I want to integrate the orbits of the galaxies, could I only consider the the galaxies which are going to merger.
Dylan Nelson
11 Sep '23
Yes I would say that, for a merger of 2 systems, considering only those systems would be fine. However, the background dark matter halo potential will be important. If you really want to try this, I would suggest to try to follow the methodology of some other paper that you find taking a similar approach.
I read the FirstProgenitorID[0] and NextProgenitorID[1] of the 33 snapNum. but their snapNum is not 32 but 31. So how to definite their merger? Are they merger in 31 or 32, or their merger from 31 to 33?
The merger trees can "skip" a snapshot, if it is impossible to identify the link at that snapshot.
In this case, if there is a merger, it occurs between snapshot 31 and 33. But exactly when is not known from this information alone.
This is exactly the same as always. If there had been no skip, then you could have said the merger occurred between snapshots 32 and 33, but not the exact time.
If you want to derive a more exact "merger time", you could e.g. interpolate or integrate the orbits of the galaxies involved.
Thanks.
And if I want to integrate the orbits of the galaxies, could I only consider the the galaxies which are going to merger.
Yes I would say that, for a merger of 2 systems, considering only those systems would be fine. However, the background dark matter halo potential will be important. If you really want to try this, I would suggest to try to follow the methodology of some other paper that you find taking a similar approach.
I suggest to look at the recent paper https://arxiv.org/abs/2309.05708 (Section 2.4).