I'm analyzing TNG300-1 data. I came across with a few primary subhalos, their total dm mass drops over few snapshots for z<1. Stellar mass doesn't vary it's only gas and dm.
I checked there are no major or minor mergers and no evidence on tidal stripping. I was wondering what could be the possible cause other than a resolution issue.
Thank you for your time!
Please see also this discussion.
Loss of gas mass and DM mass is a normal result of stripping - if this is a central subhalo, then was it always a central in the past? If not, it is possibly a backsplash galaxy.
I checked it's a central subhalo for recent redshifts but for some snapshots it's not. Thanks alot
Can a subhalo total dm mass > it's parent halos total dm mass?
When I checked dm mass evolution of the above subhalo(A) , when it's not the primary subhalo I checked the new primary subhalos(B) mass and it's larger than the parent halos mass. And B's position is within 0.7ckpc over all the snapshots so it's still in the same host halo
If you can provide some specific IDs and snapshot numbers (and simulation names), I could help answer better.
A subhalo cannot have a total mass larger than the total mass of its parent halo, because the subhalo is made up of a subset of particles which are, at most, equal to those of its parent halo.
It's TNG300-1. I'm looking at subhalo 1783251(at snapshot 99). But it's not primary subhalo for some snapshots and subhalo 0 becomes primary subhalo(starting from snapshot 98).
What I found was for snapshots <=44, subhalo ido dm mass > it's parent halo dm mass.
Using the SubLink MPB, this subhalo is traced to subhalo 658641 at snapshot 44, with SubhaloMassType = 175.8 and parent GroupMassType = 208.2.
Thanks for your response. You are right but what I had assumed was subhalo 0(at snap 99) belonged to the same parent halo for all the snapshots but which was wrong.
In the plot I have attached (all distance is measured from the parent halo of the 1783251 subhalo at sub 99), I started looking at subhalo 1783251 at snap 99 (orange color :subhalo id0). But it becomes secondary at snap 98 and some other. So I checked the sublink for the new primary subhalo at snap 98 id 0 (blue : subhalo id1) . I'm wonder why sudden primary subhalo change at snapshot 98
Each of the swaps between the blue and orange is due to the "subhalo switching problem". This is an unfortunate reality in the merger trees: whenever two subhalos are close (i.e. merging) and have roughly the same mass, then SubFind cannot really distinguish which of them should be called the "central". So from one snapshot to the next, the choice of the "central" can swap. Because most of the particles in a halo are assigned to a central, this causes spikes in e.g. total mass.
Depending on what you're doing, you can ignore them, or interpolate over them, or handle them in some other reasonable way.