Centre of mass "CM" versus position of most-bound particle "pos" difference
Jenny Wagner
10 Mar
In the Illustris-3 snapshots, the centre of mass positions as well as the positions of the most bound particle for each halo and subhalo are available.
Questions:
a) what does the difference between the two quantities tell about the symmetry of the halo/subhalo?
b) when should I use the CM as positions for the halo/subhalos and when the position of the most-bound particle? For instance, which positions should I use if I am interested in the radial infall velocities of the subhalos onto the main halo centre?
Thanks in advance!
Dylan Nelson
10 Mar
The distance between these two values is a common definition of relaxedness, in fact. If they are very close, the halo is relaxed.
You should almost always use the position of the most bound particle, as it will be directly in the middle of the most massive galaxy.
The CM can easily be dragged far away, i.e. into the middle of nowhere, for example during an equal mass major merger.
Jenny Wagner
10 Mar
Thanks for the details. Okay, then it looks that I am more interested in the CM with my kinematics questions...
In the Illustris-3 snapshots, the centre of mass positions as well as the positions of the most bound particle for each halo and subhalo are available.
Questions:
a) what does the difference between the two quantities tell about the symmetry of the halo/subhalo?
b) when should I use the CM as positions for the halo/subhalos and when the position of the most-bound particle? For instance, which positions should I use if I am interested in the radial infall velocities of the subhalos onto the main halo centre?
Thanks in advance!
The distance between these two values is a common definition of relaxedness, in fact. If they are very close, the halo is relaxed.
You should almost always use the position of the most bound particle, as it will be directly in the middle of the most massive galaxy.
The CM can easily be dragged far away, i.e. into the middle of nowhere, for example during an equal mass major merger.
Thanks for the details. Okay, then it looks that I am more interested in the CM with my kinematics questions...