Hi,
I am currently working with the TNG100 simulation data. In the particle data (e.g. PartType4), the velocities are in units of km*sqrt(a)/s. Where does the sqrt(a) come from? I would expect either km/s (peculiar velocity) or km*a/s (comoving velocity). If you were to calculate the angular momentum, how would you use the velocity? Would you divide or multiply by sqrt(a) or leave it as is?
Kind regards,
Marloes
Dylan Nelson
6 Dec '23
This is essentially a historical fact, due to how velocities are stored internally in the code. It has been the same since Gadget-2 in 2005. You can see additional details in the Gadget-2 users guide (page 32), and remains the same in AREPO and Gadget-4.
Hi,
I am currently working with the TNG100 simulation data. In the particle data (e.g. PartType4), the velocities are in units of
km*sqrt(a)/s. Where does thesqrt(a)come from? I would expect eitherkm/s(peculiar velocity) orkm*a/s(comoving velocity). If you were to calculate the angular momentum, how would you use the velocity? Would you divide or multiply bysqrt(a)or leave it as is?Kind regards,
Marloes
This is essentially a historical fact, due to how velocities are stored internally in the code. It has been the same since Gadget-2 in 2005. You can see additional details in the Gadget-2 users guide (page 32), and remains the same in AREPO and Gadget-4.