I have been analysing the gas in subhalos in TNG50,TNG100 (using for example SubhaloMassInHalfRadType) and I noticed some have gas masses of exactly zero. Being Arepo a grid code, is this because the values are extremely low and are rounded to 0., or are calculated using the bound gaseous material, which is 0.?
Thank you for your time,
All gas cells in these simulations have roughly the same mass (they are maintained within a factor of +/- 2, approximately).
So the reason is the second: the mass of a subhalo for a given particle/cell type is the sum of the masses of all particles/cells of that type which are members of that subhalo. If Subfind determines that no gas belongs (i.e. is gravitationally bound) to a subhalo, then its gas mass will be zero.
Wonderful, thank you!