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Hi!
I need to check the mass fraction of winds particles that have positive binding energy. I encountered a problem that the gravitational potential is global, and the total energy is not $E=K+\phi$. There should be an offset $c$ of the gravitational potential. So how can I get the offset C?

Perhaps easiest is to use the (existing) results of Subfind. Since subhalos are defined as gravitationally bound collections of particles/cells, perhaps you can directly look if the wind is inside a subhalo (or not). If any wind are not inside (any) subhalo, they are unbound.

Hi, I still have some questions about what does it mean that "inside" a subhalo. Does it means that the distance of a certain particle is larger than $r_{200}$?

No, it is independent of distance.

Subhalo membership is defined as satisfying the Subfind criteria.

You can find the particles that belong to a given subhalo by either (i) using the subhalo-specific load functions, or (ii) using the offset files, that tell you the ranges of particle indices (of a given type) in the snapshot, that belong to each subhalo.

To provide more information, I loaded the wind particles by il.snapshot.loadSubhalo(basePath, snapNum, subhaloID, 'stars', ['Coordinates', 'Masses', 'Velocities', 'Potential', 'GFM_StellarFormationTime']) and select the "stars" particles with negative 'GFM_StellarFormationTime'. Then, I speculate that the wind particles with negative binding energy will escape the subhalo afterwards. I calculate the mass loss rate by using the mass of wind particle with negative binding energy / escape time, the escape time is defined as the time needs for the wind particle to travel beyond r200.

It seems that I adopted a complex but appropriate method.

I think you should keep in mind that "wind particles" are a temporary phase, which occurs quite close to a star-forming galaxy.

I would not imagine a wind particle ever stays a wind particle, as opposed to recoupling into the gas, all the way out to r200.

Thus if what you are interested in calculating are outflow rates or mass loss rates of gas, from halos, you should also (mainly) consider gas.

Many thanks! Sorry for the typo of my previous comment, it is not "It seems that I adopted a complex but appropriate method.", it is "It seems that I adopted a complex but inappropriate method."

Just to make for I understand it correctly, we may as well not focus too much on the wind particles and should pay more attention to the gas particles when calculating the outflow rate.

Yes that's definitely true, even closer to the galaxy, but definitely at r200.

If you compute the mass fraction in wind particles vs (outflowing) gas at any radius, you can get a sense of how (unimportant) wind particles are.