Dear TNG Team,
I am in doubt about the size of radial bins when computing azimuthally averaged subhalo stellar mass profiles. Can I trust the values estimated for a radial bin where its width is equal to the softening length or even smaller?
Thank you for the platform and data!
The answer really depends on the application/scientific question. For stars and dark matter, the gravitational softening length is a good benchmark length-scale, although the scale below which the results become unreliable could be a factor of a few in either direction, depending on your use. A generally good approach is to repeat any profile-type analysis on the resolution series, i.e. if you are analyzing TNG100-1, then repeat for TNG100-2 and TNG100-3 (e.g. at fixed halo mass). By doing so you will get an excellent idea of how behavior at small radii depends on numerical resolution, and it will likely be easy to identify the "resolution length scale" of interest. For a concrete example, I refer you to Pillepich+2018 Fig A2. Note that for the gas the answer may differ, and may be much smaller scales, as the gravitational softening for gas is adaptive down to small values, while the "gas resolution" i.e. physical size of gas cells can be yet smaller still, particularly in the centers of galaxies/halos.