When visualising the dark matter mass of a halo, say a 10^13 M_sol halo between 0.1 < z < 0.5 across a FOV of 6 arcsec, I notice their seems to be a lot of clumpiness. I thought is might be the subhalos, but I mapped their positions to the image and they didn't line up with the clumps. I was just wondering if this small scale structure is physical or if it's a resolution effect?
Perhaps you can provide a specific example? It is either (i) resolved substructure, or (ii) individual DM particles i.e. representing discreteness of the N-body approach (the resolution limit of the simulation).
Here's an example. I suspect it may be the latter given that within the field of view there should only be a handful of subhalos, but I just wanted to make sure.
Yes it is certainly particle discreteness. You see the scalebar of 1 ckpc, and TNG50-1 has a gravitational force softening for DM of 0.29 ckpc, which you can think of as a characteristic resolution.