Hello! Would be there a simple way to check whether a galaxy lies within a void or a filament? I have heard about the code DisPerSE, but maybe there would be an easier method to do this with the Illustris simulation.
No one has yet run Disperse, or similar codes, on Illustris. But if you wanted to give it a try, the results would probably be very interesting, and I would be curious how it goes!
If you really want a topological characterization of environment, then you will need such a code.
If you just want a characterization of environment, you can use the group catalog and count nearby things, e.g. the number of halos above log(msun)=12.0 within a radius of 10 Mpc. Any such 'density estimator' will tell you how crowded or quiet the local volume is.
Thank you for your answer. I think such a "density estimator" would be a good approach. Do you know maybe any papers in which such a characterization of the environment was studied? Or do you know some reference values such that I can get a rough idea which values are typical for voids or dense regions? Another idea would be to calculate the density contrast (i.e. the mass density within a sphere divided by the mass density of the total simulated box for a given subhalo mass range). If for a certain region/sphere the density contrast is higher than one, I can conclude that it would be an "overdense" region.
From the simulation perspective, e.g. https://arxiv.org/abs/1002.0844 which uses 3D matter density (not halo/galaxy density).
From the observational perspective, e.g. https://arxiv.org/abs/1003.4747 deriving galaxy based density in cylinders (which we often convert to spheres in the simulations).