voids, filaments

Moritz Haslbauer
  • 26 Feb '18

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.

Dylan Nelson
  • 6 Mar '18

Hi Moritz,

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.

Moritz Haslbauer
  • 7 Mar '18

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.

Dylan Nelson
  • 7 Mar '18

Hi Moritz,

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).

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