Softening lengths

Peter Lustig
  • 27 Apr '21


I have a question about the softening lengths. Using the api to access the data I find for example for TNG100-1

softening_dm_comoving = 1.0
softening_stars_comoving = 1.0.

On the other hand I find in Nelson et al. 2018:
"the first simulation, TNG100 … the gravitational softening length of the dark matter and stars is 0.7 kpc at z=0, and the gas component has an adaptive softening with a minimum of 185 comoving parsecs…."

Sorry if I am missing an obvious point here but could you please help me understanding how these numbers relate to each other? What is the minimum comoving softening length and how can I get the softening length in physical units as a function of redshift?
And is the softening length for stellar particles the same as for gas particles?

Thanks a lot in advance,

Dylan Nelson
  • 27 Apr '21

Hi Peter,

The values

softening_dm_comoving = 1.0
softening_stars_comoving = 1.0

are in "code length units" of ckpc/h. So dividing by h gives 0.7 ckpc, or 0.7 pkpc at z=0.

Stars and DM have similar softenings, while for gas it is quite different (adaptive). This should be well described in Pillepich+ (2018).

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