### What are the relationships between different PartTypes, i.e. gas, dm, stars and bh?

Yun Wang
• 19 Aug '20

Hi Dylan and TNG team,

From the TNG-project website, I learned that the simulation box only contains DM particles and gas cells.
So I guess that 'stars' are composed of gas cells and 'Black holes' may be made up of DM particles and gas cells.

Another possibility is that the 'stars' and 'black holes' are completely different particle types from gas cells and DM.

So, which one is true?

Dylan Nelson
• 19 Aug '20

Hi Yun,

Please check the data documentation carefully.

Yun Wang
• 19 Aug '20

Thank you Dylan.
I also have one question.
I found that the field "SubfindDensity" still exists in PartType1, i.e. DM. Does it mean that "SubfindDensity" is the total matter (DM+baryon) comoving mass density at the corresponding coordinate of the DM particle?

Yun Wang
• 20 Aug '20

Hi Dylan,
Sorry for disturbing you again.
If I need the information about the total matter density, i.e. \rho (x, y, z) inside some coordinate range, should I load "SubfindDensity" fields for all PartTypes (0, 1, 4, 5) ?

Dylan Nelson
• 20 Aug '20

Hello Yun,

Please read the definitions of the fields carefully. As we discussed, the SunfindDensity field, for any particle type, gives a local estimate of the total matter density at the position of that particle. These are just samples at the positions of particles. You could also estimate the local matter density at any arbitrary point in space, by using any appropriate interpolation method.

Yun Wang
• 20 Aug '20

Thank you, I see what you mean.

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