### Potential profile

Jinning Liang
• 17 Aug '22

Hi TNG team,

I would like to know the stellar gravitational potential in a galaxy at any coordinate, which is potential profile. Is there any easy way to get it? I can calculate with all stellar particles by -GM/r, but it is very time-consuming for computer. Besides, we have to set a zero point of the potential. How to set zero point in TNG?

Best wishes,
Jinning

Dylan Nelson
• 18 Aug '22

A value of the gravitational potential is available in the Potential field for snapshots, but this (i) includes all matter, not just stars, and (ii) is a global potential, not a galaxy or halo local value.

If you want just stars, you need to calculate this yourself, as you say.

As for zero point, I would think that most likely you are interested in relative potential differences?

Jinning Liang
• 19 Aug '22

Hi Dylan,

Actually I am figuring out how to calculate j_circ(E). I need to find a radius, where \Phi(r)+0.5*v_c^2(r)=E. For v_c, I can calculate it from \sqrt(GM(<r)/r), like what we did to get rotation curves. For \Phi, maybe we should estimate the potential profile. Or is there more easier and more standard way to calculate it?

Dylan Nelson
• 19 Aug '22

Yes Phi is the gravitational potential. I think you can ask Ling, or Shy, for details about how to calculate j_circ(E). You could compare your results to existing results under the "stellar circularities" catalog.

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