For kinematics of galaxies how we can figure out the velocity map in TNG for gas or stars?
I'll be grateful for your help .
If you would like some images or examples, you can use the Visualize Galaxies and Halos tool. Select "gas" or "stars" as the particle type, and vel_los as the field.
If you select edge-on rotation, and set the image size to e.g. 5.0 in units of rHalfMassStars, you should see the typical red-blue signature of a rotating disk, for most intermediate mass halos. Fig 6 of the data release paper shows an example of this.
If you would like to compute such maps, the easiest way is to adopt the x-y axes as the image plane, projecting along the z direction. Then the "line of sight velocity" is simply Velocities and you can create an image, or other analysis, from this (gas cell/star particle) field.
Thank you very much for your help.