Public Data Access Overview / Discussion Forum

Hi TNG teams and other friends,
I wonder what's the difference of the 'SubfindDMDensity' between PartType0,1,4? if they are the same thing?

And does the Density and SubfindDensity in the PartType0 mean rho(x,y,z) (N,3)and rho(r)(N)?
if I try to picture a gas mean density profile with r, is it better to using SubfindDensity than Density?

Thanks in advance.
Yihuan

Hello,

Yes SubfindDMDensity is the same measurement for all particle types. Note that this is a local estimate, so it is valid at the position of that gas/DM/star particle.

All such values, including Density and SubfindDensity, are estimates at the precise Coordinates value (x,y,z) of that cell or particle.

There is no rho(r) data, you would need to compute this by first computing r of cells/particles (from the halo center), then binning.

For gas density, you have two options: use average/median values of PartType0/Density at the r you are interested in, or else sum all PartType0/Masses in a bin, i.e. spherical shell, around r, and then normalize by the volume of that bin.

I got it. Thanks again.

Are 'SubfindDMDensity' and 'SubfindDensity' the same thing?

Hi Yun,

No exactly, the first is "dark matter density" and the second is "total density" (i.e., also including baryons).

But since DM dominates, they are going to be generally quite similar.

Do you mean that "SubfindDensity' contains all kinds of particle types?

That's correct, all particle types = DM + baryons.

So, does that mean I can use "SubfindDensity" and "coordinates" to compute the power spectrum of all matter (DM + baryons) directly?

Hello,

It depends what your goal is, I would read again the description of SubfindDensity carefully. This is a local mass density estimate, at the location of each Coordinates, which is based on an adaptive-size smoothing kernel.

Personally I would not have thought to use it to compute a power spectrum, but instead the combination of Masses and Coordinates which gives the (un-smoothed) mass distribution within the simulation volume.

Thank you for your clarification!