[yt-users] questions about halo profiling

[Britton Smith]

Hi Irina,

You are correct about the way the halo profiler operates, in that it
calculates the density in spherical shells.

With regard to the use of overdensity, you are correct that the definition
used in the halo profiler is with respect to the mean matter density and not
the critical density.  There are many examples in the literature of both
definitions of overdensity (with repect to critical or mean density) so the
choice is somewhat arbitrary.  I agree that there should be explicit note of
this in the documentation.  I will add one.

Britton

On Sat, Aug 14, 2010 at 1:44 PM, Irina Dvorkin <irina at wise.tau.ac.il> wrote:

> Hello All,
>
> After reading the halo profiler python files, I got the impression that it
> reads the position of the halo center and then approximates the halo to a
> sphere with this center, and so includes some mass that is actually not in
> the halo (for example if the halo is an ellipsoid). My knowledge of python,
> however, is rather poor, so it would help me a lot if you could tell me
> whether my understanding is correct.
>
> Also, I noticed that both the halo profiler and the halo finder use a
> non-standard definition of the virial radius: usually it is defined as the
> radius that encompasses a region that is, say, 200 (or other number) times
> denser than the *critical* density at that redshift. The definition in the
> halo profiler is 200 (or other number) times the density of *matter*. So I
> would suggest to specifically mention this definition in the manual because
> it can cause confusion.
>
> Thanks,
> Irina
>
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