[yt-users] questions about halo profiling

[Irina Dvorkin]

Hi Britton,

Thanks for the clarifications!

Irina

Quoting "Britton Smith" <brittonsmith at gmail.com>:

> 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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>