[yt-users] Getting error in Worked Example of Halo Analysis

[Chen Jingjing]

Hi Britton,
When I set critical_density=500, does it mean 500 times of the average
density, or 500 times of the critical density?

Thanks,
Jingjing

2015-03-20 4:22 GMT-04:00 Britton Smith <brittonsmith at gmail.com>:

> Hi Reju,
>
> It looks like the version of the notebook you are working from is a little
> out of date as the syntax for some of those callbacks has changed.  Please,
> have a look here for an updated version:
> http://yt-project.org/doc/cookbook/halo_analysis_example.html
> I just ran this myself and confirmed everything to be working.
>
> As for your other questions:
>
> 1) How to find the center of mass of the halos(
>> hc.add_quantity('center_of_mass') is not working )
>>
>
> By default, the halo catalog is storing the center of the halo as
> calculated by the halo finder that you used.  If you reload the halo
> catalog that you produce, the x, y, and z position of each halo are the
> "particle_position_x", "particle_position_y", "particle_position_z"
> fields.  For example, you could do:
> ds = yt.load(your_halo_catalog)
> ad = ds.all_data()
> print ad["particle_position_x"]
>
> Additionally, the halo catalog has a callback called
> "iterative_center_of_mass" which starts from the original center and
> iteratively recalculates the center of mass while reducing the radius of
> the sphere.  I have found this to work very well for calculating halo
> centers.  If you use this callback, it will rewrite the particle_position
> fields to contain the new center for each halo.  To get more information on
> this callback, do the following:
>
> from yt.analysis_modules.halo_analysis.halo_callbacks import *
> help(iterative_center_of_mass)
>
>
>> 2) How to find virial mass (both M_500 and M_200 ) of the halas
>>
>
> You can find these using the virial_quantities callback.  In the example
> you are working from, you can add another field to the virial_quantities
> callback you use and it would calculate the value of that field where the
> overdensity = 200.  For total mass, the field you want is called
> "matter_mass".  To get M_500 instead of M_200, you can call the
> virial_quantities callback again and give the keyword argument
> critical_density=500.
>
> Britton
>
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>


-- 

Jingjing Chen [ chenjj235 at gmail.com ]
Department of Astronomy
Columbia University
550 West 120th Street
New York, New York 10027
Cell Phone: +1(347)5746709
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