[yt-users] Absorption Spectrum from Gadget snapshot problem

Jared Coughlin Jared.W.Coughlin.29 at nd.edu
Thu Aug 20 14:31:12 PDT 2015


Just one final question: what is the gamma parameter that is required by
add_line()? I'm assuming it's the photoionization rate at the redshift in
question.  What units should it be in (I'm assuming s^-1, but I just
thought I'd be sure)?
-Jared

On Thu, Aug 20, 2015 at 2:03 PM, Cameron Hummels <chummels at gmail.com> wrote:

> Hi Jared,
>
> Yes, the setup functions are what you should use to postprocess the
> dataset prior to using the make_spectrum() call.  Essentially, just create
> whatever derived field you choose (in this case H_number_density) using the
> setup function and then make_spectrum() should work ok.
>
> Cameron
>
> On Thu, Aug 20, 2015 at 8:43 AM, Jared Coughlin <
> Jared.W.Coughlin.29 at nd.edu> wrote:
>
>> I do not write the hydrogen number density to the snapshot. I was
>> planning on adding it post-processing. I read about the setup functions,
>> but I don't really understand how they work. I already have a routine in
>> place that gets n_HI from the density and temperature in the snapshot. Are
>> set up functions the tool I should be using?
>> -Jared
>> Hi Jared,
>>
>>
>>>
>>> I have two questions. First: When calling make_light_ray and passing it
>>> fields, do I need to pass it H_number_density? Second: Does yt read in
>>> those fields from the gadget snapshot, or does it calculate them from the
>>> data in the snapshot (for example, a standard gadget snapshot does not
>>> write the temperature, but rather the internal energy)?  Thanks!
>>>
>>
>>
>> When you run sp.add_line(), you're trying to add a line associated with a
>> field, in this case, you're associating it with the "H_number_density"
>> field.  AbsorptionSpectrum expects that field to be present in the light
>> ray (in this case lr.h5) when you run make_spectrum().  The
>> "H_number_density" field is a grid-celled neutral hydrogen number density,
>> which is present in some simulation outputs, however, I do not know if it
>> is automatically populated for the custom gadget dataset on which you're
>> running.  Do you trace the neutral hydrogen in your gadget simulation?  If
>> so, does it spit out to a particle field that you can then deposit into a
>> grid-based field?  Or were you looking to approximate the HI number density
>> in yt  by making some assumptions based on the density, temperature,
>> radiation field, etc.?
>>
>> Cameron
>> --
>> Cameron Hummels
>> NSF Postdoctoral Fellow
>> Department of Astronomy
>> California Institute of Technology
>> http://chummels.org
>>
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>
>
> --
> Cameron Hummels
> NSF Postdoctoral Fellow
> Department of Astronomy
> California Institute of Technology
> http://chummels.org
>
> _______________________________________________
> yt-users mailing list
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>
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