[Yt-dev] Simulated Observations: Request for Corrections

John Wise jwise at astro.princeton.edu
Tue Mar 1 07:38:54 PST 2011


Hi Matt,

This is great that you sketched out the plan to make simulated observations through yt.  I think another addition would be 21cm maps.  I implemented these in enzo's projection tool (version 2), but I can add these to yt soon.

Also, we can probably put some pre-defined PSFs for various telescopes / detectors when the user wants to make an image.  Conversions from physical scales to angles would be handy as well, i.e. making a 1 arcmin^2 image.

John

On 1 Mar 2011, at 10:08, Eric Hallman wrote:

> Matt,
>  if we're being generous, we can include the capability to make SZ Compton y maps.  Also Kinematic SZ.  I think those are fields in yt now are they not (SZY and SZ_Kinetic)? Or are those user-derived fields not in public yt?
> 
> cheers,
> 
> On Mar 1, 2011, at 10:02 AM, Matthew Turk wrote:
> 
>> Hi all,
>> 
>> I've been taking stock of where we are for simulated observations, and
>> I wanted to run this past everyone to make sure I'm not missing
>> anything.  I think we have four mechanisms for generating something
>> that could *generously* be called a "Simulated Observation," but for
>> each approach there are caveats.  If someone has something to add, in
>> terms of capability or caveats, I would be eager to hear.  I have not
>> included any methods for generating spectra from galaxies, but I
>> believe this may have been done using the second method below.
>> 
>> = X-ray Observations =
>> 
>> Under the assumption of optically thin gas, projections can be made
>> using emissivity to generated simulated observations.  yt includes a
>> method for handling output from CLOUDY in the ROCO (Smith et al 2008)
>> format, and generating integrated emissivity over given energy ranges.
>> 
>> Caveats: The ROCO format for input requires some non-trivial handling
>> of CLOUDY output.
>> 
>> = SED Generation and Deposition =
>> 
>> Using BC03 models for stellar population synthesis, star particles in
>> a given calculation can be assigned an integrated flux for a specific
>> bandpass.  These fluxes can then be combined using either projections
>> or volume rendering.  This can use CIC interpolation to deposit a
>> total flux into each cell (which should be flux-conserving, modulo a
>> multiplicative factor not currently included) which is then either
>> projected or volume rendered.
>> 
>> Caveats: The deposition method produces far too washed out and murky
>> results.  The multiplicative factor is not currently set correctly
>> universally.
>> 
>> = Thermal Gas Emission =
>> 
>> Applying a black body spectrum to the thermal content of the gas, we
>> can volume render the domain and apply absorption based on broad
>> arguments of scattering.  One could theoretically include star
>> particles as point sources in this, using recent changes to the volume
>> renderer.
>> 
>> Caveats: Scattering that results in re-emission is completely
>> neglected, such as Halpha emission.  Scattering that results in just
>> attenuating the emission is set in an ad hoc fashion.  Emission from
>> point sources, if included at all, is included in a non-conservative
>> fashion.
>> 
>> = Export to Sunrise =
>> 
>> Data can be exported to Sunrise for simulated observation generation.
>> 
>> Caveats: This process is poorly documented.
>> 
>> 
>> 
>> Does that all sound about right?  Does anybody have any additions or
>> corrections to this?
>> 
>> Thanks,
>> 
>> Matt
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> 
> Eric Hallman
> Google Voice: (774) 469-0278
> hallman13 at gmail.com
> 
> 
> 
> 
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