[Yt-dev] Simulated Observations: Request for Corrections

[Matthew Turk]

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