chromatic "RealGalaxy" objects from hydro simulations

Today I heard a talk by Gregory Snyder ( @gsnyder206 ) in which he showed something super cool:
He's been making synthetic galaxy images from the Illustris simulation to simulate data in various passbands. Examples are
http://www.stsci.edu/~gsnyder/hudftool.html

They are working to put these into GalaxyZoo to get morphology classifications, too. So this immediately made me think it would be very interesting to have these in GalSim (apparently @msimet had the same idea when she heard this talk too). The basic idea is:

• Okay, they aren't real galaxies. But they are realistically complicated, which is very interesting for studies of model bias and so on.
• Unlike our current RealGalaxy catalog from COSMOS, they are chromatic.
• Even when we have chromatic RealGalaxy catalogs from AEGIS, those will be based on just two bands and thus involve a bunch of assumptions. So in some sense these fully chromatic ones from Illustris may be "better" (though within the limitations imposed by hydro simulations not making perfectly realistic galaxies).

A few questions:

1. How should we think about the resolution limit of the simulations? Should we be treating that like a PSF of sorts, perhaps a Gaussian of some width? If so, then GalSim can easily be made to take that into account when matching to the target PSF.

2. How is the information from the simulations available? In particular, how is the color and redshift information encoded? GalSim knows how to take images of the surface brightness profile, but for each galaxy there are presumably two other dimensions (wavelength, redshift) and I would like to understand how those are encoded in order to figure out how to get GalSim to use that information.

Anybody have any thoughts about this idea? Agree/disagree about it being worthwhile? @rmjarvis , @jmeyers314 , ...? I am excited about this and could put some time into it over the summer, though I won't complain about sharing the load if there are any volunteers who want to be involved.

No files, tests, or entry points are named. Start by reviewing GalSim's existing RealGalaxy catalog and chromatic handling, then determine how Illustris simulation resolution, wavelength, color, and redshift data would be represented; done requires an agreed scope and implementation plan.