More realistic romanisim input catalogs for large simulations

[schlafly]

Presently romanisim makes very simple test input catalogs. In order to test things like source detection more realistically, we should improve the quality of the test data, and therefore the test input catalogs.

One approach would be to take catalog data from a deep field, to randomize it, and to put those sources into romanisim images. COSMOS is a large deep field with many-band data that is likely a good source of data for this kind of project.

The proposal is to generate romanisim tabular input catalogs by

• taking data from COSMOS
• sampling sources from the COSMOS field with the same areal density as in COSMOS
• getting Roman fluxes for those sources by either taking the nearest matching band present in the various COSMOS data sets or by interpolating
• getting source shapes from the COSMOS catalog
• randomizing the positions of the sources and angles of the sources, so that the real COSMOS sources become "random" galaxies in an arbitrary Roman field
• Perturbing the COSMOS fluxes by a small amount---perhaps perturbing the overall fluxes by ~20% and the colors by an additional 5%.
• adding real Gaia sources on top of this catalog. We need to make up fluxes for these sources, too. We should probably just assume that all Roman bands are equal to the Gaia G band for now.