create a add_extended_source to gunagala

[lspitler]

Perhaps based upon the existing PSF code? It would use the PSF that has been loaded to convolve the extended source & scale it according to the desired brightness.

[lspitler]

Words of wisdom about this Issue from @AnthonyHorton on #mock_images on slack:

Yep. Could be developed outside of it initially, but would certainly want to integrate it once it's working.
Existing gunagala code works fine for creating a noiseless star field image (which is just an astropy.units.Quantity array). Then need to take a galaxy image, scale the pixel values (can use gunagala functions to convert surface brightnesses to electron/s/pixel or overall brightness to electrons/s), add it to the noiseless starfield image, then feed that result into the gunagala function to add noise. (edited)
Can do that stuff in the notebook for now.
That wouldn't end up convolving the galaxy image with the PSF, but I think that's the second step. That aspect really should be done inside gunagala.

[lspitler]

This Issue is not really well-defined, but I think let's leave it open as it might be that we develop a solution that can later be adapted.

[lspitler]

OK, I think will involve starting with the same gunagala code that places individual stars in an image. The only difference is that this new code will place an inputed image (e.g. a simulated galaxy), whereas the existing star code places the PSF (since stars are point sources).

[bazkiaei]

maybe just do this outside of gunagala first