Simulating Image Coaddition with the Nancy Grace Roman Space Telescope: II. Analysis of the Simulated Images and Implications for Weak Lensing

One challenge for applying current weak lensing analysis tools to the NancyGrace Roman Space Telescope is that individual images will be undersampled. Ourcompanion paper presented an initial application of Imcom - an algorithm thatbuilds an optimal mapping from input to output pixels to reconstruct a fullysampled combined image - on the Roman image simulations. In this paper, wemeasure the output noise power spectra, identify the sources of the majorfeatures in the power spectra, and show that simple analytic models that ignoresampling effects underestimate the power spectra of the coadded noise images.We compute the moments of both idealized injected stars and fully simulatedstars in the coadded images, and their 1- and 2-point statistics. We show thatthe idealized injected stars have root-mean-square ellipticity errors (1 - 6) x10-4 per component depending on the band; the correlation functions are >= 2orders of magnitude below requirements, indicating that the image combinationstep itself is using a small fraction of the overall Roman 2nd moment errorbudget, although the 4th moments are larger and warrant further investigation.The stars in the simulated sky images, which include blending and chromaticityeffects, have correlation functions near the requirement level (and below therequirement level in a wide-band image constructed by stacking all 4 filters).We evaluate the noise-induced biases in the ellipticities of injected stars,and explain the resulting trends with an analytical model. We conclude byenumerating the next steps in developing an image coaddition pipeline forRoman.