Simulating Image Coaddition with the Nancy Grace Roman Space Telescope. IV. Hyperparameter Optimization and Experimental Features

Abstract For weak gravitational lensing cosmology with the forthcoming Nancy Grace Roman Space Telescope, image coaddition (or construction of oversampled images from undersampled ones) is a critical step in the image processing pipeline. In the previous papers in this series, we re-implemented the I mcom algorithm, which offers control over point-spread functions (PSFs) in coadded images, and applied it to state-of-the-art image simulations for Roman. In this work, we systematically investigate the impact of I mcom hyperparameters on the quality of measurement results. We re-coadd the same 16 blocks ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.75</mml:mn> <mml:mo>×</mml:mo> <mml:mn>1.75</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">arcmin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> , 2688 × 2688 pixels each) from OpenUniverse2024 simulations with 26 different configurations in each of five bands. We then compare the results in terms of 12 objective evaluation criteria, including internal diagnostics of I mcom , properties of coadded noise frames, measurements of injected point sources, and time consumption. We demonstrate that: (i) the Cholesky kernel is the best-known linear algebra strategy for I mcom , (ii) for our measurements, a wide Gaussian target output PSF outperforms a smoothed Airy disk or a narrow Gaussian, (iii) kernel-specific settings are worth considering for future coaddition, and (iv) I mcom experimental features studied in this work are either inconsequential or detrimental. We end this paper by discussing current and next steps of I mcom -related studies in the context of Roman shear and clustering measurements.