Weak lensing with the Roman Space Telescope: Challenges and wavelength-dependent systematics
The Nancy Grace Roman Space Telescope High-Latitude Imaging Survey will deliver wide-field, high-resolution near-infrared imaging of roughly a billion galaxies, enabling precise measurements of weak gravitational lensing to probe the growth of cosmic structure. As these measurements become increasingly limited by systematics, accurate modeling of the point-spread function (PSF) is critical for robust shear estimation. In this talk, I will discuss wavelength-dependent systematic effects in the PSF and their impact on weak lensing measurements. One key systematic arises from intrinsic differences between the spectral energy distributions of stars, used to model the PSF, and galaxies, used to measure shear, which lead to chromatic biases that can distort inferred lensing signals. Using realistic image simulations, we show that these biases exceed the mission’s science requirements and present a novel mitigation scheme that applies first-order corrections to the PSF to reduce biases within survey requirements. We also explore how the effectiveness of these corrections depends on survey configuration, and how residual biases propagate into cosmic shear and 3×2-point cosmological analyses. On the instrument side, an additional wavelength-dependent effect arises from refraction within the telescope filters. Chromatic aberrations induced by the filter substrate lead to longitudinal and lateral shifts in the PSF, affecting its size and shape across the field of view. We quantify the magnitude of these effects for Roman and demonstrate how they can be accurately modeled and incorporated into image simulations. Together, these results highlight the importance of controlling wavelength-dependent PSF systematics for robust shear calibration and precision cosmological inference with Roman.
For Zoom information, please contact the seminar coordinators.