Chromatic effects on the PSF and shear measurement for the Roman Space Telescope High-Latitude Wide Area Survey

Journal Article · Wed Jul 30 00:00:00 EDT 2025 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/staf1255· OSTI ID:2587345

Berlfein, Federico ^[1]; Mandelbaum, Rachel ^[1]; Li, Xiangchong ^[2]; Zhang, Tianqing ^[3]; Dodelson, Scott ^[4]; Markovic, Katarina ^[5]

---

1. Carnegie Mellon Univ., Pittsburgh, PA (United States)
2. Carnegie Mellon Univ., Pittsburgh, PA (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)
3. Univ. of Pittsburgh, PA (United States)
4. Carnegie Mellon Univ., Pittsburgh, PA (United States); Univ. of Chicago, IL (United States); Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
5. California Institute of Technology (CalTech), Pasadena, CA (United States)

Weak gravitational lensing (WL) is a key cosmological probe that requires precise measurement of galaxy images to infer shape distortions, or shear, and constrain cosmology. Accurate estimation of the point spread function (PSF) is crucial for shear measurement, but the wavelength dependence of the PSF introduces chromatic biases that can systematically impact shear inference. We focus on biases arising from spectral energy distribution (SED) differences between stars, used for PSF modelling, and galaxies, used for shear measurement. We investigate these effects in Roman’s four design reference mission WL bands (Y106, J129, H158, F184) and wide filter (W146). Using Roman-like image simulations, we quantify the induced shear biases and compare them to requirements on those biases. Multiplicative biases over all galaxies hover around ~0.2 per cent in the WL bands and 2 per cent in the wide filter, exceeding the mission requirement of |m| < 0.032 per cent and relaxed requirement of |m| < 0.1 per cent⁠. In individual redshift bins, biases can reach 0.4–0.9 per cent for the WL bands and 3–6 per cent for the wide filter. Additive biases remain acceptable in the WL bands but exceed systematic limits in the wide filter. We develop and test PSF-level corrections, showing that a first-order correction reduces biases within survey requirements for the WL bands; however, higher-order terms are necessary for the wide filter. Our results highlight the necessity of chromatic corrections for precision WL with Roman and provide a framework for mitigating these biases. Finally, we compare analytical colour-based corrections to self-organizing maps and find that both methods effectively reduce biases.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States); Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: 89243024CSC000002; SC0012704
• OSTI ID: 2587345
• Alternate ID(s): OSTI ID: 2568603
• Report Number(s): BNL--228844-2025-JAAM; FERMILAB-PUB--25-0310-PPD; oai:inspirehep.net:2917282; arXiv:2505.00093
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 542; ISSN 0035-8711; ISSN 1365-2966
• Publisher: Oxford University Press (OUP)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
cosmology: observations
gravitational lensing: weak
techniques: image processing