Spectral Response of SPHEREx

May 2026 • 2026ApJS..284...10H

Authors • Hui, Howard • Bock, James J. • Condon, Samuel • Dowell, C. Darren • Jeong, Woong-Seob • Jo, Young-soo • Korngut, Phil M. • Manatt, Kenneth • Nguyen, Chi • Nguyen, Hien • Padin, Stephen • Park, Sung-Joon • Pyo, Jeonghyun • Yang, Yujin • Ashby, Matthew L. N. • Bach, Yoonsoo P. • Chang, Tzu-Ching • Cheng, Yun-Ting • Chiang, Yi-Kuan • Cooray, Asantha • Crill, Brendan P. • Cukierman, Ari J. • Doré, Olivier • Faisst, Andreas L. • Hora, Joseph L. • Kang, Jae Hwan • Lee, BoMee • Lisse, Carey M. • Masters, Daniel C. • Paladini, Roberta • Rustamkulov, Zafar • Tolls, Volker • Werner, Michael W. • Zemcov, Michael

Abstract • The Spectro Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) is conducting the first all-sky near-infrared spectral survey spanning 0.75─5.0 μm with resolving power R ≍ 35─130. Linear variable filters mounted in front of six H2RG detectors produce a position-dependent spectral response across the focal plane. This paper presents the ground-based spectral calibration of SPHEREx, including the cryogenic apparatus, optical configuration, measurement strategy, analysis pipeline, and resulting calibration products. Monochromatic wavelength scans are used to derive the spectral response function, band center, and resolving power for every pixel. Band centers are measured to better than 1 nm for Bands 1 through 4 (0.75─3.82 μm) and better than 10 nm for Bands 5 and 6 (3.82─5.0 μm). Out-of-band leakage is negligible for detectors above 1.64 μm and is present at the percent level below this wavelength. The resolving power is measured to within 5% and agrees with design expectations to within 10%. An on-sky spectrum of the Cat's Eye Nebula (NGC 6543) constructed from repeated observations provides in-flight verification and shows agreement between ground-calibrated response and astrophysical emission features. Calibration products, including per-pixel band center and resolving power maps, are released through IPAC to support community use of SPHEREx data. The absolute spectral calibration will continue to improve through in-flight measurements, with further reductions in uncertainty expected for the longest-wavelength bands.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-4365/ae522c/pdf
• ELECTR https://doi.org/10.3847/1538-4365/ae522c