SPHEREx Wide-Field Infrared Spectral Mapping of Interstellar Ices and Polycyclic Aromatic Hydrocarbons

We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions.

The maps emphasize the strongest features arising from the 3 μm H₂O, 4.27 μm CO₂, and 4.67 μm CO lines and the 3.28 μm PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions.

The ice absorption maps of H₂O and CO₂ in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas.

The relative strength of the H₂O and CO₂ features varies among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 μm PAH emission correlates with the emission from the 7.7 and 11.2 μm features, but shows small differences that may trace the grain size distribution and variations in the ambient UV field.

SPHEREx all-sky spectral imaging, of which only a small fraction is showcased in this work, will support numerous science investigations including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.

Joseph L. Hora, Jinyoung K. Noh, Gary J. Melnick, Brandon S. Hensley, Roberta Paladini, Jeong-Eun Lee, Matthew L. N. Ashby, Volker Tolls, Jaeyeong Kim, Michael W. Werner, James J. Bock, Sean Bruton, Shuang-Shuang Chen, Tzu-Ching Chang, Yi-Kuan Chiang, Asantha Cooray, Brendan P. Crill, Ari J. Cukierman, Olivier Doré, Andreas L. Faisst, Zhaoyu Huai, Howard Hui, Woong-Seob Jeong, Miju Kang, Phil M. Korngut, Ho-Gyu Lee, Carey M. Lisse, Daniel C. Masters, Giulia Murgia, Chi H. Nguyen, Zafar Rustamkulov, Ji Yeon Seok, Robin Y. Wen, Yujin Yang, Michael Zemcov

Comments: 23 pages, 13 figures, 1 table. Accepted to the Astrophysical Journal March 11, 2026
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2603.12390 [astro-ph.GA] (or arXiv:2603.12390v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2603.12390
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Submission history
From: Joseph L. Hora
[v1] Thu, 12 Mar 2026 19:09:48 UTC (33,148 KB)
https://arxiv.org/abs/2603.12390
Astrobiology, Astrochemistry,