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

TL;DR

SPHEREx's infrared spectral maps reveal detailed distributions of interstellar ices and PAHs across large nebula regions, providing insights into molecular cloud chemistry and physical conditions.

Contribution

This work presents the first large-scale near-infrared spectral maps of interstellar ices and PAHs, demonstrating the capabilities of SPHEREx for interstellar medium studies.

Findings

Detection of H₂O, CO₂, and CO ice features over large areas

Correlation between PAH emission and other infrared features

Variation in ice feature strength indicating diverse physical conditions

Abstract

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 $\mu$m H$_2$O, 4.27 $\mu$m CO$_2$, and 4.67 $\mu$m CO lines and the 3.28 $\mu$m PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H$_2$O and CO$_2$ 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 H$_2$O and CO$_2$ features varies among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 $\mu$m PAH emission correlates with the emission from the 7.7 and 11.2 $\mu$m 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.