Tracing the Missing Sulfur and Deuterium: The Role of Modified PAHs in the Interstellar Medium

Charles Mentzer^1,2*, Aigen Li², X. J. Yang^3,2

¹Institute of Astronomy, National Tsing Hua University, Hsinchu, Taiwan
²Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA
³Hunan Key Laboratory for Stellar and Interstellar Physics and School of Physics and Optoelectronics, Xiangtan University, Hunan, China

* Presenter:Charles Mentzer, email:cmentzer@gapp.nthu.edu.tw

The interstellar medium (ISM) shows significant depletions of both deuterium and sulfur relative to their expected cosmic abundances, implying that a substantial fraction of these elements may be locked in some sorts of reservoirs. Polycyclic aromatic hydrocarbons (PAHs), a major component of interstellar carbonaceous materials, represent a promising sink for these missing elements through chemical substitution. In this study, we investigate the potential role of sulfurated and deuterated PAHs as reservoirs of the missing interstellar sulfur and deuterium. Here we examine how sulfur incorporation and deuterium enrichment modify the infrared spectral characteristics of PAHs and compare these predictions with Spitzer and JWST observations of which such features may have been previously overlooked. Our results strengthen the case that sulfurated and deuterated PAHs could constitute a hidden reservoir of sulfur and deuterium in the ISM, providing a molecular-scale explanation for their observed elemental depletions across diverse galactic environments.

Keywords: PAH, ISM, Deuterium, Sulfur