Near-infrared spectroscopy of a massive young stellar object in the direction toward the Galactic Center: XCN and aromatic C-D features

TL;DR

This study uses near-infrared spectroscopy to analyze a massive young stellar object near the Galactic Center, revealing complex ice and gas features, and providing insights into interstellar chemistry and prebiotic molecule formation.

Contribution

It presents detailed spectral analysis of a young stellar object, identifying key features like XCN and aromatic C-D, and explores their implications for interstellar chemistry and deuteration processes.

Findings

Detection of XCN correlated with Br alpha emission.

Identification of aromatic C-D emission linked to PAH deuteration.

Insights into the formation of prebiotic molecules in the ISM.

Abstract

We report near-infrared (2.5--5 micron) long-slit (~ 30 arcsec) spectroscopy of a young stellar object in the direction toward the Galactic center with the Infrared Camera on board the AKARI satellite. The present target is suggested to be AFGL 2006 based on its very red color and close location. The spectra show strong absorption features of H$_2$O and CO$_2$ ices, and emission of HI Br alpha recombination line and the 3.3 micron band, the latter of which originates from polycyclic aromatic hydrocarbons (PAHs) or materials containing PAHs. The spectra show a broad, complex absorption feature at 4.65 micron, which is well explained by a combination of absorption features of CO ice, CO gas, and XCN, and HI Pf beta emission. The spectra also indicate excess emission at 4.4 micron. The characteristics of the spectra suggest that the object is a massive young stellar object. The XCN feature shows a good correlation with the Br alpha emission, suggesting that the photolysis by ultraviolet photons plays an important role in the formation of the XCN carriers, part of which are attributed to OCN$^-$. The 4.4 micron emission shows a good correlation with the 3.3 micron PAH emission, providing supporting evidence that it comes from the aromatic C-D stretching vibration. The formation of OCN$^-$ is of importance for the formation process of prebiotic matter in the interstellar medium (ISM), while the detection of aromatic C-D emission provides valuable information on the deuteration process of PAHs in the ISM and implications on the hiding site of the missing deuterium in the ISM.