Processing of Polycyclic Aromatic Hydrocarbons in Molecular-Loop Regions near the Galactic Center Revealed by AKARI
Oyabu, Shinki; Onaka, Takashi; Yamagishi, Mitsuyoshi; Kaneda, Hidehiro; Kawamura, Akiko; Fukui, Yasuo; Ishihara, Daisuke; Torii, Kazufumi; Kondo, Toru; Mouri, Akio
Japan
Abstract
We present an AKARI mid-infrared diffuse map of an area of about 4° × 3° near the Galactic center in the 9 μm band. The band intensity is mostly attributed to aromatic hydrocarbon infrared emissions of carbonaceous grains at wavelengths of 6.2, 7,7, 8.6, and 11.3 μm. We detected 9 μm emission structures extending from the Galactic plane up to a latitude of ∼ 2°.5, which have spatial correspondence to molecular loops revealed by NANTEN 12CO (J = 1-0) observations. We have found that the surface brightness at 9 μm is suppressed near the foot points of the CO loops. The ratios of the 9 μm to the IRAS 100 μm brightness show significant depression near such bright regions in CO emission. With AKARI near-infrared 2.5-5 μm spectroscopy, we find that the 3.3 μm aromatic hydrocarbon emission is absent in the region associated with the loop, suggesting the processing and destruction of carbonaceous grains in the CO molecular loops.