Processing of polycyclic aromatic hydrocarbons in molecular-loop regions near the Galactic center revealed by AKARI

Abstract

We present an AKARI mid-infrared diffuse map of an area of about 4° × 3° near the Galactic center in the 9μm 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 11.3μm. We detected 9μm 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 9μm is suppressed near the foot points of the CO loops. The ratios of the 9μm to the IRAS 100μm brightness show significant depression near such bright regions in CO emission. With AKARI near-infrared 2.5-5μm spectroscopy, we find that the 3.3μm 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. © 2012 Astronomical Society of Japan.