Detection of the unidentified infrared bands in a filament of the dwarf galaxy NGC1569

Abstract

We made near- to mid-infrared imaging and spectroscopic observations of the dwarf galaxy NGC 1569 with the Infrared Camera (IRC) on board AKARI. The unidentified infrared (UIR) band features at 6.2, 7.7, and 11.2 μm, which are generally attributed to polycyclic aromatic hydrocarbons (PAHs), are clearly detected in a structure associated with an H filament. The filament is filled with X-ray emission and is thought to be formed by outflow from the galaxy. Since PAHs are destroyed rapidly in hot plasma, it is most likely that PAHs in the filament are produced from fragmentation of large carbonaceous grains in the shock. We also detect excess emission in 2-5 μm in the filament, which may come from very small grains. © 2008 International Astronomical Union.