Back to Volume
Paper: Unidentified Infrared Bands Associated with Extended Structures of Galaxies Based on AKARI Observations
Volume: 414, Cosmic Dust—Near and Far
Page: 227
Authors: Onaka, T.Kaneda, H.Sakon, I.; Matsumoto, H.
Abstract: Observations with the infrared camera (IRC) on board AKARI clearly reveal the presence of the unidentified infrared (UIR) band emission in the various extended structures of sample galaxies. The presence of the UIR band emission is indicated in diffuse emission surrounding the nearby starburst galaxy M82. The band emission is seen at regions much farther away (several kpc) from the galaxy disk than the Hα emission produced by the superwind of M82. An anti-correlation of the UIR band emission with the X-ray emission is suggested, which may be interpreted in terms of the destruction of the UIR band carriers in hot plasma gas. In the dwarf galaxy NGC1569, the presence of the UIR bands is suggested in an Hα filament by imaging observations and confirmed by subsequent spectroscopic observations with the IRC. The UIR band spectrum of the filament suggests weak 6.2 and 7.7 μm band emission relative to the 11.3 μm band compared to the spectrum of the disk of NGC1569. Much weaker 6.2 and 7.7 μm band emission is seen in elliptical galaxies, suggesting that the different band appearance is related to processing in particular physical conditions in the interstellar medium. The filament of NGC1569 is associated with X-ray emission and is thought to be produced by an outflow triggered by recent star-formation activity. IRC observations further indicate the presence of the UIR band emission in extended structures, which may have been created by a merging event, of the peculiar galaxy NGC2782. The estimated short life time in these violent events suggests that the band carriers in these extended structures are formed from fragmentation of large carbonaceous grains in shocks associated with the outflow or merging event rather than being supplied from stellar sources. AKARI observations suggest that the UIR bands are commonly associated with filamentary structures in galaxies, providing key information on the origin of and the life time of the band carriers.
Back to Volume