Far-infrared Emission from the Intergalactic Medium in Stephan's Quintet Revealed by AKARI

Stephan's Quintet (SQ, HCG92) was observed with the Far-Infrared Surveyor on board AKARI in four far-infrared (IR) bands at 65, 90, 140, and 160 μm. The AKARI four-band images show far-IR emission in the intergalactic medium of SQ. In particular, the 160 μm band image shows single peak emission in addition to the structure extending in the north-south direction along the shock ridge as seen in the 140 μm band, H₂ emission, and X-ray emission. Whereas most of the far-IR emission in the shocked region comes from the cold dust component, shock-powered [C II]158 μm emission can significantly contribute to the emission in the 160 μm band that shows a single peak at the shocked region. In the shocked region, the observed gas-to-dust mass ratio is in agreement with the Galactic one. The color temperature of the cold dust component (~20 K) is lower than that in surrounding galaxies (~30 K). We discuss a possible origin of the intergalactic dust emission.