OBSERVATIONS OF STAR FORMATION INDUCED BY GALAXY-GALAXY AND GALAXY-INTERGALACTIC MEDIUM INTERACTIONS WITH AKARI

Abstract

Nearby spiral galaxies M101 and M81 are considered to have undergone a galaxy-galaxy interaction. M101 has experienced HI gas infall due to the interaction. With AKARI far-infrared (IR) photometric observations, we found regions with enhanced star forming activity, which are spatially close to regions affected by the interaction. In addition, the relation between the star formation rate (SFR) and the gas content for such regions shows a significant difference from typical spiral arm regions. We discuss possible explanations for star formation processes on a kiloparsec scale and the association with interaction-triggered star formation. We also observed the compact group of galaxies Stephan’s Quintet (SQ) with the AKARI Far-infrared Surveyor (FIS). The SQ shows diffuse intergalactic medium (IGM) due to multiple collisions between the member galaxies and the IGM. The intruder galaxy NGC 7318b is currently colliding with the IGM and causes a large-scale shock. The 160 micron image clearly shows the structure along the shock ridge as seen in warm molecular hydrogen line emission and X-ray emission. The far-IR emission from the shocked region comes from the luminous [CII]158 ㎛ line and cold dust (~20 K) that coexist with molecular hydrogen gas. Survival of dust grains is indispensable to form molecular hydrogen gas within the collision age (~5 Myr). At the stage of the dusty IGM environment, [CII] and H₂ lines rather than X-ray emission are powerful cooling channels to release the collision energy.