AKARI observation of early-type galaxies in Abell 2218

Ko, J.; Im, M.; Lee, H. M.; Lee, M. G.; Hopwood, R. H.; Serjeant, S.; Smail, I.; Hwang, H. S.; Hwang, N.; Shim, H.; Kim, S. J.; Lee, J. C.; Lim, S.; Seo, H.; Goto, T.; Hanami, H.; Matsuhara, H.; Takagi, T. and Wada, T. (2009). AKARI observation of early-type galaxies in Abell 2218. In: Onaka, Takashi; White, Glenn; Nakagawa, Takao and Yamamura, Issei eds. AKARI, A Light to Illuminate the Misty Universe. Astronomical Society of the Pacific Conference Series, 418. San Francisco, USA: Astronomical Society of the Pacific, pp. 495–498.

URL: http://www.aspbooks.org/a/volumes/article_details?...


We describe the AKARI InfraRed Camera (IRC) imaging observation of early-type galaxies (ETGs) in A2218 at z ≅ 0.175. With the imaging capability at 11 and 15 μm, we investigate mid-infrared (MIR) properties of ETGs in the cluster environment. Among our flux-limited sample of 22 optical red sequence ETGs, we find that more than 50% have MIR-excess emission, and the most likely cause of the MIR excess is the circumstellar dust emission from asymptotic giant branch (AGB) stars. The MIR-excess galaxies reveal a wide spread in N3-S11 (3 and 11 μm) colors, indicative of a significant spread (2–11 Gyr) in the mean ages of stellar populations. They are also preferentially located in the outer region, suggesting the environment dependence of MIR-excess ETGs over an area out to a half virial radius.

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