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AKARI observation of early-type galaxies in Abell 2218

By J. Ko, M. Im, H. M. Lee, M. G. Lee, R. H. Hopwood, S. Serjeant, I. Smail, H. S. Hwang, N. Hwang, H. Shim, S. J. Kim, J. C. Lee, S. Lim, H. Seo, T. Goto, H. Hanami, H. Matsuhara, T. Takagi and T. Wada


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

Publisher: Astronomical Society of the Pacific
Year: 2009
OAI identifier:
Provided by: Open Research Online

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