- Ko, J
- Im, M
- Lee, HM
- Lee, MG
- Kim, SJ
- Shim, H
- Jeon, Y
- Hwang, HS
- Willmer, CNA
- Malkan, MA
- Papovich, C
- Weiner, BJ
- Matsuhara, H
- Oyabu, S
- Takagi, T
- et al.
We present the mid-infrared (MIR) properties of galaxies within a supercluster in the north ecliptic pole region at z ∼ 0.087 observed with the AKARI satellite. We use data from the AKARI NEP-Wide (5.4deg ) IR survey and the CLusters of galaxies EVoLution studies (CLEVL) mission program. We show that near-IR (3 μm)-mid-IR (11 μm) color can be used as an indicator of the specific star formation rate and the presence of intermediate-age stellar populations. From the MIR observations, we find that red-sequence galaxies consist not only of passively evolving red early-type galaxies, but also of (1) "weak-SFGs" (disk-dominated star-forming galaxies that have star formation rates lower by ∼4 × than blue-cloud galaxies) and (2) "intermediate-MXGs" (bulge-dominated galaxies showing stronger MIR dust emission than normal red early-type galaxies). These two populations can be a set of transition galaxies from blue, star-forming, late-type galaxies evolving into red, quiescent, early-type ones. We find that the weak-SFGs are predominant at intermediate masses (10 M < M < 10 M ) and are typically found in local densities similar to the outskirts of galaxy clusters. As much as 40% of the supercluster member galaxies in this mass range can be classified as weak-SFGs, but their proportion decreases to <10% at larger masses (M > 10 M ) at any galaxy density. The fraction of the intermediate-MXG among red-sequence galaxies at 10 M < M < 10 M also decreases as the density and mass increase. In particular, ∼42% of the red-sequence galaxies with early-type morphologies are classified as intermediate-MXGs at intermediate densities. These results suggest that the star formation activity is strongly dependent on the stellar mass, but that the morphological transformation is mainly controlled by the environment. © 2012. The American Astronomical Society. All rights reserved. 2 10 10.5 10.5 10 11 ⊙ * ⊙ * ⊙ ⊙ * ⊙