Jongwan Ko, Myungshin Im, Hyung Mok Lee, Myung Gyoon Lee, Seong Jin Kim, Hyunjin Shim, Yiseul Jeon, Ho Seong Hwang, Christopher N. A. Willmer, Matthew A. Malkan, Casey Papovich, Benjamin J. Weiner, Hideo Matsuhara, Shinki Oyabu, Toshinobu Takagi
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 (5.4 deg2) IR survey and
the CLusters of galaxies EVoLution studies (CLEVL) mission program. We show
that near-IR (3 {\mu}m)-mid- IR (11 {\mu}m) 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-SFG" (disk-dominated star-forming galaxies which have star
formation rates lower by \sim 4 \times than blue-cloud galaxies), and 2)
"intermediate- MXG" (bulge-dominated galaxies showing stronger MIR dust
emission than normal red early-type galaxies). Those 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-SFG are predominant
at intermediate masses (1010M\odot < M\star < 1010.5M\odot) 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\star
> 1010.5 M\odot) at any galaxy density. The fraction of the intermediate-MXG
among red- sequence galaxies at 1010M\odot < M\star < 1011M\odot also decreases
as the density and mass increase. In particular, \sim42% of the red-sequence
galaxies with early-type morphologies are classified as intermediate-MXG 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.
View original:
http://arxiv.org/abs/1111.6693
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