AKARI Observation of the North Ecliptic Pole (NEP) Supercluster at z = 0.087: Mid-infrared View of Transition Galaxies
Abstract
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 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 (1010 M ⊙ < M * < 1010.5 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 * > 1010.5 M ⊙) at any galaxy density. The fraction of the intermediate-MXG among red-sequence galaxies at 1010 M ⊙ < M * < 1011 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2012
- DOI:
- 10.1088/0004-637X/745/2/181
- arXiv:
- arXiv:1111.6693
- Bibcode:
- 2012ApJ...745..181K
- Keywords:
-
- galaxies: clusters: general;
- galaxies: evolution;
- galaxies: stellar content;
- infrared: galaxies;
- surveys;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 46 pages, 25 figures, accepted for publication in ApJ