1. 1 The mid-infrared view of red-sequence galaxies Jongwan Ko Yonsei Univ. Observatory/KASI Feb. 28, 2012 The Second AKARI Conference: Legacy of AKARI: A Panoramic View of the Dusty Universe

2. 2 Introduction Galaxy colors: bimodal Galaxy colors: bimodal red : little SF and early-type blue : active SF and late-type Optical red-sequence:  Blue Cloud enter the Red Sequence via different SF quenching modes, and they merge further in a number of dry merging. Galaxy bimodality Baldry et al. 2004 Faber et al. 2007 blue u-r color red U-B color stellar mass

3. 3 A possible picture: A possible picture: blue, star-forming, late-type red, passive, early-type transition populations quenching of SF & morphological transformation Blue galaxies enter the red-sequence in different ways at different masses and times!  Many different galaxies in transition phase ! Introduction Galaxy evolution

4. 4 Introduction Optical CMRs: Optical CMRs: 1-2 Gyr after SF stopped, galaxies red enough to join the red sequence SFR must remain low to stay there NUV CMRs: NUV CMRs: able to distinguish bet. galaxies that have recent SF within the last ~1 Gyr and galaxies that have not. large scatter in the NUV-optical CMR for red ETGs  evidence of low-level recent SF! Why mid-IR? Kaviraj et al. 2007 However, optical/NUV colors are sensitive to dust! NUV-r g-r

5. 5 MIR emission correlates with PAH emission Intermediate-age (> ~ 0.1 Gyr ) stars tracer: MIR emission from ETGs (Bressan et al. 2006): most (13/17) ETGs show a significant broad emission  largely from the circumstellar dust around AGB stars  MIR emission from AGB dust declines with time  MIR emission is sensitive to MIR-weighted mean stellar ages Broad emission features Introduction PAH features MIR can detect the presence of intermediate-age stars and small amounts of ongoing SF in the red-sequence! Why mid-IR? Bressan et al. 2006

6. 6 Piovan et al. 2003 MIR emission  age sensitive  trace past SF activity AGB dust  Piovan AGB dust: SSP models with accounting for circumstellar dust around AGB stars Introduction Why mid-IR? 11 & 15 μ m provide an effective way to study MIR properties!

7. 7  0.07 < z < 0.10 supercluster :  Data: NUV~MIR Imaging: NUV (GALEX), optical (CFHT/Maidanak), NIR (KPNO), MIR (AKARI NEP- Wide survey & CLEVL) Spectroscopy: MMT/Hectospec, WIYN/hydra, Lick/Kast, NED Mullis et al. 2001 1 cluster (A2255) from CLEVL 3 groups (X1, 10, 90) from NEP-Wide survey Data Sample: NEP Supercluster dist. Spatial dist. Redshift dist. Spatial dist.

8. 8 Optical red-sequence  substantially larger scatters in the NUV and MIR CMRs NEP-WideA2255 Results Optical / NUV / MIR CMRs NUV-R N3-S11 B-R

9. 9 Optical red-sequence  substantially larger scatters in the NUV and MIR CMRs NEP-WideA2255 Results Optical / NUV / MIR CMRs NUV-R N3-S11  red : heterogeneous! passively evolving old galaxies recent SF insufficient to alter the optical color  NUV flux is much sensitive to the presence of younger stars dust-obscured SF  S11 traces the MIR emission arising from SF Intermediate-age (> ~0.1 Gyr) stars  S11 traces broad MIR emission from dust surrounding AGB stars B-R

10. 10 Results Using MIR color (N3-S11) classification  MIR blue (N3-S11 < 0): Non-SF  MIR red (N3-S11 > 0): SF Dividing the red-sequence A2255 NEP-Wide sSFR vs. N3-S11 color weak MIR-excess (N3-S11<-1): mean stellar age > 2-5 Gyr intermediate MIR-excess (-1<N3-S11<0): mean stellar age < 2-5 Gyr

11. 11 Results red-sequence galaxies divided into 4 classes: Dividing the red-sequence passively evolving weak-MXG intermediate-MXG weak-SFG dusty-SFG transition phasestar-forming

12. 12 Results Environmental dependence of transition populations optical red optical blue outskirts cores sSFR vs. local density fraction of each galaxy type vs. local density red-sequence transition phase Among massive ones (>10 10 M ⊙ ) at outskirts of clusters, ~70% galaxies are red due to the higher proportion of dusty-SFG and transition galaxies Galaxies in transition phase are the most abundant (~40%)  SF-quenching and morphological transformation take place there

13. 13 Summary We have investigated the MIR properties of optical red-sequence galaxies within a supercluster in the NEP region at z=0.087, using AKARI NEP-Wide survey and CLEVL mission program. AKARI N3-S11 (3-11um) color can be a good indicator of sSFR and the presence of intermediate-age stellar populations. Red-sequence galaxies consist not only of passively evolving red ETGs, but also of (1) disk-dominated SF galaxies that have SFRs lower by ~4 times than blue-cloud galaxies and (2) bulge-dominated galaxies showing stronger MIR dust emission than normal red ETGs. These two populations can be a set of transition galaxies from blue, SF, late-type galaxies evolving into red, quiescent, early-type ones. Transition galaxies are typically found at the outskirts of galaxy clusters. We need to precisely disentangle the origin of MIR excess emission!

14. 14 weak-SF Discussion “red spiral” “optically passive disk” “HI-deficient disk” …  SF shutdown while retaining spiral morphology blue, star-forming, late-type red, passive, early-type quenching of SF & morphological transformation MIR-excess ETG “E+A” “UV-excess ETG” “Blue ETG” …  Early-type morphology while experiencing recent SF Dividing the red-sequence

15. 15 NUR-r vs. W1-W3 (3.4-12um) CCD for volume-limited and flux-limited (Mr<-21.5) galaxies which have little emission lines and place on the red-sequence Discussion NUV-excess and MIR-excess