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 Uni-

verse

2

Introduction

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. 2007blue u-r color red

U-B

col

or

stellar mass

3

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 !

IntroductionGalaxy evolution

4

Introduction

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: 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

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 emis-sion

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 intermedi-ate-age stars and small amounts of ongoing

SF in the red-sequence!

Why mid-IR?Bressan et al. 2006

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

IntroductionWhy mid-IR?

11 & 15 μm provide an effec-tive

way to study MIR proper-ties!

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/Hec-tospec, WIYN/hydra, Lick/Kast, NED

Mullis et al. 2001

1 cluster (A2255) from CLEVL3 groups (X1, 10, 90) from NEP-Wide survey

DataSample: NEP Supercluster

Redshift dist. Spatial dist.

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

Optical red-sequence substantially larger scatters in the NUV and MIR CMRs

NEP-WideA2255

ResultsOptical / 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

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

Results

red-sequence galaxies divided into 4 classes:

Dividing the red-sequence

passively evolving

weak-MXG intermediate-MXG weak-SFG dusty-SFG

transition phase star-forming

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 (>1010 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

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

weak-SF

Discussion

“red spiral”“optically passive disk”“HI-deficient disk”… SF shutdown while retaining spi-ral 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 mor-phology while experiencing recentSF

Dividing the red-sequence

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

DiscussionNUV-excess and MIR-excess