이광호 ( 서울대학교 )

Galaxy Classification in the WISE Color-Luminos-

ity Diagram

우주탐사회 워크샵 @ 무주리조트 2014. 2. 10. ~ 12.

SDSS DR10 WISE

Optical Color-Magnitude Diagram

Red quiescent galaxies, mainly

ETGs

Blue star-forming galaxies, mainly

LTGsMasters+11

Green Valley

Galaxy Migration in CMD

Faber+07

In terms of - SF quenching - Mass buildup

A Key QuestionDid quenching occur early in the process of mass buildup, midway, or late?

The transition timescale must be short (~ 1 Gyr)!!

Since the color bimodality will never be seen if the transition timescale is over a Hubble time (Pan+10).

To understand galaxy evolution,

Galaxy classification based on MIR colors

Quiescent galaxies

Transition Objects

Star-forming galaxies

AK

AR

I (N

3-S1

1) c

olor

Shim+2011

Spectral Energy Distribution

da Cunha+08

Unattenuated stellar spectrum

Emission by dust in stellar birth cloud

Emission by dust in the ambient ISM

(Model) SED of Starburst galaxies

Observed SED

Multi-wavelength dataSDSS DR10 + WISE combined galaxy catalogWide-field Infrared Survey Explorer (WISE)

– All sky survey – four MIR bands (3.4, 4.6, 12, 22μm)

79,579 galaxies at 0.01< z <0.06- S/N12μm > 5 - Excluding AGNs

GALEX NUV data

CLDMIR CLD WISE [3.4] – [12]

≈ AKARI N3 – S11

MIR star-forming se-quence (Hwang +13): SFR ~ Mass relation

MIR emission from AGB dust (Piovan+03): SSP with different ages (1~10 Gyr)

Early-type galaxies

Piovan+03young

old

The second population spans [3.4] – [12] corre-sponding the colors of ETGs with MIR-excess

cover.

Mean age

Late-type galaxies

MIRC: deviation of [3.4] – [12] from the SFSG (red line)

A left long tail: MIRC < -1 mainly LTGs w/o SF nuclei

MIR Galaxy Classification

MIR star-forming se-quence

MIR blue clump

MIR green val-ley

vs. Optical CMD

MIR green valley ≠ Optical green valley

Transition timescale from MIR GV to MIR BC: ~ # Gyrs

MIR GV → MIR BC: optically red galaxies w/ RSF → DEAD galaxies

NUV – r vs. [3.4] – [12]

Two-component SSP model: small amount of young (0.5, 1, 2 Gyr) populations make galaxies have MIR-excess emis-sion (MIR GV).

NUV-excess galaxies (NUV – r > 5.4)

→ MIR-excess galaxies → Quiescent galaxies (Ko+13)

NUV is sensitive to very recent (<1 Gyr) SF, MIR is sensitive to SF over longer timescale.

NUV – r colors of MIR GV and MIV BC are overlapped.

ATLAS3D

Cappellari+13

Multi color imaging + 2D kinematics for 260 ETGs (d < 42 Mpc)

Slow / Fast Rotators

Emsellem+13

ConclusionWe present a new galaxy classification scheme in the

WISE [3.4] – [12] color vs. 12μm luminosity diagram.

We classify galaxies into three types: MIR star-form-ing galaxies, MIR green valley galaxies, MIR blue clump galaxies.

To obtain a better understanding of galaxy evolution, we need to focus on RGB of galaxies.