Multi-wavelength Properties and EnvironmentsMulti-wavelength Properties and Environmentsof of the the SDSS Galaxies divided into Fine ClassesSDSS Galaxies divided into Fine Classes

September 16, 2009

Joon Hyeop LeeKorea Astronomy and Space Science Institute

Co-workers: Myung Gyoon Lee (SNU), Changbom Park (KIAS), Yun-Young Choi (ARCSEC)

KASI Colloquium

Many kinds of galaxies with various properties

shape

color

size / luminosity /mass

mass-to-light ratio

surface brightness

spectrum

star formation

AGN activity

How have the various galaxies formed and evolved?

Classifying galaxies and comparing between different types of galaxies.

Which quantity should we use to classify galaxies?

In many previous studies, galaxies have been investigated, using various classifications.

- The three most-frequently-used quantities for galaxy classification are morphology, color and spectral features:

Early-type = Red = Passive ?

Late-type = Blue = Star-forming ?

NOT ALWAYS !

- morphology (early-type vs. late-type; e.g. Choi et al. 2007)

- color (red vs. blue; e.g. Martin et al. 2007)

- spectral features (passive vs. star-forming vs. AGN; e.g. Mateus et al. 2006)

Among those several major criteria, only one criterion used to be adopted for galaxy classification in most previous studies.

Blue early-type galaxies: elliptical morphology, but blue color

- Abraham et al. 1999; Ferreras et al. 2005; Lee et al. 2006

Passive spiral galaxies: spiral morphology, but no signal of current star formation

- Couch et al. 1998; Goto 2003; Yamauchi & Goto 2004

Mutilateral Classification

(1) Morphology (2) Color (3) Spectral Features

Park & Choi (2005)

Early-type

Late-type

Lee et al. (2006)

Red

Blue

Kauffmann et al. (2003)Kewley et al. (2006)

AGN

HII

LINER

Seyfert

→ Early-type galaxiesLate-type galaxies

→ Red galaxiesBlue galaxies

→ Passive, HII, Seyfert, LINER

morphology

color

spectral features

blue

red

early-type

late-type passiveHII

Seyfert LINER

Sample Selection

K-correction: Blanton et al. (2003) Evolutionary correction: Tegmark et al. (2004)

Completeness limit: 14.5<rpet<17.77

Most physical properties of galaxies are known to be dependent on their velocity dispersion.

In each quantities, sampling errors were estimated by calculating the standard deviation of the median values in 200-times repetitive samplings.

“The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features - I. Optical properties”,

Lee et al. (2008) MNRAS, 389, 1791

“The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features - I. Optical properties”,

Lee et al. (2008) MNRAS, 389, 1791

pREG

hREG

pBEG

hBEG

Compared to pREG:less concentratedbluer outskirtless spheroidal

Compared to pREG:totally bluersimilarly concentrated

Compared to pBEG:bluer centermore concentrated

hREG : early-type galaxies with small disk components? (gas infall?)

hBEG: objects in the final phase of early-type formation? (galaxy merger?)

Star formation in REGs is dominant in their outskirt, while star formation in BEGs is dominant in their center?

Different origins of star formation

RLGs have smaller axis ratio than that of BLGs on average.

Late-type galaxies with large inclination may beoften classified as RLGs due to dust extinction.

RLG BLG

At axis ratio > 0.6 (small inclination),RLGs are more concentrated than BLGs.

One major origin of the red color of RLGsmay be their large bulge fraction.

BLGRLG

pRLGs are similar to REGs in many aspects (color, axis ratio, Dn(4000), and so on), although they are less concentrated than typical REGs.

These may be intermediate between early-type and late-type.

(1) REGs show narrowly-ranged median colors, which are consistent with the 6 – 8 Gyr old SSP model.

pREGs have slightly bluer color than the other REGs: metallicity effect? (comp. metallicity estimation of Gallazzi et al. 2006)

(2) pBEGs, lBEGs vs. hBEGs, sBEGs: SSP + EXP model?

“The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features - II. Multi-wavelength properties”,

Lee et al. (2009) MNRAS, submitted

(3) The colors of pRLGs are similar to those of REGs, but RLGs (rectangles) are located on a sequence from REG colors to decreasing (u – r ) color.

→ red bulge + SF disk

(4) pBLGs seem to have very young mean stellar ages, although they are spectroscopically passive. → passive only in the center,

or recent SF quenching?

“The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features - II. Multi-wavelength properties”,

Lee et al. (2009) MNRAS, submitted

BLGs are better detected than RLGs, which shows that the dominant factor to make RLGs red may be the bulge-to-disk ratio rather than dust contents.

IRAS detection fraction

Best et al. (2005) and Croft et al. (2007) showed that the fraction of radio-loud AGN host galaxies is a strong function of stellar mass.

Early-type radio source: radio-loud AGNs.

Late-type radio source: star formation regions.

FIRST detection fraction

Discussion

1. Bulge formation vs. Disk formation- Bulge: hBLGs → (merging) → hBEGs → sBEGs (lBEGs) → pBEGs

→ pREGs?

- Disk: pREGs → hREGs → sREGs, lREGs (→ pREGs)?

pREGs → hRLGs → sRLGs, lRLGs (→ pRLGs)?

Discussion

2. The role of Environments- High local number density: accelerates the evolution of galaxies by

means of frequent merging and interaction.

e.g.) pREGs ------- hBEGs ------- hBLGs

- Close neighbor: directly affects star formation by either preventing it or stimulating it (according to the property of the close pair).

Sometimes affects the AGN type?

e.g.) sBLGs vs. lBLGs

- Galaxy cluster: hinders the AGN activity in most red galaxies.

e.g.) sREGs, lREGs, lRLGs

Open question: Why galaxy cluster environments do not seem to prevent the star formation of red galaxies, while they prevent the AGN activity of red galaxies?

Future Works

1. To study more detailed properties of several fine classes that show some remarkable features.

e.g.) Red HII galaxies in cluster environments

Blue early-type galaxies (AKARI spectroscopy)

Radio-loud passive galaxies

and so on…

- Internal structure analysis

2. To expand this study to intermediate and high redshifts.e.g.) GOODS, UDF, DEEP2, SPITZER, AKARI,

or some future observations.

- Redshift evolution of the fine classes