Formation of Mas-sive Early-type Gal-

axies

Myung Gyoon Lee Seoul National University, Korea

2014.11.6

The 6th KIAS Workshop on Cosmology and Structure Formation, Nov 4-7, 2014 , KIAS , Seoul

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Massive ETGs are rare in the field.

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Massive ETGs are abundant in massvie clusters!

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Superclusters are an ideal lab for seeing galaxy evolution!

SDSS DR7 + WISE study of ETGs (red) and LTGs (blue) in A2199 (GH Lee, HS Hwang, MG Lee et al. 2014, ApJ, submitted , Poster)

three clus-ters + four groups +

something else

Morphology from KIAS VAGC

Galaxy evolution in the MIR C-L diagram

Late-type MIR SF sequence galaxies

Late-type MIR green valley galaxies

Early-type MIR green valley galaxies

Early-type MIR blue cloud galaxies

Star formation quenching

Morphology transformation

several Gyr

Opt GV

Various surveys & simulations lead to re-markable advances in understanding of formation and evolution of massive galax-ies.

Formation of Massive ETGs in 2014

6 However,

(NASA/STScI)

However, most methods are based on inte-grated stellar light! (Limits) 1) Observing mostly only the inner regions of galaxies, seeing only a tip of an iceberg!2) Difficult to distinguish multiple popula-tions!

Current limits for Massive ETG stud-ies

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(1) Ghost light in galaxy clus-ters?

Intracluster light is also abundant in clus-ter!

It is bluer than massive galaxies! (Montes+2014: A2744)

Its origin? Heavy or light galaxies?

Stellar Halos! Not dark, but very faint!

1) Do massive ETGs have a single halo (spheroid) or multiple halos?2) How different are halos in E galaxies from bulges in disk galaxies?3) How did these halos form?

(2) Unknowns for Massive ETGs

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Note that stellar halos occupy not only the outer region but also the inner region of a galaxy!

(Two powerful probes)1) Globular clusters (GCs), tracing halos.2) Resolved stars, showing directly stellar halos!

How to Study Stellar Halos?

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Color distributions of GCs are bimodal, showing blue (metal-poor) GCs and red (metal-rich) GCs. Both may be older than 10 Gyr (corresponding to

z>2).

Globular Clusters in Massive ETGs in Virgo

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Globular Clusters in M49 (Geisler, Lee, & Kim 1996, AJ, Lee et al

1998, AJ)

color

The blue GC system looks circular, while the red GC system is more elongated.

-Why both systems in a galaxy show difference?

-Is M49 special? -Is this common among

massive ETGs? -What does it tell about

galaxy formation?

An Old Mystery on GCs in M49

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Globular Clusters in M49

(Lee, Kim & Geisler 1998 AJ)

Blue GC : Red GC

To answer these questions, we need

A systematic study for a large sample of ETGs! (Park & Lee 2013, ApJL, 773, L27)

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An example: M59 (E5) Gray: GCs in 100 galax-

ies Color: M59

(Shapes of the GC sys-tems) The red GC system is more elongated than the blue GC system.

Gems in HST/ ACSVCS!

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Data: homogeneous set of gz photometry of GCs in 100 Virgo ETGs (Cote+2004, Peng+2006, 2008, Jordan+2009) – gray map

Small field of view, but excellent quality!

Ellipticity of the red GC systems shows a tight 1:1 correlation with galaxy stellar light,

while the blue GC systems do much less.

Ellipticity of GC systems vs galaxy

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Ellip

ticit

y (

GC

syste

m)

Ellipticity (galaxy stel-lar light)

Red GC systems show a strong correlation with Mv (galaxy): fainter galaxies have more elongated red GC systems.

Blue GC systems show little correlation with Mv.

Ellipticity (GC System) vs Mv(galaxy)

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Ellipticity of the red GC systems shows a strong correlation with rotation of their host galaxy: the faster galaxies rotate, the more elongated their red GCSs are.

In contrast, the blue GC systems do little.

Ellipticity (GC system) vs Rotation (galaxy)

17Rotational parameter (star)[AT-LAS 3D]

e(G

CS

-sta

r) e

llip

ticit

y

(GC

S)

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What can we make it out of it?

Massive ETGs have dual halos!

A blue halo and a red halo. Yin & Yang model?

A new view for ETG structures!

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Old view

New view

Lee+ (2013)

The blue halo (metal-poor)◦Rounder, More extended◦Non-rotating?

The red halo (metal-rich)◦Main body of ETGs◦Strong correlation with

stars◦Elongated, Compacter◦Rotating?

Dual Halos in ETGs

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Globular Clusters in M49

(Lee, Kim & Geisler 1998 AJ)

Blue halo : Red halo

A large scale map of the GCs in Virgo

21Lee, Park & Hwang (2010, Science):

SDSS

Number density maps of GCs

Substructures around massive galaxies

Diffuse large scale structure-Intracluster GCs (wandering GCs) !!!

The blue halos are much larger than the red halos!

(radial density profiles are flatter). Intracluster GCs are mostly blue GCs! (old &

metal-poor)

Blue GCs and Red GCs in Virgo

22Lee, Park & Hwang (2010, Science): SDSS

Blue GCs : Red GCs

What about Stellar Halos?

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Standard E galaxy at 10 Mpc.

M105, E1 in Leo Group

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M105-W

M105-SE Reff = 0’.93

Reff = 0’.55

14.9 kpc5’

+

+

12 Reff

Michel-Dansac+2010,CFHT/Megacam

M105 (Harris+ 2007 (SE field), Lee & Jang 2014)

Resolved stars show two RGB pops: Blue (metal-poor) RGB and Red (metal-rich)

RGBs!

Resolved Stars in Es

25Lee & Jang (2014, in prep)Blue: Red

RGB

Two components Metal-rich stars dom-

inate in the inner re-gion.

Metal-poor stars get significant in the outer region.

Radial Density Profiles of Stars in M105

26Lee & Jang (2014, in prep)

Two components Inner region(3-7 Reff): the red RGB domi-nates

Outer region(10-13Reff): the blue RGB gets stronger, while the peak metallicity of the red RGB remains con-stant.

Metallicity Distributions of Stars in M105

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Metallicity, [M/H]

Showing two stellar ha-los: blue and red.

Consistent with GC ha-los!

Inner re-gion

Outer re-gion

Blue: Red RGB

Lee & Jang (2014, in prep)

Discovery of an ultra-faint dwarf galaxy (UFD) in the Virgo: a fossil of the first galaxies?

(Jang & Lee 2014 Nov 1, ApJL, 795, L6)

+

Virgo cluster

Mihos+2005

+

Virgo cluster

Mihos+2005

+

Virgo cluster

Mihos+2005

HST field (Williams+07)

F606W ~ 63000sF814W ~ 27000s

dSph-D07(Durrell+07)

+

Virgo cluster

Mihos+2005

HST field (Williams+07)

F606W ~ 63000sF814W ~ 27000s

dSph-D07(Durrell+07)

+

Virgo cluster

Mihos+2005

HST field (Williams+07)

F606W ~ 63000sF814W ~ 27000s

dSph-D07(Durrell+07)

New galaxy

8" × 8"

Color magnitude diagrams

20” x 20”

dSph-D07 (m-M)0 = 31.19± 0.05

(d = 17.3 ± 0.4 Mpc)

[Fe/H] = -2.4± 0.4

Existence of AGB

Color magnitude diagrams

20” x 20”

dSph-D07

10” x 10”

New galaxy

(m-M)0 = 31.19± 0.05

(d = 17.3 ± 0.4 Mpc)

[Fe/H] = -2.4± 0.4

Existence of AGB

(m-M)0 = 31.08± 0.05

(d = 16.4 ± 0.4 Mpc)

[Fe/H] = -2.4± 0.4

No AGB stars

Color magnitude diagrams

20” x 20”

dSph-D07

10” x 10”

Virgo-UFD1

(m-M)0 = 31.19± 0.05(d = 17.3 ± 0.4 Mpc)[Fe/H] = -2.4± 0.4Existence of AGB stars (m-M)0 = 31.08± 0.05(d = 16.4 ± 0.4 Mpc)[Fe/H] = -2.4± 0.4No AGB stars

A new galaxy is

a genuine member of Virgo cluster. very metal poor ([Fe/H] ~ -2.4). very old (age > 10 Gyr). ultra-faint (Mv= -6.5) dwarf small (R(eff) = 81 pc). UFDs (as well as dSphs) may be the origin of

the blue halos and ICL?

Formation of Massive ETGs

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Two mode forma-tion!

1) Red halo mode◦ In situ formation via dissipative

collapse/merger ◦Mostly metal-rich stars◦Starting from a or more massive

progenitors with rotation

2) Blue halo mode◦Dissipationless merger/accre-

tion◦Mostly metal-poor stars ◦Mostly from dwarf galaxies

To be tested with simula-tions.

Implication for Size Evolution

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Current idea to explain size evolution of ETGs: progenitors of massive ETGs formed at z>3 and grew via minor merger at z<2.

However, measured Reffs are based on metal-rich stars, i.e., the red halo! They do not recognize the existence of the blue halo.

Implication for Size Evolution

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Current idea to explain size evolution of ETGs: progenitors of massive ETGs formed at z>3 and grew via minor merger at z<2.

However, measured Reffs are based on metal-rich stars, i.e., the red halo! They do not recognize the existence of the blue halo.

Possibilities: 1) dry merging of intermediate mass galaxies,

not of dwarf galaxies. 2) wet merging of gaseous galaxies 3) Two phase formation scenarios should be

three: two for red halos and one for blue halos.

Summary

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Massive galaxies have dual ha-los!

We are seeing mostly the red halos embedded in much larger blue halos!

Massive galaxies formed in red and blue modes.

New view