Globular Clusters and Galaxy Building Blocks

Young-Wook LeeYonsei University, Seoul, Korea

Where are the relics of building blocks that formed stellar component of the Galaxy?

Globular clusters as galaxy building blocks?Peebles & Dicke 1968: “Originated as gas clouds before the galaxies formed”

Freeman 1993: Remaining nuclei of nucleated dwarf ellipticals?

Not all, but some might be…Do we have evidence?

Early hint from spectroscopy (Norris+96) Not just a spread , but discrete RGBs in optical CMD! Multiple pops having different metal (heavier elements) abundances Direct evidence for SNe enrichment Remaining nucleus of a disrupted dwarf galaxy!

(Sollimar+2005)

The 1st Clue: Discovery of Multiple & Discrete RGBs in Cen

Discovery! (Lee+1999, Nature) 130,000 stars

Super-He-rich Subpopulations in CentauriEvidence from MS & New Y2 Isochrones

Model: Lee, Joo+2005Observation: Bedin, Piotto+2004

See also Norris 04; Piotto+05; Sollima+06

Joo & Lee 10, in prep.

Population Z YAge

[Gyr]Fraction

—— 0.0005 0.231 13 +/-0.3 0.42

—— 0.0009 0.232 13 0.27

—— 0.0010 0.38 13 0.17

—— 0.0025 0.39 13 0.08

-—-- 0.006 0.40 13 0.05

Observation: Ferraro et al. 2004

Model: Joo & Lee 2010

in prep.(See also Lee+05)

Super-He-rich Subpopulations in CentauriEvidence from Extended HB (EHB)

Population Z Y [α/Fe] Age [Gyr]

—— 0.0005 0.231 0.3 12.5 +/-0.3

—— 0.0007 0.34 0.3 12.5

—— 0.001 0.232 0.3 11.0

—— 0.009 0.248 0.0 4.0

—— 0.014 0.258 0.0 2.4

Super-He-rich Subpopulation in M54+Sgr Evidence from SGB & EHB (Joo & Lee 10, in prep.)

Siegel+07

For EHB & SGB split

Model

M22 Narrow-band Ca photometryEvidence for SNe enrichment! (J.-W. Lee, Y.-W. Lee+09, Nature)

Ca-by photometryCTIO 1m

Narrow-band Ca & Stromgren b, y filters

hk = (Ca-b) – (b-y)

“a measure of Ca abundance” (Anthony-Twarog+91)

M22 Models (Joo & Lee 10, in prep.)

Obs data : Lee, J.-W. +09

Population Z [Fe/H] [α/Fe] Y Age [Gyr]

—— 0.0004 -1.90 0.3 0.231 12.0 +/-0.3

—— 0.0008 -1.63 0.4 0.310 12.0

Da Costa+09 : [Fe/H] = -1.89 & -1.63Marino+09 : [Fe/H] = -1.82 & -1.68

Both Ca (Fe) & He are enriched in 2nd population!

NGC 288 Ca-by photometry

Presence of double RGBs! (Roh, Lee et al., in prep.)

NGC 288 Models

Population Z [Fe/H] [α/Fe] Y Age [Gyr]

—— 0.00082 -1.592 0.3 0.231 12.7 +/-0.3

—— 0.00120 -1.410 0.3 0.260 11.5

Small Z + Y + t Only weakly extended HB

Metal-rich & He-rich Subpopulation in NGC 1851Evidence from RGB & HB!

(Han+09; CTIO 4m)

U is more sensitive to metal lines!Confirmed by Ca-by photometry(Red: Ca-rich, Blue:Ca-poor: J.-W. Lee+09)

Population Z[α/Fe]

[Fe/H] YAge

[Gyr]Fraction

—— 0.0012 0.3 -1.43 0.232 10.7 0.7

—— 0.0016 0.3 -1.27 0.282 10.6 0.3

Enhancements of (1) “lighter elements” (N, Al, Na; red dotted-line), (2) heavy elements (Ca, Fe…), & (3) He are required.

NGC 1851 Model (Han, Joo+09)

• Very complex!

• It appears that (1) SNe, (2) Fast Rotating Massive Stars, and (3) Intermediate-Mass AGB Stars are ALL involved in the chemical enrichment and pollution in GCs with multiple RGBs.

• GMT can contribute…

Star formation & chemical enrichment history in GCs with multiple RGBs

How do these peculiar GCs differ from “normal” GCs?

Most, if not all, EHB GCs show multiple populations (RGBs)…

Therefore, we use EHB as a proxy for multiple populations (RGBs)…

GCs with extended HB (EHB GCs) = GCs with multiple populations (Lee+07)

GCs with multiple pops (EHB GCs) are distinct from “normal” GCs!

Evidence 1: Presence of SNe enrichment! system was much more massive, was able to withstand SNe winds! M > 107 - 108Msun (i.e., dwarf galaxy)

1. Cen: Y.-W. Lee+99, Bedin+04 (early hint: Norris+96)2. M54 (+Sgr): Sarajedini & Layden 95, Rosenberg+043. NGC 1851: Han+09, J.-W. Lee+09, (Carretta+10)4. M22: J.-W. Lee+09, Marino+09, Da Costa+095. Terzan 5: Ferraro+096. NGC 2419: Cohen+107. And many more? (NGC 288, 362, 1261, 2808, M4, M5, 6218, 6266, 6273,

6723, 6752, 7089…): J.-W. Lee+09, Roh+10

We still need spectroscopic confirmations in many cases!

Evidence 2: EHB GCs are more massive!Lee+2007, ApJ, 661, L49

Early hints:Fusi Pecci+1993Ree+2002Recio-Blanco+2006

Database: Harris 2003

Evidence 3:EHB GCs are kinematically decoupled from normal GCs!

Lee+2007, ApJ, 661, L49

Orbital Kinematics based on Radial Velocity

Database: Harris 2003

(Rgc ≤ 40 kpc) N Vrot σlos Vrot/σlos

All OH ([Fe/H] ≤ -0.8) 59 49±24 100±9 0.49±0.24

EHB 18 4±35 91±15 0.05±0.38

Normal 41 76±30 100±11 0.76±0.31

EHB GCs: Memory of chaoticmerging processes

Normal GCs: Evidence fordissipational collapse!

Occurrence of this by random selection < 1/105 (0.001%) !

Orbital Kinematics based on Full Spatial Motions (35 OH+D/B)(Lee+2007, ApJ, 661, L49)

Evidence 4:EHB GCs are more enhanced in Helium (on average)!

Helium abundance from “R-method”: Data from Salaris+2004

EHB : 0.272±0.008OH+D/B : 0.240±0.006YH : 0.235±0.009

Difference is more than 4!

Evidence 5:EHB GCs are metal-poor!MDF is peaked at [Fe/H] = -1.6 R ≤ 8 Kpc

EHB Candidates+Poor CMDs Normal OH+D/B

EHB GCs are distinct from normal GCs in:

1. SNe enrichment (Multiple RGBs)2. Mass3. Orbital kinematics4. Helium abundance 5. Metallicity distribution function

& Absence of DM is not a serious problem (Saitoh+06)

Fully consistent with a conjecture (Y.-W. Lee+07) that they are relics of primordial Galaxy building blocks!

GMT Sciences?

8.2m VLT FLAMES Spectroscopy:

“Blue MS is more metal-rich!” Implies super Y-rich (Piotto et al. 2005)

Relatively bright (20-21 mag) stars with 8.2m: ~12hrs/cluster

23-25 mag with GMT for all GCs

Better understanding of star formation history in building blocks

GMT Science 1: Multi-Object Spectroscopy of MS stars in Globular Clusters with multiple populations

Cen

GMT Science 2: MOS of GCs in Fornax (H-beta Age Dating & Search for EHB GCs)

Subaru ~10hrs Exp. (S. Kim+10, in prep.)Bright GCs (V < 22.5) in Virgo M87 GMT will provide much better data!

NGC 1399 (CTIO 4m, Kim+09)NGC 1399 (CTIO 4m, Kim+09)

Effect of HB on Balmer lines of Old GCs in M31 (Chung, Lee+2010, in prep.)

Without HB

With HB

Metal-Poor Metal-Rich

Schiavon et al. 2006

Model with He-enhanced pop (zform > 5)Chung, Lee, & Yoon, in prep

GMT Science 3: Balmer Absorption Lines of E galaxies at high-z (1) Passive Evolution or Residual Star Formation?(2) E galaxies prevailed by He enhanced population?

Star formation history in GCs with multiple RGBsA possible scenario?

1. Formation of metal-poor (bluer RGB) stars Normal He, metal-poor, no light-elements enhanced (or depleted)

2. Pollution by fast rotating massive stars Enhance He, and enhance/deplete “lighter elements” Formation of Na-rich O-poor stars (+Mixing )?

3. Most massive (M > 8M⊙) metal-poor stars explode as SNe II Metal enrichment + He enrichment (system was much more massive, was able to withstand SNe winds!) Quenching of SF for a while?

4. Pollution by intermediate-mass (3-7M ⊙ ) AGB stars Add more He, and simultaneously enhance/deplete “lighter elements”

5. Formation of metal-rich (redder RGB) stars from the gas now enriched in overall metallicity, He, and “lighter elements”

Nuclear star clusters in dwarf galaxies are very similar to EHB GCs! (Georgiev+09)

ConclusionThe Three-Stage Formation of the Milky Way

Lee, Y.-W. et al. 2007, ApJ, 661, L49

Present-day Galactic GCs are ensemble of heterogeneous objects originated from three distinct phases of the Milky Way formation!

(1) EHB GCs: remaining cores or relics of primordial Galaxy building blocks expected in the LCDM hierarchical merging paradigm

(2) Normal GCs in the Inner Halo: genuine GCs formed in the dissipational collapse of a transient gas-rich inner halo system that eventually formed the Galactic disk (ELS 1962)

(3) Normal GCs in the Outer Halo: genuine GCs formed in the outskirts of outlying building blocks that later accreted to the outer halo of the Milky Way (Searle & Zinn 1978)

Two pops defined from Na-O anticorrelation are not identical to two pops defined from Ca-by photometry (Han & Lee, in prep.)

For the spectroscopic confirmation of heavy elements difference claimed from Ca-by photometry, stars in two populations defined from photometry should be observed in spectroscopy! (cf. Carretta+10) This critical test has not been done with enough stars (cf. J.-W. Lee+09), but Teff & g should be very well determined in spectroscopy since expected [Fe/H] is comparable to measurement error (0.15 dex)!

Two Pops defined from photometry: No clear separation in Na-O plane (Data from Marino+09,J.-W. Lee+09)

Two Pops defined from Na-O plane: No clear separation in hk CMD

Further works

• What is the ratio of building block candidates to normal GCs?

• More spectroscopic confirmation

• HST WFC3 & ground-based Ca-by photometry of GCs and dwarf galaxies

• Population synthesis with enhanced He population for ETGs

GMT Science 4: NIR AO Imager?Photometry of bright RGB stars in globular clusters & halo fields in

nearby galaxies

If diffraction limited, reliable photometry might be possible to 1-3 mags below RGB tip at Fornax/Virgo distances (Tolstoy 2006; GMT Science Case Nov. 2006).

(1) Measurement of global metallicity from NIR RGB color, such as J-K.(2) Discovery of multiple RGBs, if any ( Cen-like)?(3) distance, etc…