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Globular Clusters and Galaxy Building Blocks. Young-Wook Lee Yonsei University, Seoul, Korea. Where are the relics of building blocks that formed stellar component of the Galaxy? Globular clusters as galaxy building blocks?

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globular clusters and galaxy building blocks
Globular Clusters and Galaxy Building Blocks

Young-Wook Lee

Yonsei 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?


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

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!

Discovery!(Lee+1999, Nature)

130,000 stars



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

Model: Lee, Joo+2005

Observation: Bedin, Piotto+2004

See also

Norris 04; Piotto+05;


Joo & Lee 10, in prep. 


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

Observation: Ferraro et al. 2004


Joo & Lee 2010

in prep.

(See also Lee+05)


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



 For EHB & SGB split

m22 narrow band ca photometry evidence for sne enrichment j w lee y w lee 09 nature
M22 Narrow-band Ca photometryEvidence for SNe enrichment! (J.-W. Lee, Y.-W. Lee+09, Nature)

Ca-by photometry


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

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

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

Marino+09 : [Fe/H] = -1.82 & -1.68

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

ngc 288 models
NGC 288 Models

Small DZ + DY + Dt

 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)


NGC 1851 Model (Han, Joo+09)

Enhancements of (1) “lighter elements”

(N, Al, Na; red dotted-line), (2) heavy elements

(Ca, Fe…), & (3) He are required.


Star formation & chemical enrichment history in GCs with multiple RGBs

  • 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…
how do these peculiar gcs differ from normal gcs
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)

  • w Cen: Y.-W. Lee+99, Bedin+04 (early hint: Norris+96)
  • M54(+Sgr): Sarajedini & Layden 95, Rosenberg+04
  • NGC 1851:Han+09, J.-W. Lee+09, (Carretta+10)
  • M22: J.-W. Lee+09, Marino+09, Da Costa+09
  • Terzan 5: Ferraro+09
  • NGC 2419: Cohen+10
  • 7.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

Database: Harris 2003

Early hints:

Fusi Pecci+1993




Evidence 3:

EHB GCs are kinematically decoupled from normal GCs!

Lee+2007, ApJ, 661, L49

Orbital Kinematics based on Radial Velocity

Database: Harris 2003


Orbital Kinematics based on Full Spatial Motions (35 OH+D/B)

(Lee+2007, ApJ, 661, L49)

EHB GCs: Memory of chaotic

merging processes

Normal GCs: Evidence for

dissipational collapse!

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


Evidence 4:

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

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

EHB : 0.272±0.008

OH+D/B : 0.240±0.006

YH : 0.235±0.009

Difference is more than 4s!


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
EHB GCs are distinct from normal GCs in:

1. SNe enrichment (Multiple RGBs)

2. Mass

3. Orbital kinematics

4. 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 science 1 multi object spectroscopy of ms stars in globular clusters with multiple populations
GMT Science 1:Multi-Object Spectroscopy of MS stars in Globular Clusters with multiple populations

w Cen

  • 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 2 mos of gcs in fornax h beta age dating search for ehb gcs
GMT Science 2: MOS of GCs in Fornax (H-beta Age Dating & Search for EHB GCs)

NGC 1399 (CTIO 4m, Kim+09)

Subaru ~10hrs Exp. (S. Kim+10, in prep.)

Bright GCs (V < 22.5) in Virgo M87

 GMT will provide much better data!

effect of hb on balmer lines of old gcs in m31 chung lee 2010 in prep
Effect of HB on Balmer lines of Old GCs in M31 (Chung, Lee+2010, in prep.)

Without HB

With HB

Metal-Poor Metal-Rich


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?

Model with He-enhanced pop (zform > 5)

Chung, Lee, & Yoon, in prep

Schiavon et al. 2006


Star formation history in GCs with multiple RGBs

A 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”

conclusion the three stage formation of the milky way lee y w et al 2007 apj 661 l49
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.)

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

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 D[Fe/H] is comparable to measurement error (0.15 dex)!

further works
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 (w Cen-like)?

(3) distance, etc…