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?
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!
Super-He-rich Subpopulations in w CentauriEvidence from MS & New Y2 Isochrones
Model: Lee, Joo+2005
Observation: Bedin, Piotto+2004
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
(See also Lee+05)
Super-He-rich Subpopulation in M54+SgrEvidence from SGB & EHB (Joo & Lee 10, in prep.)
For EHB & SGB split
Narrow-band Ca &Stromgren b, y filters
hk = (Ca-b) – (b-y)
“a measure of Ca abundance” (Anthony-Twarog+91)
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!
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
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)
Evidence 2: EHB GCs are more massive!
Lee+2007, ApJ, 661, L49
Database: Harris 2003
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
Normal GCs: Evidence for
Occurrence of this by random selection < 1/105 (0.001%) !
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!
EHB GCs are metal-poor!
MDF is peaked at [Fe/H] = -1.6
R ≤ 8 Kpc
1. SNe enrichment (Multiple RGBs)
3. Orbital kinematics
4. Helium abundance
5. Metallicity distribution function
& Absence of DM is not a serious problem (Saitoh+06)
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!
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”
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)!
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…