globular clusters and galaxy building blocks
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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? - PowerPoint PPT PresentationTRANSCRIPT
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Globular Clusters and Galaxy Building Blocks
Young-Wook LeeYonsei University, Seoul, Korea
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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?
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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
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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
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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)
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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
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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)
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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!
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NGC 288 Ca-by photometry
Presence of double RGBs! (Roh, Lee et al., in prep.)
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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
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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)
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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)
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• 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
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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)
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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!
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Evidence 2: EHB GCs are more massive!Lee+2007, ApJ, 661, L49
Early hints:Fusi Pecci+1993Ree+2002Recio-Blanco+2006
Database: Harris 2003
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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
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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)
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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!
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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
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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!
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GMT Sciences?
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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
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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)
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Effect of HB on Balmer lines of Old GCs in M31 (Chung, Lee+2010, in prep.)
Without HB
With HB
Metal-Poor Metal-Rich
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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?
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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”
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Nuclear star clusters in dwarf galaxies are very similar to EHB GCs! (Georgiev+09)
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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)
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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
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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
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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…