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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?

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Globular Clusters and Galaxy Building Blocks

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  1. Globular Clusters and Galaxy Building Blocks Young-Wook Lee Yonsei University, Seoul, Korea

  2. 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?

  3. 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 (Sollimar+2005)

  4. 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; Sollima+06 Joo & Lee 10, in prep. 

  5. Super-He-rich Subpopulations in w CentauriEvidence from Extended HB (EHB) Observation: Ferraro et al. 2004 Model: Joo & Lee 2010 in prep. (See also Lee+05)

  6. Super-He-rich Subpopulation in M54+SgrEvidence from SGB & EHB (Joo & Lee 10, in prep.) Siegel+07 Model  For EHB & SGB split

  7. M22 Narrow-band Ca photometryEvidence for SNe enrichment! (J.-W. Lee, Y.-W. Lee+09, Nature) Ca-by photometry CTIO 1m Narrow-band Ca &Stromgren b, y filters hk = (Ca-b) – (b-y) “a measure of Ca abundance” (Anthony-Twarog+91)

  8. 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!

  9. NGC 288 Ca-by photometryPresence of double RGBs! (Roh, Lee et al., in prep.)

  10. NGC 288 Models Small DZ + DY + Dt  Only weakly extended HB

  11. 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)

  12. 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.

  13. 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…

  14. 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)

  15. 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!

  16. Evidence 2: EHB GCs are more massive! Lee+2007, ApJ, 661, L49 Database: Harris 2003 Early hints: Fusi Pecci+1993 Ree+2002 Recio-Blanco+2006

  17. Evidence 3: EHB GCs are kinematically decoupled from normal GCs! Lee+2007, ApJ, 661, L49 Orbital Kinematics based on Radial Velocity Database: Harris 2003

  18. 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%) !

  19. 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!

  20. 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

  21. 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!

  22. GMT Sciences?

  23. 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

  24. 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!

  25. Effect of HB on Balmer lines of Old GCs in M31 (Chung, Lee+2010, in prep.) Without HB With HB Metal-Poor Metal-Rich

  26. 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

  27. 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”

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

  29. 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)

  30. 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)!

  31. 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

  32. 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…

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