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Globular Clusters: The Dwarf Galaxy Contribution

Globular Clusters: The Dwarf Galaxy Contribution. Eva K. Grebel Astronomisches Rechen-Institut (ARI) Center for Astronomy, Heidelberg University ( ZAH ) Heidelberg, Germany. van den B ergh (1995): stronger trend with perigalactic distances. Halo disk/bulge. –0.8 dex. Zinn 1985.

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Globular Clusters: The Dwarf Galaxy Contribution

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  1. Globular Clusters: The Dwarf Galaxy Contribution Eva K. Grebel Astronomisches Rechen-Institut (ARI) Center for Astronomy, Heidelberg University (ZAH) Heidelberg, Germany Globular Clusters: The Dwarf Galaxy Contribution

  2. van denBergh (1995): stronger trend with perigalactic distances Halo disk/bulge –0.8 dex Zinn 1985 bulge/disk GCs old halo GCs “young” halo GCs Sgr GCs Globular Clusters: The Dwarf Galaxy Contribution Harris 1996 Mackey & Gilmore 2004

  3. Cumulative radial distribution of different subcomponents Mackey & van den Bergh 2005 Globular Clusters: The Dwarf Galaxy Contribution

  4. Horizontal Branch Morphology vs. Metallicity: Age? Zinn 1993 Globular Clusters: The Dwarf Galaxy Contribution

  5. Horizontal Branch Morphologies and Young Halo Contributors t = 0 Gyr Mackey & Gilmore 2004 t = 1.1 Gyr t = 2.2 Gyr See also Harbeck et al. 2001 Globular Clusters: The Dwarf Galaxy Contribution

  6. Horizontal Branch Morphologies and Young Halo Contributors t = 0 Gyr Mackey & Gilmore 2004 t = 1.1 Gyr t = 2.2 Gyr See also Harbeck et al. 2001 Globular Clusters: The Dwarf Galaxy Contribution

  7. Horizontal Branch Morphologies and Young Halo Contributors t = 0 Gyr Mackey & Gilmore 2004 t = 1.1 Gyr t = 2.2 Gyr See also Harbeck et al. 2001 Globular Clusters: The Dwarf Galaxy Contribution

  8. SMC: Only nearby dwarf with only one, younger GC. (HST/ACS) Glatt et al. 2007 Globular Clusters: The Dwarf Galaxy Contribution

  9. 4 (out of 5) globular clusters in Fornax: ~ indistinguishable in age; as old as oldest Galactic globulars (relative age dating). Buonanno et al. 1998 Globular Clusters: The Dwarf Galaxy Contribution

  10. Age Difference vs. Metallicity bulge/disk GCs old halo GCs “young” halo GCs Sgr GCs Old halo: slight trend (towards bulge) Young halo: steeper trend(towards Sgr) Salaris & Weiss 2002 Harris 1996 Mackey & Gilmore 2004 Globular Clusters: The Dwarf Galaxy Contribution

  11. Lower [/Fe] at a given [Fe/H] in dwarfs and their globulars (few exceptions, e.g., Hodge 1; NGC 121) Cf. inner/outer halo dichotomy (Carollo et al. 2007) Sbordone et al. 2007 Globular Clusters: The Dwarf Galaxy Contribution

  12. Narrow peak; Age ~ –2 Gyr. Bimodal; peaked at –3.25 and –0.75 Gyr. Strongly peaked at Age ~ M92. Younger tail (incl. CMa?) Globular Clusters: The Dwarf Galaxy Contribution Mackey & Gilmore 2004 Salaris & Weiss 2002

  13. Similarity of Core Radii of Young Halo and External GCs Mackey & Gilmore 2004 If dwarfs were accreted: would contribute mainly young halo GC; only 20 – 20% old halo GCs. Zinn 1993 Globular Clusters: The Dwarf Galaxy Contribution

  14. Tidal Radii for Clusters of Different Components Rt: strongly correlated with a GC’s peri- galactic distance (van den Bergh 1994). Mackey & van den Bergh 2005 Globular Clusters: The Dwarf Galaxy Contribution

  15. “Vital Diagram” for Galactic Globular Clusters Gnedin & Ostriker 1997 Globular Clusters: The Dwarf Galaxy Contribution

  16. Half-light Radii vs. Absolute Magnitudes Cores of dwarf galaxies? sharp edge Mackey & van den Bergh 2005 Globular Clusters: The Dwarf Galaxy Contribution

  17. Globular clusters are rare in dwarfs! Globular Clusters: The Dwarf Galaxy Contribution Grebel 2002

  18. Some points for discussion: • Young halo globulars (HB morph.) resemble dSph globulars • BUT: a number with "old" HB morphologies • DSphs (and dIrrs) contain some of the youngest globulars known • BUT: Also contain globulars as old as oldest Galactic GCs • Half-light and tidal radii of young halo GCs and GCs in dwarfs: Close similarity. • Hint of accretion or effect of survivability in absence of major tidal disruption? • Overall metallicities of outer halo GCs and dwarf GCs: similar; low. • Lower [/Fe] at given [Fe/H] in dwarf field stars and GCs. (Constrains number of accretion events) • GCs in MW with similar ratios: Assumed to be accreted (e.g., Sgr) • BUT: Also (d)Irrs contain some GCs with enhanced [/Fe]! • Accretion: consistent. But is it required? • Substructure problem; number, importance, time of accretion events • How can GCs form in dSphs in the first place? Why so rare? Globular Clusters: The Dwarf Galaxy Contribution

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