E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Globular Clusters:The Dwarf Galaxy Contribution

Eva K. GrebelAstronomisches Rechen-Institut (ARI)

Center for Astronomy, Heidelberg University (ZAH)Heidelberg, Germany

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

2Zinn 1985

–0.8 dex

Halo disk/bulge

bulge/disk GCsold halo GCs“young” halo GCsSgr GCs

Harris 1996Mackey & Gilmore 2004

van den Bergh (1995): stronger trend with perigalactic distances

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Mackey & van den Bergh 2005

Cumulative radial distributionof different subcomponents

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Zinn 1993

Horizontal Branch Morphology vs. Metallicity: Age?

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Horizontal Branch Morphologies and Young Halo Contributors

Mac

key

& G

ilmor

e 20

04

t = 0 Gyr

t = 1.1 Gyr

t = 2.2 Gyr

See also Harbeck et al. 2001

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Horizontal Branch Morphologies and Young Halo Contributors

Mac

key

& G

ilmor

e 20

04

t = 0 Gyr

t = 1.1 Gyr

t = 2.2 Gyr

See also Harbeck et al. 2001

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Horizontal Branch Morphologies and Young Halo Contributors

Mac

key

& G

ilmor

e 20

04

t = 0 Gyr

t = 1.1 Gyr

t = 2.2 Gyr

See also Harbeck et al. 2001

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Glatt et al. 2007

SMC:Only nearbydwarf withonly one, younger GC.(HST/ACS)

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Buonanno et al. 1998

4 (out of 5) globularclusters in Fornax:~ indistinguishablein age; as old as oldestGalactic globulars(relative age dating).

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Mackey & Gilmore 2004

bulge/disk GCsold halo GCs“young” halo GCsSgr GCs

Salaris & Weiss 2002Harris 1996

Age Difference vs. Metallicity

Old halo: slight trend (towards bulge)Young halo: steeper trend (towards Sgr)

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Sbordone et al. 2007

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)

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Narrowpeak;Age ~–2 Gyr.

Stronglypeaked atAge ~ M92.Younger tail(incl. CMa?)

Bimodal;peaked at–3.25 and–0.75 Gyr.

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Mac

key

& G

ilmor

e 20

04

Similarity of Core Radii of Young Halo and External GCs

If dwarfs were accreted: would contribute mainly young halo GC;only 20 – 20% old halo GCs.

Zinn 1993

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Mac

key

& v

an d

en B

ergh

200

5

Tidal Radii for Clusters of Different Components

Rt: stronglycorrelated witha GC’s peri-galactic distance(van den Bergh1994).

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Gne

din

& O

strik

er 1

997

“Vital Diagram” for Galactic Globular Clusters

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Mac

key

& v

an d

en B

ergh

200

5

shar

p ed

ge

Cores of dwarfgalaxies?

Half-light Radii vs. Absolute Magnitudes

17Globular Clusters: The Dwarf Galaxy Contribution

E. K. Grebel Grebel 2002

Globular clusters are rare in dwarfs!

E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution

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Some points for discussion:

Young halo globulars (HB morph.) resemble dSph globularsBUT: a number with "old" HB morphologies

DSphs (and dIrrs) contain some of the youngest globulars knownBUT: 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?