e. k. grebel globular clusters: the dwarf galaxy contribution1 globular clusters: the dwarf galaxy...
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E. K. Grebel Globular Clusters: The Dwarf Galaxy Contribution
1
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
12Mackey & Gilmore 2004 Salaris & Weiss 2002
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?
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