Globular Cluters in Dwarf Galaxies

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Globular Cluters in Dwarf Galaxies
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But first, a digression regarding tides . . .
Leo I
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For our purposes at this workshop, dwarf galaxy
baryons consist of Field stars and
gas Clusters
What would be learn if we considered one of
these components, ignoring the other?
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Stars and gas only . . . This is largely how we
consider dwarfs at present
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But what if we consider only the clusters? What
would we see?
We would still detect DM halos
Fornax
Cluster Vh 2 52.1 3
60.4 4 47.4 5 62.0
? 1 deg ?
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Sgr
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We can even say something about the nature of
these halos Mass velocity dispersion from
clusters. Recall this industry started with
N3. Fornax N4, sGC 6.0 km/s
MGC/M 0.6 but M/L gtgt 100 Mass
distribution DM not cuspy.
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UMi
Survival of Fornax and dE GCs imply cored DM
halos to avoid Dyn Friction nucleation.
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The GCs alone also reveal a range in SF history
and metallicity. . .
. . . albeit a somewhat less interesting picture
than the field stars reveal.
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From the clusters alone, we could conclude --
These are useful tracers of regions with high
DM densities. -- Populations of dIrr galaxies
are generally pretty simple.
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But, in fact, we do see both the clusters and
the field stars -- Clusters are misleading
regarding SF and chemical evolution.
LMC -- Clusters are not too interesting and
are observed only because they appear to
be easily-picked, low-hanging fruit.
. . . not so fast!
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Instead . . . GCs may reveal a range in star
formation modes and processes over the
lifetimes of dwarf systems -- SN can be
enormous in individual dwarfs (For 28
Sgr 15 WLM 2-4) A threshold effect?
A sign of earlier mergers? Fornax
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Fornax Coleman, Da Costa, Olszewski et
al.
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-- SN also appears to vary in different
regions M31, M81, Scl Why? What drives
cluster formation? Mergers? As in MW
halo? Early conditions when (most)
clusters formed? -- Clusters reveal a
range in SF processes.
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• An illustration (four classes of dwarf SF)
• SFR 0 No gas, no stars or GCs forming
• (dSph)
• SFR low Gas present (maybe lots),
• 0.001-0.01 isolated systems stars form
• but no GCs (dIrr)
• SFR high Stars form in bursts harrass-
• 0.01-1 ment conditions? No
  clusters.
• SFR extr Systemsgas merging? Field
• gt 1 stars form clusters form.

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• Open Issues
• Why can 106-107 Msol of baryons
• decide to form a DG vs a GC? Why
• cant larger systems form in the absence
• of DM?
• Why do certain 107-108 Msol DG choose
• to contain GCs, while others do not?
• Why do 1 km/s and 7 km/s regimes occur
• at early times and close proximity?

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1. Korm plot, SDSS plot, Fornax 2. LeoI plots (dV
vs PA and rot signal) 4. Fornax, N6822, WLM,
SBvsL 6. Images of M81 dwarfsGC, Virgo, M31 7.
Photoshop of For with no stars! 8. Histo of vels
for For clusters/star vels. 9. Histo of ForSgr
GC ages and Fe/H 13. Examples of a) dsph, b)
dirr, c) bursty system IZw18 IC10?, d)
extreme dwarf ? Calculate dispersion
Age, Z, V histos
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