Globular Cluters in Dwarf Galaxies

But first, a digression regarding tides . . .

Leo I

For our purposes at this workshop, dwarfgalaxy baryons consist of:

Field stars and gas:

Clusters:

What would be learn if we considered one of thesecomponents, ignoring the other?

Stars and gas only . . .

This is largely how we consider dwarfs at present:

But what if we consider only the clusters?What would we see?

We would still detect DM halos:

1 deg

Cluster Vh

2 52.1 3 60.4 4 47.4 5 62.0

Fornax

Sgr

We can even say something about the nature of these halos:

Mass: velocity dispersion from clusters. Recall this industry started with N=3.

Fornax: N=4, GC = 6.0 km/s MGC/M* ~ 0.6 but M/L >> 100

Mass distribution: DM not cuspy.

UMi

Survival of Fornaxand dE GCs implycored DM halos to avoid Dyn Frictionnucleation.

The GCs alone also reveal a range in

SF history and metallicity. . .

. . . albeit a somewhat less interesting

picture than the field stars reveal.

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.

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!

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]

FornaxColeman, Da Costa,Olszewski et al.

-- 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.

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 Systems+gas merging? Field > 1 stars form; clusters form.

Open Issues:

• Why can 106-107 Msol of baryons decide to form a DG vs a GC? Why can’t 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?

1. Korm plot, SDSS plot, Fornax2. LeoI plots (dV vs PA and rot signal)4. Fornax, N6822, WLM, SBvsL6. Images of M81 dwarfs+GC, Virgo, M317. Photoshop of For with no stars!8. Histo of vels for For clusters/star vels.9. Histo of For+Sgr 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