Globular Cluters in Dwarf Galaxies

But first, a digression regarding tides... Leo I

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?

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 V h 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 M GC /M * ~ 0.6 but M/L >> 100 Mass distribution: DM not cuspy.

UMi Survival of Fornax and dE GCs imply cored DM halos to avoid Dyn Friction nucleation.

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 -- S N can be enormous in individual dwarfs (For = 28; Sgr ~ 15; WLM = 2-4) A threshold effect? A sign of earlier mergers? [Fornax]

Fornax Coleman, 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), isolated systems; stars form but no GCs (dIrr) SFR = high Stars form in bursts; harrass ment conditions? No clusters. SFR = extr Systems+gas merging? Field > 1 stars form; clusters form.

Open Issues: Why can 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 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, Fornax 2. LeoI plots (dV vs PA and rot signal) 4. Fornax, N6822, WLM, SBvsL 6. Images of M81 dwarfs+GC, Virgo, M31 7. 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