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
Top Related