Globular Cluters in Dwarf Galaxies But first a
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: Fornax Cluster 2 3 4 5 Vh 52. 1 60. 4 47. 4 62. 0 1 deg
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, s. GC = 6. 0 km/s MGC/M* ~ 0. 6 but M/L >> 100 Mass distribution: DM not cuspy.
UMi Survival of Fornax and d. E 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 d. Irr 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]
Fornax Coleman, Da Costa, Olszewski et al.
-- SN also appears to vary in different regions: M 31, M 81, 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 (d. Sph) • SFR = low Gas present (maybe lots), 0. 001 -0. 01 isolated systems; stars form but no GCs (d. Irr) • 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, Fornax 2. Leo. I plots (d. V vs PA and rot signal) 4. Fornax, N 6822, WLM, SBvs. L 6. Images of M 81 dwarfs+GC, Virgo, M 31 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 [IZw 18; IC 10? ], d) extreme dwarf [? ] Calculate dispersion; Age, Z, V histos
- Slides: 29