1. Modeling Star Formation and Chemical Evolution in the Local Group dwarfs Oleg Gnedin University of Michigan

2. Dolphin et al. 2005 and Holtzman et al. 2006
New detailed star formation histories of all classic Local Group dwarfs from archival HST CMDs:
Dolphin et al and Holtzman et al. 2006

3. Star formation histories of dSph and dIrr galaxies are similar
dSph + dE
dIrr + Tr

4. Star formation histories of dSph and dIrr galaxies are indistinguishable without the most recent 2 Gyr

5. Orban, OG, Weisz, Skillman, Dolphin & Holtzman ApJ, 686, 1030 (2008)
Chris Orban (Ohio State) Dan Weisz and Evan Skillman (Minnesota)

6. (figure from Barkana & Loeb 2001)
Primordial gas does not cool efficiently in halos with T < 104 K but we may also need to suppress star formation in larger halos
Vc=10 km/s km/s HI
HeII H2
(figure from Barkana & Loeb 2001)

7. Different M/L relations have been proposed for selected halos to fit the luminosity function. We need complementary data to test the models: star formation histories and metallicities.
SDSS
number of dwarfs vs. velocity (proxy for mass)
within 200 h-1 kpc of each large halo (MW and M31)
Kravtsov, OG, Klypin (2004)

8. 1 Gyr
2 Gyr
5 Gyr
10 Gyr
stellar mass function
mean age

9. Stochastic star formation is required to explain a small subset of relatively young stars (1-2 Gyr)

10. Stochastic star formation threshold allows recent SF
Can determine the amount of variation

11. Example of stochastic star formation: isolated HII regions on the outskirts of spiral galaxies
M83 with GALEX

12. Dynamical Mass within r = 0.3 kpc

13. Photometrically-derived abundances of heavy elements generally agree with those derived spectroscopically
Mateo (2008)

14. Build-up of metallicity is tightly linked to growth of stellar mass  consistent with closed-box chemical evolution