Review Article

The First Galaxies and the Likely Discovery of Their Fossils in the Local Group

Figure 5

(a) Average star formation efficiency (i.e., fraction of the collapsed baryon mass converted into stars), (thick curves), and gas fraction (i.e., fraction of the collapsed baryon mass retained in the gas phase) (thin curves), of the first galaxies as a function of their halo mass for run S2 in RGS08 at , and . For comparison, the symbol with error bar shows the expected star formation efficiency (roughly  M divided by the baryonic mass of the halo) in the first mini halo of mass  M simulated by Abel et al. [71]. The dot-dashed line shows a power-law fit for the mean SFE, . The SFE is nearly independent of redshift apart from an increase in halos with  M at . (b) Same as (a) but showing the star formation efficiency, , for individual galaxies in the simulation at . Circles, from smaller to the larger, refer to galaxies with gas fractions % (blue), % (cyan), % (red), and % (green), respectively.