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

Figure 8

(a) The gas density, 𝑛_g,core (solid curves), and hydrogen column density, 𝑁_H=2𝑟_c𝑛_g,core (dashed curves), within the core, 𝑟_c, of a minihalo at redshift 𝑧=0 as a function its circular velocity at 𝑟_c. The minimum 𝑣_cir in each curve is determined by the condition 𝑡_rec/𝑡_H<1, necessary for cooling to 𝑇_gas∼10⁴ K. The horizontal lines with arrows show the requirement for cooling to temperatures below 10⁴ K, necessary for initiate star formation, for gas metallicity 𝑍=0.1 (lower line) and 0.01 Z⊙ (higher line). (b) Same as (a) but for minihalos whose gas is able to cool to 𝑇_g,core=5000 K due to metal pre-enrichment (𝑍=0.1 Z⊙). These halos are likely able to sustain a multi-phase ISM and form stars.

(a)

(b)