The first galaxies: simulating their feedback-regulated assembly

We investigate the formation of a galaxy reaching a virial mass of ≈10⁸ M_⊙ at z ≈ 10 by carrying out a zoomed radiation-hydrodynamical cosmological simulation. This simulation traces Population III (Pop III) star formation, characterized by a modestly top-heavy initial mass function, and considers stellar feedback such as photoionization heating from Pop III and Population II (Pop II) stars, mechanical and chemical feedback from supernovae (SNe), and X-ray feedback from accreting black holes and high-mass X-ray binaries. We self-consistently impose a transition in star formation mode from top-heavy Pop III to low-mass Pop II, and find that the star formation rate in the computational box is dominated by Pop III until z ∼ 13, and by Pop II thereafter. The simulated galaxy experiences bursty star formation, with a substantially reduced gas content due to photoionization heating from Pop III and Pop II stars, together with SN feedback. All the gas within the simulated galaxy is metal-enriched above 10^-5 Z_⊙, such that there are no remaining pockets of primordial gas. The simulated galaxy has an estimated observed flux of ∼10^-3 nJy, which is too low to be detected by the James Webb Space Telescope without strong lensing amplification. We also show that our simulated galaxy is similar in terms of stellar mass to Segue 2, the least-luminous dwarf known in the Local Group.