Essential physics of early galaxy formation

We present a theoretical model embedding the essential physics of early galaxy formation (z = 5-12) based on the single premise that any galaxy can form stars with a maximal limiting efficiency that provides enough energy to expel all the remaining gas, quenching further star formation. This simple idea is implemented into a merger-tree based semi-analytical model that utilises two mass and redshift-independent parameters to capture the key physics of supernova feedback in ejecting gas from low-mass halos, and tracks the resulting impact on the subsequent growth of more massive systems via halo mergers and gas accretion. Our model shows that: (i) the smallest halos (halo mass Mₕ ≤ 10¹⁰ M_) build up their gas mass by accretion from the intergalactic medium; (ii) the bulk of the gas powering star formation in larger halos (Mₕ ≥ 1011.5 M_) is brought in by merging progenitors; (iii) the faint-end UV luminosity function slope evolves according to α = -1.75 log \,z -0.52. In addition, (iv) the stellar mass-to-light ratio is well fit by the functional form log\, M_* = -0.38 MUV -0.13\, z + 2.4, which we use to build the evolving stellar mass function to compare to observations. We end with a census of the cosmic stellar mass density (SMD) across galaxies with UV magnitudes over the range -23 ≤ MUV ≤ -11 spanning redshifts $5 < z < 12$: (v) while currently detected LBGs contain ≈ 50% (10%) of the total SMD at $z=5$ (8), the JWST will detect up to 25% of the SMD at z 9.5.