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 $M_h \leq 10^{10} M_\odot$) build up their gas mass by accretion from the
intergalactic medium; (ii) the bulk of the gas powering star formation in
larger halos ($M_h \geq 10^{11.5} M_\odot$) is brought in by merging
progenitors; (iii) the faint-end UV luminosity function slope evolves according
to $\alpha = -1.75 \log \,z -0.52$. In addition, (iv) the stellar mass-to-light
ratio is well fit by the functional form $\log\, M_* = -0.38 M_{UV} -0.13\, z +
2.4$, 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 $-23 \leq M_{UV} \leq -11$
spanning redshifts $5 < z < 12$: (v) while currently detected LBGs contain
$\approx 50$% (10%) of the total SMD at $z=5$ (8), the JWST will detect up to
25% of the SMD at $z \simeq 9.5$.
