Essential physics of early galaxy formation

Abstract

We present a theoretical model embedding the essential physics of early\ngalaxy formation (z = 5-12) based on the single premise that any galaxy can\nform stars with a maximal limiting efficiency that provides enough energy to\nexpel all the remaining gas, quenching further star formation. This simple idea\nis implemented into a merger-tree based semi-analytical model that utilises two\nmass and redshift-independent parameters to capture the key physics of\nsupernova feedback in ejecting gas from low-mass halos, and tracks the\nresulting impact on the subsequent growth of more massive systems via halo\nmergers and gas accretion. Our model shows that: (i) the smallest halos (halo\nmass $M_h \\leq 10^{10} M_\\odot$) build up their gas mass by accretion from the\nintergalactic medium; (ii) the bulk of the gas powering star formation in\nlarger halos ($M_h \\geq 10^{11.5} M_\\odot$) is brought in by merging\nprogenitors; (iii) the faint-end UV luminosity function slope evolves according\nto $\\alpha = -1.75 \\log \\,z -0.52$. In addition, (iv) the stellar mass-to-light\nratio is well fit by the functional form $\\log\\, M_* = -0.38 M_{UV} -0.13\\, z +\n2.4$, which we use to build the evolving stellar mass function to compare to\nobservations. We end with a census of the cosmic stellar mass density (SMD)\nacross galaxies with UV magnitudes over the range $-23 \\leq M_{UV} \\leq -11$\nspanning redshifts $5 < z < 12$: (v) while currently detected LBGs contain\n$\\approx 50$% (10%) of the total SMD at $z=5$ (8), the JWST will detect up to\n25% of the SMD at $z \\simeq 9.5$.\n