A Redshift-independent Efficiency Model: Star Formation and Stellar Masses in Dark Matter Halos at z ≳ 4

Abstract

Abstract We explore the connection between the UV luminosity functions (LFs) of high-z galaxies and the distribution of stellar masses and star formation histories (SFHs) in their host dark matter halos. We provide a baseline for a redshift-independent star formation efficiency model to which observations and models can be compared. Our model assigns a star formation rate (SFR) to each dark matter halo based on the growth rate of the halo and a redshift-independent star formation efficiency. The dark matter halo accretion rate is obtained from a high-resolution N-body simulation in order to capture the stochasticity in accretion histories and to obtain spatial information for the distribution of galaxies. The halo mass dependence of the star formation efficiency is calibrated at z = 4 by requiring a match to the observed UV LF at this redshift. The model then correctly predicts the observed UV LF at z = 5–10. We present predictions for the UV luminosity and stellar mass functions, JWST number counts, and SFHs. In particular, we find a stellar-to-halo mass relation at z = 4–10 that scales with halo mass at M h < 1011 M ⊙ as M ⋆ ∝ M h 2, with a normalization that is higher than the relation inferred at z = 0. The average SFRs increase as a function of time to z = 4, although there is significant scatter around the average: about 6% of the z = 4 galaxies show no significant mass growth. Using these SFHs, we present redshift-dependent UV-to-SFR conversion factors, mass return fractions, and mass-to-light ratios for different initial mass functions and metallicities, finding that current estimates of the cosmic SFR density at z ∼ 10 may be overestimated by ∼0.1–0.2 dex.