A comparison of pre-existing ΛCDM predictions with the abundance of JWST galaxies at high redshift

Observations with the James Webb Space Telescope have revealed a high abundance of bright galaxies at redshift, z ≳ 12, which has been widely interpreted as conflicting with the ΛCDM model. In Cowley et al. (2018) predictions were made – prior to the JWST observations – for the expected abundance of these galaxies using the Durham semi-analytic galaxy formation model, galform, which is known to produce a realistic population of galaxies at lower redshifts including the present day. Key to this model is the assumption of a “top-heavy” initial mass function of stars formed in bursts (required to explain the number counts and redshift distribution of sub-millimetre galaxies). Here, we compare the rest-frame ultraviolet luminosity functions derived from JWST observations with those predicted by the Cowley et al. model up to z = 14 and make further predictions for z = 16. We find that below z ∼ 10, the Cowley et al. predictions agree very well with observations, while agreement at z ≳ 12 requires extending the model to take into account the timescale for the growth of obscuring dust grains at these very early times and its dependence on gas metallicity. We trace the evolution of these galaxies from z = 14 to z = 0 and find that their descendants typically reside in halos with a median mass 2.5 × 1013 h−1 M⊙. The stellar masses of the descendants range from 3.2 × 106 h−1 M⊙ to 3.2 × 1011 h−1 M⊙. Although these galaxies were all central galaxies at z = 14, over half of their descendants end up as satellites in massive halos.