A comparison of pre-existing $\hat{I}›$CDM predictions with the abundance of {\it JWST} galaxies at high redshift

Abstract

Observations with the {\it James Webb Space Telescope} have revealed a high abundance of bright galaxies at redshift, $z\gtrsim 12$, which has been widely interpreted as conflicting with the $\hat{I}›$CDM model. In Cowley et al. (2018) predictions were made -- prior to the {\it JWST} observations -- for the expected abundance of these galaxies using the Durham semi-analytic galaxy formation model, {\sc 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 {\it 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 $z\sim 10$, the Cowley et al. predictions agree very well with observations, while agreement at $z\gtrsim 12$ 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 $2.5\times 10^{13}{h}^{-1}{\mathrm{M}}_{\odot }$. The stellar masses of the descendants range from $3.2\times 10^6{h}^{-1}{\mathrm{M}}_{\odot }$ to $3.2\times 10^{11}{h}^{-1}{\mathrm{M}}_{\odot }$. Although these galaxies were all central galaxies at $z=14$, over half of their descendants end up as satellites in massive halos.

16 pages, 11 figures, accepted for publication in MNRAS