Speaker
Description
With JWST revolutionizing our view of the early Universe, theoretical predictions at high redshifts have become more critical than ever. We investigate the evolution of the galaxy stellar mass function (GSMF) and star formation rates (SFRs) across cosmic time using the new COLIBRE simulations of galaxy formation. COLIBRE improves upon the EAGLE model by incorporating a multiphase interstellar medium, computing radiative cooling rates of primordial elements in non-equilibrium, and employing more sophisticated prescriptions for stellar and AGN feedback. We present the GSMF from the COLIBRE simulations at three resolutions: gas particle masses of $\sim 10^7$, $\sim 10^6$, and $\sim 10^5~\mathrm{M_\odot}$ in cosmological volumes of $400^3$, $200^3$, and $50^3~\mathrm{cMpc}^3$, respectively. We demonstrate that COLIBRE reproduces the observed GSMF over the entire redshift range for which there are observations to compare with ($0<z<12$), including recent JWST constraints. In addition, we examine the evolution of the stellar-to-halo mass relation (SHMR), cosmic SFR density (CSFRD), and galaxy quenched fraction. We show that COLIBRE reproduces the CSFRD and the number density of quiescent galaxies at high redshifts reported by JWST, while predicting an SHMR that evolves minimally with redshift. We discuss the physical implications of these findings and the important role of the Eddington bias when comparing simulation predictions to observations. We conclude that neither a redshift-dependent star formation efficiency, nor a deviation from the $\Lambda\mathrm{CDM}$ cosmology, nor a variable initial stellar mass function is necessary to reproduce the high-redshift JWST stellar masses and SFRs.