Probing Reionization-Era Galaxies with JWST UV Luminosity Functions and Large-Scale Clustering

Abstract

JWST has transformed our understanding of early galaxy formation, providing an unprecedented view of the first billion years of cosmic history. In this work, we build upon our previously developed semi-analytical framework that self-consistently models the evolving UVLF of galaxies and the global reionization history while incorporating the effects of radiative feedback. Comparing our predictions with JWST and HST data, we identify a fundamental tension: models that match the UVLF fail to reproduce the observed evolution of galaxy clustering (bias) with redshift, and vice versa. To resolve this, we introduce a redshift- and mass-dependent duty cycle linked to the duration of star formation. This duty cycle increases towards higher redshifts, requiring either an enhanced production of UV radiation or increased star formation efficiency at z>10 to match the JWST UVLFs, but declines at lower redshifts (5<z<=9) and towards low-mass halos to remain consistent with the bias and HST UVLF measurements. Reconciling theory with observations requires the characteristic star formation timescale to be longer in massive halos, and to decrease with redshift at fixed halo mass, evolving from ~ 85 Myr at z=6 to ~ 45 Myr at z=14 for $10^{10} M_\odot$ halos. Finally, our extended model, assuming a halo mass-dependent escaping ionizing efficiency ($\varepsilon_{\rm esc} \equiv f_{\rm esc} \times \xi_{\rm ion}$), whose population-averaged value gradually increases with redshift and corresponds to $\langle f_{\rm esc} \rangle \sim$ 15% at z=5 for a fixed value of $\xi_{\rm ion} = 10^{25.23}$ erg$^{-1}$ Hz across all galaxies, produces a reionization history consistent with current constraints. These findings underscore the importance of jointly constraining high-redshift galaxy models using both UVLF and bias statistics to accurately interpret JWST data and refine our understanding of early cosmic evolution.