Matching JWST UV Luminosity Functions with Refined $Lambda$CDM Halo Models
Saeed Fakhry, Maryam Shiravand, Antonino Del Popolo
arXiv:2510.04709v2 Announce Type: replace
Abstract: The James Webb Space Telescope (JWST) has unveiled a population of unexpectedly massive and luminous galaxies at redshifts $z gtrsim 7$, posing a significant challenge to the standard $Lambda$CDM cosmological paradigm. In this work, we address the tension between early JWST observations of luminous high-redshift galaxies and predictions of the standard $Lambda$CDM model by revisiting the physics of dark matter halo formation. Employing refined halo mass functions derived by Del Popolo textit{et al.} (DP1 and DP2) that incorporate angular momentum, dynamical friction, and redshift-dependent collapse barriers, we demonstrate a significant enhancement in the abundance of massive halos at $z gtrsim 7$ compared to the conventional Sheth-Tormen (ST) formalism. Using a semi-empirical framework linking halo mass to UV luminosity, we show that the DP2 model reproduces the observed UV luminosity functions from $z = 7$ to $14$ with moderate star formation efficiencies, whereas the ST model requires implausibly high efficiencies. Our results suggest that the JWST overabundance problem stems not from new physics beyond $Lambda$CDM, but from oversimplified treatments of gravitational collapse, highlighting the critical role of small-scale dissipative dynamics in early structure formation.arXiv:2510.04709v2 Announce Type: replace
Abstract: The James Webb Space Telescope (JWST) has unveiled a population of unexpectedly massive and luminous galaxies at redshifts $z gtrsim 7$, posing a significant challenge to the standard $Lambda$CDM cosmological paradigm. In this work, we address the tension between early JWST observations of luminous high-redshift galaxies and predictions of the standard $Lambda$CDM model by revisiting the physics of dark matter halo formation. Employing refined halo mass functions derived by Del Popolo textit{et al.} (DP1 and DP2) that incorporate angular momentum, dynamical friction, and redshift-dependent collapse barriers, we demonstrate a significant enhancement in the abundance of massive halos at $z gtrsim 7$ compared to the conventional Sheth-Tormen (ST) formalism. Using a semi-empirical framework linking halo mass to UV luminosity, we show that the DP2 model reproduces the observed UV luminosity functions from $z = 7$ to $14$ with moderate star formation efficiencies, whereas the ST model requires implausibly high efficiencies. Our results suggest that the JWST overabundance problem stems not from new physics beyond $Lambda$CDM, but from oversimplified treatments of gravitational collapse, highlighting the critical role of small-scale dissipative dynamics in early structure formation.