High-redshift Galaxies from Early JWST Observations: Constraints on Dark Energy Models

Abstract Early observations with JWST have led to the discovery of an unexpectedly large density (stellar-mass density ρ * ≈ 10 6 M ⊙ Mpc −3 ) of massive galaxies (stellar masses M * ≥ 10 10.5 M ⊙ ) at extremely high redshifts z ≈ 10. While such a result is based on early measurements that are still affected by uncertainties currently under consideration by several observational groups, its confirmation would have a strong impact on cosmology. Here we show that—under the most conservative assumptions and independently of the baryon physics involved in galaxy formation—such galaxy abundance is not only in tension with the standard ΛCDM cosmology but provides extremely tight constraints on the expansion history of the universe and on the growth factors corresponding to a wide class of Dynamical Dark Energy (DDE) models. Adopting a parameterization w = w 0 + w a (1 − a ) for the evolution of the DDE equation of the state parameter w with the expansion factor a , we derive constraints on combinations of ( w 0 , w a ) that rule out with confidence level >2 σ a major portion of the parameter space ( w 0 , w a ) allowed (or even favored) by existing cosmological probes.