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ABSTRACT JWST has revealed a large population of UV-bright galaxies at $$z\gtrsim 10$$ and possibly overly massive galaxies at $$z\gtrsim 7$$, challenging standard galaxy formation models in the ΛCDM cosmology. We use an empirical galaxy formation model to explore the potential of alleviating these tensions through an Early Dark Energy (EDE) model, originally proposed to solve the Hubble tension. Our benchmark model demonstrates excellent agreement with the UV luminosity functions (UVLFs) at $$4\lesssim z \lesssim 10$$ in both ΛCDM and EDE cosmologies. In the EDE cosmology, the UVLF measurements at $$z\simeq 12$$ based on spectroscopically confirmed galaxies (eight galaxies at $$z\simeq 11\!-\!13.5$$) exhibit no tension with the benchmark model. Photometric constraints at $$12 \lesssim z\lesssim 16$$ can be fully explained within EDE via either moderately increased star-formation efficiencies ($$\epsilon _{\ast}\sim 3\!-\!10\ \hbox{per cent}$$ at $$M_{\rm halo}\sim 10^{10.5}{\, \rm M_\odot }$$) or enhanced UV variabilities ($$\sigma _{\rm UV}\sim 0.8\!-\!1.3$$ mag at $$M_{\rm halo}\sim 10^{10.5}{\, \rm M_\odot }$$) that are within the scatter of hydrodynamical simulation predictions. A similar agreement is difficult to achieve in $$\Lambda$$CDM, especially at $$z\gtrsim 14$$, where the required $$\sigma _{\rm UV}$$ exceeds the maximum value seen in simulations. Furthermore, the implausibly large cosmic stellar mass densities inferred from some JWST observations are no longer in tension with cosmology when the EDE is considered. Our findings highlight EDE as an intriguing unified solution to a fundamental problem in cosmology and the recent tensions raised by JWST observations. Data at the highest redshifts reached by JWST will be crucial for differentiating modified galaxy formation physics from new cosmological physics. 

Abstract The James Webb Space Telescope is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshiftsz≳ 5. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) of 15 AGN candidates selected to be compact, with red continua in the rest-frame optical but with blue slopes in the UV. From NIRCam photometry alone, they could have been dominated by dusty star formation or an AGN. Here we show that the majority of the compact red sources in UNCOVER are dust-reddened AGN: 60% show definitive evidence for broad-line Hαwith a FWHM > 2000 km s⁻¹, 20% of the current data are inconclusive, and 20% are brown dwarf stars. We propose an updated photometric criterion to select redz> 5 AGN that excludes brown dwarfs and is expected to yield >80% AGN. Remarkably, among allz_phot> 5 galaxies with F277W – F444W > 1 in UNCOVER at least 33% are AGN regardless of compactness, climbing to at least 80% AGN for sources with F277W – F444W > 1.6. The confirmed AGN have black hole masses of 10⁷–10⁹M_⊙. While their UV luminosities (−16 >M_UV> −20 AB mag) are low compared to UV-selected AGN at these epochs, consistent with percent-level scattered AGN light or low levels of unobscured star formation, the inferred bolometric luminosities are typical of 10⁷–10⁹M_⊙black holes radiating at ∼10%–40% the Eddington limit. The number densities are surprisingly high at ∼10⁻⁵Mpc⁻³mag⁻¹, 100 times more common than the faintest UV-selected quasars, while accounting for ∼1% of the UV-selected galaxies. While their UV faintness suggests they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth.