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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 Neutron star mergers (NSMs) producer-process elements after a time-delayed inspiral process. Once a significant number of NSMs are present in a galaxy,r-process elements, such as Eu, are expected to significantly increase with time. Yet, there have been limited observational data in support of Eu increasing within Local Group galaxies. We have obtained high-resolution Magellan/MIKE observations of 43 metal-poor stars in the Gaia-Sausage/Enceladus (GSE) tidally disrupted galaxy with −2.5 < [Fe/H] < −1. For the first time, we find a clear rise in [Eu/Mg] with increasing [Mg/H] within one galaxy. We use a simple chemical evolution model to study how such a rise can result from the interplay of prompt and delayedr-process enrichment events. Delayedr-process sources are required to explain the rise and subsequent leveling off of [Eu/Mg] in this disrupted galaxy. However, the rise may be explained by delayedr-process sources with either short (∼10 Myr) or long (∼500 Myr) minimum delay times. Future studies on the nature ofr-process sources and their enrichment processes in the GSE will require additional stars in the GSE at even lower metallicities than the present study. 

ABSTRACT Recent observations from the EIGER JWST program have measured for the first time the quasar–galaxy cross-correlation function at $$z\approx 6$$. The autocorrelation function of faint $$z\approx 6$$ quasars was also recently estimated. These measurements provide key insights into the properties of quasars and galaxies at high redshift and their relation with the host dark matter haloes. In this work, we interpret these data building upon an empirical quasar population model that has been applied successfully to quasar clustering and demographic measurements at $$z\approx 2\!-\!4$$. We use a new, large-volume N-body simulation with more than a trillion particles, FLAMINGO-10k, to model quasars and galaxies simultaneously. We successfully reproduce observations of $$z\approx 6$$ quasars and galaxies (i.e. their clustering properties and luminosity functions), and infer key quantities such as their luminosity–halo mass relation, the mass function of their host haloes, and their duty cycle/occupation fraction. Our key findings are (i) quasars reside on average in $$\approx 10^{12.5}\, {\rm M}_{\odot }$$ haloes (corresponding to $$\approx 5\sigma$$ fluctuations in the initial conditions of the linear density field), but the distribution of host halo masses is quite broad; (ii) the duty cycle of (UV-bright) quasar activity is relatively low ($$\approx 1~{{\ \rm per\ cent}}$$); (iii) galaxies (that are bright in [O iii]) live in much smaller haloes ($$\approx 10^{10.9}\, {\rm M}_{\odot }$$) and have a larger duty cycle (occupation fraction) of $$\approx 13~{{\ \rm per\ cent}}$$. Finally, we focus on the inferred properties of quasars and present a homogeneous analysis of their evolution with redshift. The picture that emerges reveals a strong evolution of the host halo mass and duty cycle of quasars at $$z\approx 2\!-\!6$$, and calls for new investigations of the role of quasar activity across cosmic time. 

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.