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Abstract Little Red Dots (LRDs), among the most enigmatic high-redshift discoveries by JWST, are commonly believed to be powered by accreting supermassive black holes. Here, we explore the possibility that these sources are globular clusters in formation, with rest-frame UV arising from a very young stellar population and rest-frame optical from a short-lived supermassive (>10⁴ M_⊙) star. The spectral profiles of LRDs are broadly consistent with this scenario, though the observed temperatures and bolometric luminosities favor emission reprocessed by optically thick continuum-driven winds not fully captured by current models. The LRDz ∼ 5−7 UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at ${\log }_{10}($ M_*/M_⊙) = 5.3 and an exponential cutoff at high masses, consistent with local globular cluster populations. We estimate the total present-day number density of LRDs formed across all redshifts to be ≈0.3 Mpc⁻³, similar within uncertainties to local globular clusters. The observed LRD redshift range matches the age distribution of metal-poor globular clusters, without current LRD counterparts to the metal-rich population. If LRDs are globular clusters in formation, we predict chemical abundance patterns characteristic of multiple stellar populations, including enhanced He and N, and potential Na–O and Al–Mg anticorrelations. These results offer a local perspective to explore this surprisingly abundant population of distant sources, and a potential new window into extreme stellar astrophysics in the early Universe. 

The Magellanic Stream (MS) is known to contain multiple HI strands and corresponding stellar populations are being discovered. Combining a sample of 17 stars from the H3 (“Hectochelle in the Halo at High Resolution”) survey with 891 stars drawn from the Gaia DR3 catalog, we trace stars along a sub-dominant strand of the MS, as defined by gas content, across 30 on the sky. We find that the corresponding dominant strand at the similar position along the MS is devoid of stars with Galactocentric distance $\lesssim 55$ kpc while the subdominant strand shows a close correspondence to such stars. We conclude that (1) these two Stream strands have different origins, (2) they are likely only close in projection, (3) the subdominant strand is tidal in origin, and (4) the subdominant strand is composed of “disk” material, gas and stars, with a chemical composition that marginally favors it coming from the Small Magellanic Cloud. 

Abstract The detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host active galactic nuclei embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous (L_bol ∼ 10⁴⁵erg s⁻¹) LRD atz= 3.501 behind Abell S1063 (μ ∼ 2), observed with deep JWST/NIRCam and a ∼20 hr (80 hr delensed) NIRSpec G395M spectrum. The data reveal over 40 emission and absorption features, including a rich forest of low-ionization Feiilines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, a signature of Thomson scattering requiringn_e ≳ 10⁸cm⁻³. Adopting this width yieldsM_BH ∼ 10^6.7M_⊙, a factor of 10 lower than Gaussian fits, andλ_Edd ∼ 1.8. Additional diagnostics support the same picture: a pronounced Balmer break (f_ν,4050/f_ν,3670 = 2.0 ± 0.1), enhanced Heiλ7065 andλ10830 with P-Cygni absorption, Bowen-fluorescent Oiλ8446–λ11290 emission requiring Lyβpumping, and 16 Feiilines matching fluorescence models. These features indicate a dense (n ∼ 10⁸cm⁻³), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black hole growth in the early Universe. 

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 We present the discovery of extreme nitrogen enrichment by Wolf Rayet nitrogen (WN) stars in the metal-poor (∼10%Z_⊙), lensed, compact (R_eff ∼ 20 pc) galaxy RXCJ2248 atz= 6.1, revealed by unprecedentedly deep JWST/NIRSpec medium-resolution spectroscopy from the GLIMPSE-D Survey. The exquisite signal-to-noise ratio reveals multiple high-ionization nebular lines and broad Balmer and [Oiii] components (FWHM ∼700–3000 km s⁻¹). We detect broadened Heiiλ1640 andλ4687 (FWHM ∼ 530 km s⁻¹) and strong Niiiλ4642 emission consistent with a population of WN stars, making RXCJ2248 the most distant galaxy with confirmed Wolf Rayet (WR) features to date. We measure the multiphase nebular density across five ions, the direct-method metallicity ( $12+\log (\mathrm{O}/\mathrm{H})=7.753\pm 0.025$ ), and a nonuniform elemental enrichment pattern of extreme N/O enhancement ( $\log (\mathrm{N}/\mathrm{O})=-0.391\pm 0.037$ from N⁺, N⁺², and N⁺³) but suppressed C/O relative to empirical C/N trends. We show that this abundance pattern can be explained by enrichment from a dual-burst with a low WR carbon/WN ratio, as expected at low metallicities. Crucially, these signatures can only arise during a brief, rare evolutionary window shortly after a burst (∼3–6 Myr), when WN stars dominate chemical feedback but before dilution by later yields (e.g., supernovae). The observed frequency of strong N emitters at high−zimplies a ∼50 Myr burst duty cycle, suggesting that N/O outliers may represent a brief but ubiquitous phase in the evolution of highly star-forming early galaxies. The WN detection in RXCJ2248, therefore, provides the first direct evidence of WR-driven nitrogen enrichment in the first billion years of the Universe and a novel timing argument for the bursty star formation cycles that shaped galaxies at cosmic dawn. 

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 Our understanding of the assembly timeline of the Milky Way has been transforming along with the dramatic increase in astrometric and spectroscopic data available over the past several years. Many substructures in chemo-dynamical space have been discovered and identified as the remnants of various galactic mergers. To investigate the timeline of these mergers, we select main-sequence turnoff and subgiant stars (MSTOs) from the H3 survey, finding members in seven metal-poor components of the halo: Gaia-Sausage/Enceladus (GSE), the Helmi Streams, Thamnos, Sequoia, Wukong/LMS-1, Arjuna, and I’itoi. We also select out a metal-poor in situ population to facilitate comparison to the evolution of the Milky Way itself at these early epochs. We fit individual isochrone ages to the MSTOs in each of these substructures and use the resulting age distributions to infer simple star formation histories (SFHs). For GSE, we resolve an extended SFH that truncates ≈10 Gyr ago, as well as a clear age–metallicity relation. From this age distribution and measured SFH we infer that GSE merged with the Milky Way at a time 9.5–10.2 Gyr ago, in agreement with previous estimates. We infer that the other mergers occurred at various times ranging from 9 to 13 Gyr ago, and that the metal-poor in situ Galaxy built up within only a few billion years. These results reinforce the emerging picture that both the disk and halo of the Milky Way experienced a rapid assembly. 

Abstract As observations have yet to constrain the ionizing properties of the faintest (M_UV≳ −16) galaxies, their contribution to cosmic reionization remains unclear. The rest-frame ultraviolet (UV) continuum slope (β) is a powerful diagnostic of stellar populations and one of the few feasible indicators of the escape fraction of ionizing photons (f_esc) for such faint galaxies at high redshift. Leveraging ultradeep JWST/NIRCam GLIMPSE imaging of the strong lensing field Abell S1063, we estimate the UV continuum slopes of 553 galaxies atz> 6 with absolute magnitudes down toM_UV≃ −12.5. We find a modest evolution ofβwith redshift and a flattening in theβ–M_UVrelation such that galaxies fainter thanM_UV∼ −16.5 no longer exhibit the bluest UV slopes. The 136 ultrafaint galaxies withM_UV> −16 are a diverse population encompassing dusty (30%), old (15%), and low-mass (50%) galaxies. We apply the empiricalβ–f_escrelation from local Lyman continuum leakers, finding the meanf_escpeaks at ∼20% atM_UV= −16.5 and declines towards fainter galaxies, while remaining consistent withf_esc= 14% within the uncertainties, in agreement with recent radiative transfer simulations. Incorporating GLIMPSE constraints on the UV luminosity function, ionizing photon production efficiency, and escape fractions produces a reionization history consistent with independent observational constraints. Our results indicate galaxies with anM_UVbetween −18 and −14 supplied ∼60% of the ionizing photons to cosmic reionization, while the lowerf_escof fainter galaxies produces a natural cutoff in the ionizing photon production rate density. 

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 Detecting the first generation of stars, Population III (Pop III), has been a long-standing goal in astrophysics, yet they remain elusive even in the JWST era. Here we present a novel NIRCam-based selection method for Pop III galaxies, and carefully validate it through completeness and contamination simulations. We systematically search ≃ 500 arcmin²across JWST legacy fields for Pop III candidates, including GLIMPSE, which, assisted by gravitational lensing, has produced JWST’s deepest NIRCam imaging thus far. We discover one promising Pop III galaxy candidate (GLIMPSE-16043) at $z=6.50_{-0.24}^{+0.03}$ , a moderately lensed galaxy ( $\mu =2.9_{-0.2}^{+0.1}$ ) with an intrinsic UV magnitude of $M_{\mathrm{UV}}=-15.89_{-0.14}^{+0.12}$ . It exhibits key Pop III features: strong Hαemission (rest-frame EW 2810 ± 550 Å); a Balmer jump; no dust (UV slopeβ = −2.34 ± 0.36); and undetectable metal lines (e.g., [Oiii]; [Oiii]/Hβ < 0.44), implying a gas-phase metallicity ofZ_gas/Z_⊙ < 0.5%. These properties indicate the presence of a nascent, metal-deficient young stellar population (<5 Myr) with a stellar mass of ≃10⁵M_⊙. Intriguingly, this source deviates significantly from the extrapolated UV–metallicity relation derived from recent JWST observations atz= 4–10, consistent with UV enhancement by a top-heavy Pop III initial mass function or the presence of an extremely metal-poor active galactic nucleus. We also derive the first observational constraints on the Pop III UV luminosity function atz ≃ 6–7. The volume density of GLIMPSE-16043 (≈10⁻⁴cMpc⁻³) is in excellent agreement with theoretical predictions, independently reinforcing its plausibility. This study demonstrates the power of our novel NIRCam method to finally reveal distant galaxies even more pristine than the Milky Way’s most metal-poor satellites, thereby promising to bring us closer to the first generation of stars than we have ever been before.