The mid-infrared (mid-IR) spectrum in galaxies has a long history as a valuable proxy for the dust-obscured component of the star formation rate (SFR) in massive galaxies. In this work, we exploit the capabilities of the James Webb Space Telescopes (JWST) to expand our understanding of the mid-IR and its use in measuring SFRs, covering four orders of magnitude in total infrared luminosity (9≲ log L_ IR/L_⊙≲13). First, using a Main Sequence sample at 1<z<1.75 from SMILES, we calibrate mid-IR-based SFRs against the P_ aα emission line - a gold standard SFR indicator - from the FRESCO survey. We find that the rest-frame ∼6-8 μm emission - dominated by PAHs and probed by the Mid-Infrared Instrument (MIRI) at z∼1.3 - has a superlinear relation with SFR_ P_aα below ∼8 M_⊙ yr^-1, in sharp contrast with the unity relation in more massive galaxies. We derive SFR calibrations for MIRI photometry, finding that a single, representative IR template improves the scatter. We additionally calibrate a UV+IR composite indicator, assuming energy balance, which does return a unity relation, with low scatter. Our examination of the mid-IR in our MS sample indicates that it is tracking the global obscuration fraction, making it a robust proxy for SFR down to our low mass end, log M_⋆/M_⊙∼9, and across the redshift range where MIRI probes the PAHs (0.3≲ z≲3). Finally, we examine the bright end not represented in SMILES, comparing the behavior of local and cosmic noon ultra luminous infrared galaxies to show that the robustness of using the IR as a SFR proxy extends from the faint to bright regimes.

The nature of little red dots (LRDs) has largely been investigated through their continuum emission, with lines assumed to arise from a broad-line region. In this paper, we instead use recombination lines to infer the intrinsic properties of the central engine. Our analysis first reveals a tension between the ionizing properties implied from H alpha and He ii lambda 4686. The high H alpha EWs require copious H-ionizing photons, more than the bluest active galactic nucleus (AGN) ionizing spectra can provide. In contrast, He ii emission is marginally detected, and its low EW is, at most, consistent with the softest AGN spectra. The low He ii/H beta (similar to 10(-2), <20 & times; local AGN median) further points to an unusually soft ionizing spectrum. We extend our analysis to dense gas envelopes (quasi-star/black-hole star) and find that hydrogen recombination lines become optically thick and lose diagnostic power, but He ii remains optically thin and a robust tracer. Photoionization modeling with Cloudy rules out standard AGN accretion disk spectra. Alternative explanations include exotic AGN with red rest-optical emission, high average optical depth (>10) from gas/dust, and soft ionizing spectra with abundant H-ionizing photons, consistent with, e.g., a cold accretion disk or a composite of AGN and stars. The latter is an intriguing scenario since high hydrogen densities are highly conducive for star formation, and nuclear star clusters are found in the vicinity of local massive black holes. While previous studies have mostly focused on features dominated by the absorbing hydrogen cloud, the He ii-based diagnostic proposed here represents a crucial step toward understanding the central engine of LRDs.

JWST has revealed a stunning population of bright galaxies at surprisingly early epochs, z>10, where few such sources were expected. Here we present the most distant example of this class yet – MoM-z14, a luminous (M_UV=-20.2) source in the COSMOS field at z_spec=14.44^+0.02_-0.02 that expands the observational frontier to a mere 280 million years after the Big Bang. The redshift is confirmed with NIRSpec/PRISM spectroscopy through a sharp Lyman-α break and ∼3σ detections of five rest-UV emission lines. The number density of bright z_spec∼14-15 sources implied by our "Mirage or Miracle" survey spanning ∼350 arcmin^2 is >100× larger (182^+329_-105×) than pre-JWST consensus models. The high EWs of UV lines (∼15-35 Å) signal a rising star-formation history, with a ∼10× increase in the last 5 Myr (SFR_5Myr/SFR_50Myr=9.9^+3.0_-5.8). The source is extremely compact (circularized r_e = 74^+15_-12 pc), and yet elongated (b/a=0.25^+0.11_-0.06), suggesting an AGN is not the dominant source of UV light. The steep UV slope (β=-2.5^+0.2_-0.2) implies negligible dust attenuation and a young stellar population. The absence of a strong damping wing provides tentative evidence that the immediate surroundings of MoM-z14 may be partially ionized at a redshift where virtually every reionization model predicts a ∼100% neutral fraction. The nitrogen emission and highly super-solar [N/C]>1 hint at an abundance pattern similar to local globular clusters that may have once hosted luminous supermassive stars. Since this abundance pattern is also common among the most ancient stars born in the Milky Way, we may be directly witnessing the formation of such stars in dense clusters, connecting galaxy evolution across the entire sweep of cosmic time.

While the size-mass relation provides insight into the structural evolution of galaxies, the data available and methods employed have hindered our ability to study a detailed and comprehensive description of this key relation across cosmic history. The first paper in this series presents a morphology catalog based on 20 band JWST data in the field of Abell 2744. In this paper we utilize this catalog to measure the size-mass relation from 0.510, we discuss three distinct phases: Rapid growth at z>5, growth that mimics dark matter halos at 5< z <1 and a late plateau at 0.51. Our results imply that quiescent galaxies are smaller than their star-forming counterparts only at around log M_*/M_⊙ = 10; the two populations have similar sizes at lower and higher masses.

We present the Blue Jay survey, a cycle 1 JWST program aimed at studying the stellar and gas content of galaxies at cosmic noon. The survey consists of deep spectroscopy for 153 targets observed over two pointings in the COSMOS field using the NIRSpec micro-shutter assembly (MSA). We employed the three medium-resolution gratings, G140M, G235M, and G395M, with exposure times of 13 hours, 3.2 hours, and 1.6 hours, respectively. We thus obtained full coverage of the 1 - 5 m range, corresponding to the entire rest-frame optical wavelength range, with a spectral resolution R M_⊙ to 10^ Parallel observations provided deep multiband NIRCam imaging, which partially overlaps with the spectroscopic observations. The sample was carefully selected to provide a census of galaxies over the redshift range 1.7 < z < 3.5 above a redshift-dependent minimum stellar mass that ranges from 10^ 8.7 9.3 M_⊙. The selection ensured that the Blue Jay sample is representative of the entire galaxy population at these redshifts, without strong biases in color, star formation rate, or other properties. The sizes of massive galaxies at these redshifts are comparable to or larger than the NIRSpec shutters, which requires custom strategies for designing and reducing the observations. Since the standard A-B nod subtraction leads to flux self-subtraction for large galaxies, we constructed a master background from empty shutters and subtracted it from each of the science spectra. This in turn allowed us to use shorter slitlets consisting of only two shutters per galaxy instead of the usual three, with a substantial increase in the multiplexing of the NIRSpec MSA. In order to obtain self-consistent fits of spectroscopic and photometric data, we measured multiband photometry using space-based observations from the exact area in the sky where the NIRSpec 1D spectrum is extracted. The spectra contain a wealth of emission and absorption lines, including hydrogen lines (Balmer and Paschen series), helium lines, metal emission lines from ionized gas, metal stellar absorption lines, and resonant absorption lines that can be used to study neutral gas (Na I D and Ca II H, K). Spectroscopic redshifts are unambiguously measured for 93% of the sample. The Blue Jay dataset, which we publicly release, represents the ideal sample for studying the stellar populations, neutral gas, and ionized gas in cosmic noon galaxies, including star formation histories, quenching, outflows, metallicity, and dust attenuation.

We present the UV-to-near-IR (NIR) size evolution of a sample of 161 quiescent galaxies with M-* > 10(10)M(circle dot)over 0.5 < z < 5. With deep multiband NIRCam images in GOODS-South from JADES, we measure the effective radii (R-e) of the galaxies at rest-frame 0.3, 0.5, and 1 mu m. On average, we find that quiescent galaxies are 45% (15%) more compact at rest-frame 1 mu m than they are at 0.3 mu m (0.5 mu m). Regardless of wavelengths, the R-e of quiescent galaxies strongly evolves with redshift, and this evolution depends on stellar mass. For lower-mass quiescent galaxies with M-* = 10(10)-10(10.6)M(circle dot), the evolution follows R-e proportional to (1 + z)(-1.1), whereas it becomes steeper, following R-e proportional to (1 + z)(-1.7), for higher-mass quiescent galaxies with M-* > 10(10.6)M(circle dot). To constrain the physical mechanisms driving the apparent size evolution, we study the relationship between R-e and the formation redshift (z(form)) of quiescent galaxies. For lower-mass quiescent galaxies, this relationship is broadly consistent with R-e proportional to(1+z(form))(-1) , in line with the expectation of the progenitor effect. For higher-mass quiescent galaxies, the relationship between R-e and z(form) depends on stellar age. Older quiescent galaxies have a steeper relationship between R-e and z(form) than that expected from the progenitor effect alone, suggesting that mergers and/or post-quenching continuous gas accretion drive additional size growth in very massive systems. We find that the z > 3 quiescent galaxies in our sample are very compact, with mass surface densities Sigma(e) greater than or similar to 10(10)M(circle dot) kpc(-2), and their R-e are possibly even smaller than anticipated from the size evolution measured for lower-redshift quiescent galaxies. Finally, we take a close look at the structure of GS-9209, one of the earliest confirmed massive quiescent galaxies at z(spec) similar to 4.7. From UV to NIR, GS-9209 becomes increasingly compact, and its light profile becomes more spheroidal, showing that the color gradient is already present in this earliest massive quiescent galaxy.

Little Red Dots (LRDs) are a recently identified population of high-redshift sources, with a common interpretation being accreting black holes embedded within a spherical, optically thick gas envelope. Within this framework, some models propose that the continuum arises from the dense-gas envelope, where hard ionizing radiation from the central engine is reprocessed into a stellar-like photosphere with an effective temperature of ∼5000 K. This implies that both the UV continuum and narrow-line emission are then powered by the host galaxy rather than an exposed central engine. To test whether this is consistent with the observed narrow-line ratios, we analyze multiple line diagnostics for a sample of ∼20 LRDs with high signal-to-noise NIRSpec grating spectra. We find that at least 40% of the LRDs have line ratios pointing toward high ionization parameter and electron temperature, with a further 15% also falling in the AGN regime for the Oi/Hα diagnostic, indicative of harder ionizing radiation. These line ratios are incompatible with stellar photoionization from a star-forming host alone. This suggests lower density channels within the gas envelope through which high energy photons can escape and excite the surrounding narrow-line emitting gas. At the same time, most LRDs lack strong high-ionization line emission, with He ii/Hβ ≲0.1, consistent with an ionizing spectrum softer than that of a standard AGN. Together, these results disfavour a uniform gas envelope with a covering fraction of unity, and instead point to a more complex geometry that gives rise to anisotropic ionizing radiation.

We present an overview of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES), an ambitious program of infrared imaging and spectroscopy in the GOODS-S and GOODS-N deep fields, designed to study galaxy evolution from high redshift to cosmic noon. JADES uses about 770 hours of Cycle 1 guaranteed time largely from the Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec) instrument teams. In GOODS-S, in and around the Hubble Ultra Deep Field and Chandra Deep Field South, JADES produces a deep imaging region of ~45 arcmin$^2$ with an average of 130 hrs of exposure time spread over 9 NIRCam filters. This is extended at medium depth in GOODS-S and GOODS-N with NIRCam imaging of ~175 arcmin$^2$ with an average exposure time of 20 hrs spread over 8-10 filters. In both fields, we conduct extensive NIRSpec multi-object spectroscopy, including 2 deep pointings of 55 hrs exposure time, 14 medium pointings of ~12 hrs, and 15 shallower pointings of ~4 hrs, targeting over 5000 HST and JWST-detected faint sources with 5 low, medium, and high-resolution dispersers covering 0.6-5.3 microns. Finally, JADES extends redward via coordinated parallels with the JWST Mid-Infrared Instrument (MIRI), featuring ~9 arcmin$^2$ with 43 hours of exposure at 7.7 microns and twice that area with 2-6.5 hours of exposure at 12.8 microns For nearly 30 years, the GOODS-S and GOODS-N fields have been developed as the premier deep fields on the sky; JADES is now providing a compelling start on the JWST legacy in these fields.

Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of ancient clusters are challenging due to the age-metallicity degeneracy. Here, we report the discovery of 36 compact stellar systems within the 'Relic', a massive, quiescent galaxy at z=2.53. The Relic resides in an overdensity behind the Abell 2744 cluster, with a prominent tidal tail extending towards two low-mass companions. Using deep data from the UNCOVER/MegaScience JWST Surveys, we find that clusters formed in age intervals ranging from 8 Myr up to ∼2 Gyr, suggesting a rich formation history starting at z∼10. While the cluster-based star formation history is broadly consistent with the high past star formation rates derived from the diffuse host galaxy light, one potential discrepancy is a tentative ∼2-3× higher rate in the cluster population for the past Gyr. Taken together with the spatial distribution and low inferred metallicities of these young-to-intermediate age clusters, we may be seeing direct evidence for the accretion of star clusters in addition to their early in situ formation. The cluster masses are high, ∼10^6-10^7 M_⊙, which may explain why we are able to detect them around this likely post-merger galaxy. Overall, the Relic clusters are consistent with being precursors of the most-massive present-day GCs. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly.

We present spectrally-resolved structural parameter measurements of 29,608 sources from the legacy lensing field of Abell 2744, quantifying global structures from observed 0.7 μm - 4.8 μm and spanning rest-frame UV to NIR at R∼15. These measurements are made on imaging mosaics mainly from the UNCOVER/MegaScience survey, including 20 JWST NIRCam broad and medium bands. We perform single-component Sérsic fitting to these galaxies using , a Bayesian structural fitting tool, to infer their structural parameters and associated random uncertainties from the posterior distributions. Through various quality evaluation criteria, we infer robust structural parameters among > 90% of the selected SNR>10 sources. For each galaxy with reliable sizes in at least two bands and a high-quality redshift, we fit its observed size as a function of wavelength and infer rest-frame UV, optical, and near-infrared sizes where applicable. By performing injection-recovery tests on simulated galaxy cutouts in selected bands, we establish that our structural parameter measurements achieve fractional error < 10 -20% above SNR>10. With this paper, all raw structural measurements and fitted rest-frame sizes are quality-flagged, cataloged, and released to the community. Finally, we demonstrate that this catalog enables the structural study of galaxies over an unprecedentedly wide parameter space of redshift (0.3

We present James Web Space Telescope/NIRSpec dense-shutter spectroscopy (DSS). This novel observing strategy with the NIRSpec/multi-shutter assembly (MSA) deliberately permits a high number of controlled spectral overlaps to reach extreme multiplex while retaining the low background of slit spectroscopy. In a single configuration over the JADES Origins Field, we opened shutters on all faint (m(F444W) < 30 mag) z(phot) > 3 candidates, prioritizing emission-line science and rejecting only bright continuum sources. Using 33.6 and 35.8 ks on-source in G235M and G395M, we observed a single mask with '850 sources, obtaining spectroscopic redshifts for '540 galaxies over 2.5 less than or similar to z less than or similar to 8.9. The per-configuration target density in DSS mode is 4-5 x higher than standard no-and low-overlap MSA strategies ( < 200 sources), with no loss in redshift precision or accuracy. Line-flux sensitivities are 30 per cent lower at fixed exposure time, matching the expected increase in background noise, but the gain in survey speed is 5 x in our setup, more than justifying the penalty. The measured line sensitivity exceeds NIRCam slitless spectroscopy by at least similar to 5 x (similar to 25 x in exposure time) at lambda similar to 4 mu m, demonstrating that DSS is a compelling method to gain deep, wide-band spectra for large samples. Crucially, NIRSpec/MSA could deliver even higher target allocation densities than those used here. We derive H alpha-based star-formation rates, gas-phase metallicities (including a large sample suitable for strong-line calibrations), and identify rare mini-quenched galaxies and broad-line AGN. DSS is immediately applicable wherever deep imaging enables robust pre-selection and astrometry, providing an efficient method to obtain large samples of faint emission-line galaxies, a compelling middle ground between the completeness of slitless surveys and the sensitivity and bandwidth of NIRSpec/MSA.

We present a 'Little Red Dot' (LRD) broad-line active galactic nucleus (AGN) at z = 5.077 observed with NIRSpec/MSA (micro-shutter assembly) and NIRSpec/IFU (integral-field unit) by the JADES (JWST Advanced Deep Extragalactic Survey) and BlackTHUNDER (Black holes in THe early Universe aNd their DensE surRoundings) surveys. Combining spatially resolved and high-resolution spectroscopy, we characterize its central engine, host, and environment. Ho has multiple components, including two broad Gaussians, yielding a black-hole mass log(M-center dot/M-circle dot) = 7.65, while [O III]lambda 5007 gives a galaxy dynamical mass log(M-dyn/M-circle dot) 9.1, suggesting an overmassive black hole relative to the host galaxy. The target is immersed in a 7-kpc wide pool of ionized gas and has three neighbours: a satellite galaxy, a possible satellite/gas cloud, and a tentatively detected spatially detached outflow. Hoa shows strong, rest-frame absorption, deeper than the continuum, ruling out a stellar origin. The velocity and velocity dispersion are V-ahs-13 km s(-1) and sigma(abs) = 120 km s(-1). There is tentative evidence (2.6 sigma) of temporal variability in the equivalent width of the Hot absorber over two rest-frame months, suggesting a highly dynamic nucleus. Notably, while the Ha absorber is clearly visible and even dominant in the high-resolution G395H observations, it is not detected in the medium-resolution G395M data of the same epoch. This implies that the current incidence rate of absorbers in LRDs - and especially of rest-frame absorbers - may be severely underestimated, because most LRDs rely on lower resolution spectroscopy. The high incidence rate of rest-frame absorbers in LRDs may indicate a configuration that is either intrinsically stationary, such as a rotating disc, or that exhibits time-averaged stability, such as an oscillatory "breathing mode' accretion with cyclic expansion and contraction of the gas around the supermassive black hole.

The James Webb Space Telescope (JWST) is unveiling the rest-frame near-IR structure of galaxies. We measure the evolution with redshift of the rest-frame optical and near-IR Sérsic index (n), and examine the dependence on stellar mass and star-formation activity across the redshift range 0.5≤ z≤2.5. We infer rest-frame near-IR Sérsic profiles for ≈ 15.000 galaxies in publicly available NIRCam imaging mosaics from the COSMOS-Web and PRIMER surveys. We augment these with rest-frame optical Sérsic indices, previously measured from HST imaging mosaics. The median Sérsic index evolves slowly or not at all with redshift, except for very high-mass galaxies (M_⋆ > 10^11 M_⊙), which show an increase from n≈ 2.5 to n≈ 4 at z<1. High-mass galaxies have higher n than lower-mass galaxies (M_⋆=10^9.5 M_⊙) at all redshifts, with a stronger dependence in the rest-frame near-IR than in the rest-frame optical at z>1. This wavelength dependence is caused by star-forming galaxies that have lower optical than near-IR n at z>1 (but not at z<1). Both at optical and near-IR wavelengths, star-forming galaxies have lower n than quiescent galaxies, fortifying the connection between star-formation activity and radial stellar mass distribution. At z>1 the median near-IR n varies strongly with star formation activity, but not with stellar mass. The scatter in near-IR n is higher in the green valley (0.25 dex) than on the star-forming sequence and among quiescent galaxies (0.18 dex) – this trend is not seen in the optical because dust and young stars contribute to the variety in optical light profiles. Our newly measured rest-frame near-IR radial light profiles motivate future comparisons with radial stellar mass profiles of simulated galaxies as a stringent constraint on processes that govern galaxy formation.

JWST has revealed a population of 'Little Red Dots' (LRDs): compact, red objects at redshifts z=2-9 with 'v'-shaped spectral energy distributions, broad permitted lines, and, often, hydrogen Balmer absorption. We use NIRSpec/IFS data from the BlackTHUNDER survey to study the Hα line in the LRD Abell2744-QSO1 at z=7.04, which is a confirmed AGN due to time-variable equivalent width (EW) in its broad emission lines. The Hα spectral profile is non-Gaussian, requiring at least two Gaussian components. We also detect a narrow-line Gaussian component, and strong Hα absorption (EW relative to the continuum ∼ 22_-7^+12A), confirming a connection between the strong Balmer break and line absorption. The absorber is at rest with respect to broad Hα, suggesting that the gas cannot be interpreted as an inflow or outflow, forming instead a long-lived structure. Its velocity dispersion is σ_ abs=110_-10^+20 km s^-1, consistent with the value inferred from the analysis of the Balmer break. Based on Hα, we infer a black hole mass of log(M_ BH/ M_⊙)=7.2, smaller but close to the previous estimates based on Hβ. The Eddington ratio is 0.09. Combining the high signal-to-noise ratio of the narrow Hα line with the spectral resolution R=3,700 of the G395H grating, we infer a narrow-line intrinsic dispersion σ_ n=22_-6^+5 km s^-1, which places a stringent constraint on the black-hole-to-dynamical-mass ratio of this system to be M_ BH/M_ dyn=0.15-1.2, confirming the overmassive nature of the black hole and potentially leaving little room for a host galaxy.

We present a broad-line active galactic nucleus (AGN) at z = 5.077, observed with both NIRSpec/MSA and NIRSpec/IFU by the JADES and BlackTHUNDER surveys. The target exhibits all the hallmark features of a 'Little Red Dot' (LRD) AGN. The combination of spatially resolved and high-resolution spectroscopy offers deeper insight into its nature. The Hα line has multiple components, including two broad Gaussians, yielding a black-hole mass of log(M_ BH/M_⊙) = 7.65, while the narrow [O III]λ5007 gives a galaxy dynamical mass of log(M_ dyn/M_⊙) = 9.1, suggesting a dynamically overmassive black hole relative to the host galaxy. The target has two satellites, and is immersed in a 7-kpc wide pool of ionized gas. A spatially detached outflow is also tentatively detected. Hα shows strong absorption with high equivalent width (EW), ruling out a stellar origin, and with velocity and velocity dispersion of v = -13 km s^-1 and σ = 120 km s^-1. There is tentative evidence (2.6 σ) of temporal variability in the EW of the Hα absorber over two rest-frame months. If confirmed, this would suggest a highly dynamic environment. Notably, while the Hα absorber is clearly visible and even dominant in the high-resolution G395H observations, it is not detected in the medium-resolution G395M data of the same epoch. This implies that the current incidence rate of absorbers in LRDs - and especially of rest-frame absorbers - may be severely underestimated, because most LRDs rely on lower-resolution spectroscopy. In this context, the high incidence rate of rest-frame absorbers in LRDs may indicate a configuration that is either intrinsically stationary, such as a rotating disc, or that exhibits time-averaged stability, such as an oscillatory 'breathing mode' accretion of cyclic expansion and contraction of the gas around the SMBH.

We present an overview of the MINERVA survey, a 259.8 hour (prime) and 127 hour (parallel) Cycle 4 treasury program on the James Webb Space Telescope (JWST). MINERVA is obtaining 8 filter NIRCam medium band imaging (F140M, F162M, F182M, F210M, F250M, F300M, F360M, F460M) and 2 filter MIRI imaging (F1280W, F1500W) in four of the five CANDELS Extragalactic fields: UDS, COSMOS, AEGIS and GOODS-N. These fields were previously observed in Cycle 1 with 7 - 9 NIRCam filters by the PRIMER, CEERS and JADES programs. MINERVA reaches a 5σ depth of 28.1 mag in F300M and covers ∼ 542 arcmin^2, increasing the area of existing JWST medium-band coverage in at least 8 bands by ∼ 7×. The MIRI imaging reaches a 5σ depth of 23.9 mag in F1280W and covers ∼ 275 arcmin^2 in at least 2 MIRI filters. When combined with existing imaging, these data will provide a photometric catalog with 20-26 JWST filters (depending on field) and 26-35 filters total, including HST. This paper presents a detailed breakdown of the filter coverage, exposure times, and field layout relative to previous observations, as well as an overview of the primary science goals of the project. These include uncovering the physics of enigmatic sources hiding in current broadband catalogs, improving systematics on stellar mass functions and number densities by factors of ≳ 3, and resolved mapping of stellar mass and star formation at 1 < z < 6. When complete, MINERVA will become an integral part of the treasury deep field imaging datasets, significantly improving population studies with well-understood completeness, robust photometric redshifts, stellar masses, and sizes, and facilitating spectroscopic follow up for decades to come.

We report the detection of a 13$\sigma$ H$\alpha$ emission line from HDF850.1 at $z=5.188\pm0.001$ using the FRESCO NIRCam F444W grism observations. Detection of H$\alpha$ in HDF850.1 is noteworthy, given its high far-IR luminosity, substantial dust obscuration, and the historical challenges in deriving its redshift. HDF850.1 shows a clear detection in the F444W imaging data, distributed between a northern and southern component, mirroring that seen in [CII] from the Plateau de Bure Interferometer. Modeling the SED of each component separately, we find that the northern component has a higher mass, star formation rate (SFR), and dust extinction than the southern component. The observed H$\alpha$ emission appears to arise entirely from the less-obscured southern component and shows a similar $\Delta$v$\sim$+130 km/s velocity offset to that seen for [CII] relative to the source systemic redshift. Leveraging H$\alpha$-derived redshifts from FRESCO observations, we find that HDF850.1 is forming in one of the richest environments identified to date at $z>5$, with 100 $z=5.17-5.20$ galaxies distributed across 10 structures and a $\sim$(15 cMpc)$^3$ volume. Based on the evolution of analogous structures in cosmological simulations, the $z=5.17-5.20$ structures seem likely to collapse into a single $>$10$^{14}$ $M_{\odot}$ cluster by $z\sim0$. Comparing galaxy properties forming within this overdensity with those outside, we find the masses, SFRs, and $UV$ luminosities inside the overdensity to be clearly higher. The prominence of H$\alpha$ line emission from HDF850.1 and other known highly-obscured $z>5$ galaxies illustrates the potential of NIRCam-grism programs to map both the early build-up of IR-luminous galaxies and overdense structures.

Environmental quenching—where interactions with other galaxies and/or the intracluster medium suppress star formation in low-mass galaxies—has been well established as the primary driver behind the formation of the red sequence for low-mass galaxies within clusters at low redshift ( z < 1). However, it remains unclear whether these mechanisms are active at higher redshifts in protocluster environments that are not yet fully virialized. In large part, this regime has remained unexplored due to observational limitations; however, JWST has recently opened a new window into the role of environmental quenching on low-mass (log( M _⋆ / M _⊙ ) < 9.0) galaxies at cosmic noon (2 < z < 3). Here, we leverage the deep imaging and R ∼ 15 spectrophotometry enabled by the 20 band JWST/NIRCam data from the UNCOVER and MegaScience programs to examine environmental quenching in a newly discovered z ≈ 2.58 protocluster. We compare the star formation histories of 19 low-mass quiescent galaxies in the protocluster to a matched sample of 18 in the field and find no significant differences. This similarity extends to galaxy sizes and quenched fractions, which also show no significant differences between the two environments across the full stellar mass range (8.5 < log( M _⋆ / M _⊙ ) ≤ 11.0). This indicates that the protocluster has not yet accelerated quenching relative to the field and is consistent with expectations that z > 2 protoclusters have yet to virialize and develop a dense enough environment required to efficiently quench low-mass galaxies.

The metallicity of galaxies, and its variation with galactocentric radius, provides key insights into the formation histories of galaxies and the physical processes driving their evolution. In this work, we analyze the radial metallicity gradients of star-forming galaxies in the EAGLE, Illustris, IllustrisTNG, and SIMBA cosmological simulations across broad mass (10 ^8.0 M _⊙ ≤ M _⋆ ≲ 10 ^12.0 M _⊙ ) and redshift (0 ≤ z ≤ 8) ranges. We find that all simulations predict strong negative (i.e., radially decreasing) metallicity gradients at early cosmic times, likely due to their similar treatments of relatively smooth stellar feedback not providing sufficient mixing to quickly flatten gradients. The strongest redshift evolution occurs in galaxies with stellar masses of 10 ^10.0 –10 ^11.0 M _⊙ , while galaxies with stellar mass < 10 ^10 M _⊙ and >10 ^11 M _⊙ exhibit weaker redshift evolution. Our result of negative gradients at high redshift contrast with the many positive and flat gradients in the 1 < z < 4 observational literature. At z > 6, the negative gradients observed with JWST and the Atacama Large Millimeter/submillimeter Array are flatter than those in simulations, albeit with closer agreement than at lower redshift. Overall, we suggest that these smooth stellar feedback galaxy simulations may not sufficiently mix their metal content radially, and that either stronger stellar feedback or additional subgrid turbulent metal diffusion models may be required to better reproduce observed metallicity gradients.

JWST has revealed diverse new populations of high-redshift ( z ∼ 4–11) active galactic nuclei (AGNs) and extreme star-forming galaxies that challenge current photoionization models. In this paper, we use rest-frame UV emission-line diagnostics to identify AGN candidates and other exceptional ionizing sources, complementing previous studies predominantly focused on broad-line AGNs. From a parent sample of 205 z _spec > 3 UNCOVER galaxies with NIRSpec/PRISM follow-up, we identify 12 galaxies with C IV , He II , and/or C III ] emission. Three of these galaxies also exhibit clear N III ] and/or N IV ] lines. Leveraging the combined rest-optical and UV coverage of PRISM, we limit the emission-line model space using the sample’s [O III ]/H β distribution, significantly decreasing the overlap between AGN and star formation models in the UV diagnostics. We then find that the five He II emitters are the strongest AGN candidates, with further support from two [Ne v ] detections and one X-ray detection from Chandra. Our Balmer line fits also reveal one new broad-line AGN at z = 6.87. We cannot robustly quantify the AGN fraction in this sample, but we note that close to 20% of M _* > 2 × 10 ^9 M _⊙ parent sample galaxies are AGN candidates. The lower-mass line emitters, which are consistent with both AGN and star-forming photoionization models, have more compact sizes and higher specific star formation rates than the parent sample. Higher-resolution and deeper data on these UV line emitters should provide much stronger constraints on the obscured AGN fraction at z > 3.