Larry D. Bradley

We present a spatially resolved analysis of stellar populations in the brightest z > 6 galaxy known to date (AB mag 23), the strongly lensed MACS0308−zD1 (dubbed the “Cosmic Spear”) at z _spec = 6.2. New JWST NIRCam imaging and high-resolution NIRSpec integral field unit (IFU) spectroscopy span the rest-frame ultraviolet to optical. The NIRCam imaging reveals bright star-forming clumps and a tail consisting of three distinct, extremely compact star clusters that are multiply imaged by gravitational lensing. The star clusters have delensed effective radii of R _eff ≲ 8 pc, stellar masses of M _* ∼ 10 ⁶ –10 ⁷ M _⊙ , and high stellar mass surface densities of Σ _* ≳ 2 × 10 ⁴ M _⊙ pc ⁻² . While their stellar populations are very young (∼6–11 Myr), their dynamical ages exceed unity, consistent with the clusters being gravitationally bound systems. Placing the star clusters in the size versus stellar mass density plane, we find they occupy a region similar to other high-redshift star clusters within galaxies observed recently with JWST, being significantly more massive and denser than local star clusters. Spatially resolved analysis of the brightest clump reveals a compact, intensely star-forming core. The ionizing photon production efficiency ( ξ _ion ) is slightly suppressed in this central region, potentially indicating a locally elevated Lyman continuum escape fraction facilitated by feedback-driven channels.

We present the discovery of a strongly lensed galaxy at z ∼ 11–12, dubbed the “Misty Moons,” identified in the JWST Treasury Survey, Vast Exploration for Nascent, Unexplored Sources. The Misty Moons is gravitationally lensed by the galaxy cluster MACS J0257.1-2325 at z = 0.505, and has five multiple images suggested by two independent lens models. Two of the five images, ID1 and ID2 ( μ ∼ 20–30), are very bright (F200W∼26 AB mag) and exhibit blue SEDs with prominent Ly α breaks. In the source plane, the Misty Moons is a sub- L ^* galaxy ( M _UV ∼ −18.0 mag) resolved into multiple stellar clumps, each of which has an effective radius of r _eff ∼ 10–70 pc and a stellar mass of ∼10 ⁷ M _⊙ . These clumps dominate the stellar mass budget of the Misty Moons (≳80%), similar to other high- z clumps, which suggests a highly clustered mode of star formation in the early Universe, unlike seen in local dwarf galaxies. We convolve the source-plane image with the JWST/NIRCam point-spread function to produce a mock NIRCam image of the Misty Moons without lensing magnification and find that the intrinsic galaxy has a radial surface-brightness profile comparable to those of z ≳ 10 faint galaxies, such as JADES-GS-z13-0 and JADES-GS-z14-1, indicating that the Misty Moons represents a typical z ≳ 10 faint galaxy. The Misty Moons, a lensed galaxy with resolved internal structures, provides an ideal laboratory for exploring the early stages of galaxy formation at z ≳ 10.

We present Galaxy Synthesizer ( GalSyn ), a modular and flexible Python package for generating synthetic observations from hydrodynamical galaxy simulations. GalSyn generates synthetic spectrophotometric data cubes for individual galaxies from simulation cutouts, employing a particle-by-particle spectral modeling approach that enables the rapid production of large synthetic datasets required for statistical population studies, offering a computationally efficient alternative to full radiative transfer codes. Users have full control over the spectral modeling choices, including the stellar population synthesis engine, stellar isochrones, spectral libraries, and initial mass functions. Dust attenuation is modeled at spatially resolved scales using a line-of-sight column-density method, with a comprehensive suite of fixed and adaptive attenuation laws. A decoupled kinematics model independently Doppler-shifts the stellar and nebular components, enabling realistic synthetic integral field unit data cubes. It also provides features to add observational realism, including point-spread function convolution and noise simulation. Beyond generating imaging and spectroscopic data cubes, GalSyn reconstructs spatially resolved physical property maps and star formation histories (SFHs) of a galaxy. Alongside this paper, we present the first data release of synthetic imaging observations and resolved SFHs generated from the IllustrisTNG simulations. This release includes four mock extragalactic survey fields (spanning 5, 8, 137, and 365 arcmin ² ) together with data cubes of the individual galaxies within them, data cubes of 290 local massive galaxies and their progenitors tracked across 0 < z < 5, and 259 major-merger systems. Each galaxy data cube contains imaging across 47 filters spanning the Hubble Space Telescope (HST), JWST, Euclid, Rubin/LSST, and the Roman Space Telescope.

The James Webb Space Telescope (JWST) has extended the frontier of galaxy detection to redshifts z > 11, finding a high abundance of UV-bright sources that challenge theoretical models. However, most current results come from just a few fields, introducing uncertainties due to cosmic variance. Here, we constrain z ∼ 7–14 UV luminosity functions (LFs) over ∼400 arcmin ² across 36 independent sight lines from Data Release 2 of BEACON, a JWST pure-parallel NIRCam multiband imaging survey. We identify 164 7 < z < 12 galaxy candidates: 150 F090W, 14 F115W, and no robust F150W dropouts. In the 11 pointings overlapping with public JWST spectroscopy, we find no contaminants, indicating a high purity in our sample. Our z ∼ 7.5 UV LF agrees with previous bright-end measurements but yields lower number densities at −21 ≤ M _UV ≤ −19. At z ∼ 10, our measurements are lower than most photometric JWST results but match spectroscopic constraints, consistent with the high purity of our selection. The LFs at z ∼ 7.5 and 10 are consistent with pre-JWST models, while our limits at z > 13 do not rule out a possible excess. We measure significant clustering of bright ( M _UV < −20.5) galaxies at 7 < z < 10. Fields hosting such sources are approximately 3 times more likely to be overdense relative to the full survey, implying that UV-bright galaxies preferentially reside in the most massive halos at these redshifts. Comparing with seminumerical simulations, we estimate that M _UV < −20.5 galaxies inhabit halos ∼0.8 dex less massive at z ∼ 11 than at z ∼ 8, consistent with a shift to higher star formation rates. However, their observed clustering exceeds predictions from pre-JWST luminosity–halo mass relations, suggesting these sources reside in more massive halos than previously modelled and/or multiple halo occupation.

We systematically search for galaxy overdensities using 20 independent fields with a minimum of six filters (F090W, F115W, F150W, F277W, F356W, and F444W) from BEACON, the JWST Cycle 2 NIRCam pure-parallel imaging survey. We apply an adaptive kernel-density estimation method that incorporates the full photometric redshift probability distribution function of each galaxy to map galaxy overdensities, and identify 207 significant (>4 σ ) overdensities at 1.5 < z < 5. We measure the quenched galaxy fraction, the average specific star formation rate (sSFR), the total dark matter mass, and the local galaxy density of each system. By investigating the correlation among these observables, we find that galaxy quenching proceeds in two paths. (i) Overdensities within more massive halos exhibit higher quenched fractions and lower averaged sSFRs. This trend weakens at z ≳ 2, consistent with cold gas streams penetrating shock-heated massive halos and sustaining star formation activity at early times. (ii) We also find a dependence of the same parameters on local densities at z < 2, where the quenched fraction increases and the sSFR decreases toward higher densities. The environmental trend in sSFR weakens at z ∼ 2–3 and shows tentative evidence for a reversal at z > 3, potentially due to a larger cold gas supply in earlier times. Our study reveals a complex interplay between individual galaxies and large-scale environmental properties, marking the onset of environmental effects on galaxy quenching in massive halos at cosmic noon.

We present a parametric strong-lensing model for the galaxy cluster MACS J1931.8-2635 ( z _l = 0.35), accompanying the detection of the spectroscopically confirmed SN Eos at z = 5.13. We identify 10 new multiple-image systems in recent VENUS JWST/NIRCam imaging, so that the model is constrained with a total of 19 robust multiple-image systems—nine of which also have a spectroscopic redshift. For the point-like source corresponding to SN Eos, our model predicts a total of five images, with the observed radial image pair having a similar magnification of μ ≃ 25–30 and a small time delay of . ″ 44. We present the lens-modeling results, including newly identified systems such as a triply imaged, grand-design spiral galaxy candidate at z ≃ 3.6 5 − 0.09 + 0.04 , and discuss the potential of using high-redshift lensed SNe for cosmography.

We present a catalog of 57 high-redshift z > 6 galaxy candidates, including 14 spectroscopic confirmations ( z = 6.10–9.25), 2 little red dots ( z = 4.77, 5.81), and 2 interlopers ( z = 3.23, 3.72), based on JWST NIRCam imaging (seven filters), NIRSpec spectroscopy (PRISM and G395H), and archival HST imaging (17 filters) of the strong lensing galaxy cluster MACS0647. Our highest redshift confirmation ( z = 9.25) is an extremely blue galaxy, and here we identify a spectral turnover likely due to damped Ly α . We identify an overdensity of galaxies with spectroscopic redshifts z = 6.1, confirming the z ∼ 6 overdensity identified in HST images. In one of these galaxies, our high-resolution G395H spectroscopy reveals two spatially resolved components with a velocity difference of ∼90 km s ⁻¹ ; if these components are gravitationally bound, this would imply a dynamical mass on the order of ∼10 ⁸ M _⊙ given their projected separation. We present spectral line fluxes, widths, and derived physical properties, including stellar masses (10 ⁸ –10 ⁹ M _⊙ ) and metallicities (10%–40% Z _⊙ ) for our spectroscopic sample. We note half of our NIRSpec data was obtained with standard three-slitlet nods and half was obtained with single slitlets yielding similar results, demonstrating the power to observe more sources on a densely packed NIRSpec microshutter assembly.

We report the discovery of a doubly imaged little red dot (LRD) candidate behind the galaxy cluster Abell 383, which we dub A383-LRD1. Initially classified as a dropout galaxy in HST imaging with several ground-based emission line detections placing it at z _spec = 6.027, new JWST/NIRCam observations taken as part of the cycle 4 VENUS survey now reveal that the source consists of two underlying components. These consist of a red point-source with a V-shaped SED consistent with LRD selection criteria and a nearby (∼380 pc) compact blue companion, which was the main contributor to the previous rest-frame UV detections. Based on lensing symmetry and its SED, the LRD appears to lie at a similar redshift as well. The magnification of the two images of A383-LRD1 is μ _A = 16.2 ± 1.2 and μ _B = 9.0 ± 0.6, respectively, and the predicted time delay between them is Δ t _grav = 5.20 ± 0.14 yr (∼0.7 yr in the rest-frame). After correcting for the lensing magnification, we derived an absolute magnitude of M _UV, LRD = −16.8 ± 0.3 for the LRD and M _UV, BC = −18.2 ± 0.2 for the blue companion. We performed SED fits to both components, revealing the LRD to show the best fit with a black hole star (BH*) model and a substantial host galaxy, along with the blue companion with an extremely young, emission-line dominated star-forming nebula. If it is verified spectroscopically in the future, A383-LRD1 would represent the second known multiply imaged LRD detected to date, following A2744-QSO1. To our knowledge, it would also stand as the first LRD system with a confirmed detection of [C II ] λ 158 μm emission from ALMA observations. Thanks to the lensing magnification, this system opens a unique door to studying the relation between a LRD, its host galaxy, and its environment. It represents a prime candidate for deep JWST spectroscopy and high-resolution ALMA follow-up observations.