arXiv subjects

Rogier A. Windhorst

Publications and source records attributed to Rogier A. Windhorst.

At least 19 recordsLinked to original sources

arXiv2026

PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time-Domain Field IV: X-Ray Variability Analysis

NuSTAR and XMM-Newton have observed the James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF) for almost five contiguous years starting in 2019. In that time, the NEP X-ray survey has accumulated 3.5 Ms and 228 ks of quasi-simultaneous NuSTAR and XMM-Newton observations, respectively. This paper presents variability results for the 112 NuSTAR and 453 XMM-Newton sources detected in this field, based solely on the X-ray photometric data. Four NuSTAR sources and 11 XMM-Newton sources varied in at least one band at >=99% confidence. The sources with redshift measurements show a relationship between luminosity and variability with 74% of variable sources brighter than 5x the sensitivity limit of the survey. This is supported by about 1/3 of sources with more than 400 counts detected being variable and only 4 sources with fewer counts showing variability. Variability timescales are not well determined, but variability amplitude tends to be larger on longer timescales.

astro-ph.HE↗

arXiv2026

Spatially Resolved Physical Properties of Young Star Clusters and Star-forming Clumps in the Brightest z>6 Galaxy, the Strongly Lensed Cosmic Spear at z=6.2

We present 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 $z_{\rm spec}=6.2$. New JWST NIRCam imaging and high-resolution NIRSpec 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 $R_{\rm{eff}} \lesssim 8$ pc, stellar masses of $M_{*} \sim 10^{6}-10^{7}\,M_{\odot}$, and high stellar mass surface densities of $Σ_{*} \gtrsim 2\times 10^{4}\,M_{\odot}~\rm{pc}^{-2}$. While their stellar populations are very young ($\sim 6-11$ Myr), their dynamical ages exceed unity, consistent with the clusters being gravitationally bound systems. Placing the star clusters in the size vs.~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 ($ξ_{\rm{ion}}$) is slightly suppressed in this central region, potentially indicating a locally elevated Lyman continuum escape fraction facilitated by feedback-driven channels.

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arXiv2026

Constraints on the Pop III Sky Surface Brightness from High-Redshift Caustic Transients in MACS0416

Population III (Pop III) stars are hypothetical zero-metallicity stellar structures formed from primordial hydrogen and helium. They are theorized to span a wide mass range, extending to several 100 solar masses, and may have played important roles in nucleosynthesis and reionization. Their expected fluxes are far below JWST NIRCam detection limits, making direct observation unlikely. However, extreme magnification near the caustics of massive foreground galaxy clusters may enable their detection. We search for overlooked high-redshift (7 <= z <= 17) caustic transits in the lensing cluster MACS J0416.1-2403. Using three observations spanning 126 days, we create difference images to identify potential candidates. Critical curves for sources at 7 <= z <= 17, derived from a strong-lensing model, guided visual inspection of three difference-images. No additional transits were found. The longer caustics in our model sweep a larger source-plane area, increasing the probability of detecting an event. Combining this increased statistical sensitivity with deeper imaging, we establish a fainter limit for the unresolved stellar population at z >= 7. From this null result, we constrain the 100 solar mass 2 micron Pop III sky surface brightness to >= 32.8 +/- 0.6 mag arcsec^-2. Modeling the non-detection as a Poisson process gives a posterior mean caustic-transit rate of 0.29 cluster^-1 yr^-1 and a 95 percent upper credible limit of lambda_95 = 0.86 cluster^-1 yr^-1. The inferred rate remains consistent with the adopted fiducial Pop III caustic-transit model and provides an empirical benchmark for future multi-epoch monitoring campaigns. This search exploits the fact that individual stars projected close to source-plane caustics can be briefly magnified far beyond their unlensed fluxes. These constraints provide a direct test of the abundance of luminous Pop III stars at early cosmic times.

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arXiv2026

The Roman eXtreme Deep Field (RXDF)

The Roman eXtreme Deep Field (RXDF) program is one of the five General Astrophysics Survey (GAS) programs approved for observing time with the Nancy Grace Roman Space Telescope in Cycles 1 and 2. It has been allocated 386.41 hours to carry out an imaging survey to AB = 30 mag (5-sigma) over ~140x larger area than the Hubble eXtreme Deep Field (HXDF) full-depth area (ACS+WFC3/IR). The RXDF will cover the full Roman wavelength range with 7 bands, reaching AB = 30 mag in RZYJH, 29 mag in F, and 28 mag in K, over a full-depth area of 678.75 arcmin^2 embedded in a total area of 1,243 arcmin^2, and far exceeding the depths of the Roman Core Community Surveys (CCS). The RXDF is within the Euclid Ultra Deep Field (EUDF) near the North Ecliptic Pole (NEP), a strategic long-term field for generational space facilities, with a wealth of multi-wavelength data including extensive coverage from the James Webb Space Telescope (JWST) NEXUS Treasury program. The observations will cover 3 epochs at a 1-year cadence, each epoch divided into 3 sub-epochs ~10 days apart, enabling time-domain studies on time baselines from ~10 days to over ~2 years. The RXDF is uniquely positioned to address critical questions in reionization, large scale structure (LSS), growth of supermassive black holes (SMBHs), little red dots (LRDs), and high-z supernovae (SNe); the volumes probed by HST+JWST are too small at these extreme depths, and even the deepest CCS tiers are too shallow. In addition to our key objectives, a wealth of additional science will be enabled by engaging the community with our rapidly released datasets, revolutionizing a wide range of science for a lasting legacy. This short document, which is converted from the approved RXDF proposal, aims to provide the community with a summary of the program.

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arXiv2026

The Koi Pond: A Strongly Lensed Protocluster Core hosting a Diverse Population of DSFGs

We present James Webb Space Telescope (JWST) and Atacama Large Millimeter Array (ALMA) observations of PJ0846+15, \textit{The Koi Pond}, a strongly lensed protocluster core at Cosmic Noon. This field offers a magnified view of 11 dusty star-forming galaxies (DSFGs) all at $z=2.67$ (within $ΔV=800$ km s$^{-1}$) spanning a projected extent of $>300$ kpc lensed by a $z=0.77$ foreground cluster. NIRCam and ALMA Band 6 continuum measurements map the stellar distribution and thermal dust emission respectively at a spatial resolution of $\sim$0.15$^{\prime\prime}$. This analysis reveals a diverse population of DSFGs, with evidence of both interacting and non-interacting systems exhibiting a wide range of morphological features including spiral arms, bars, bulges, clumps/stellar clusters, tidal tails/debris and displaced molecular gas reservoirs. Comparing the rest-frame J- band continuum (F444W) vs (i-J) color (F277W$-$F444W), we find a wide range of values, suggesting a $>$1-dex spread in stellar mass and a dust attenuation reddening of $ΔA_{\mathrm{V}} > 1$ mag. The DSFG members exhibit varying dust sizes relative to the stellar emission, ranging from compact dusty cores to galaxy-wide emission. Resolved color maps of individual sources showing a spread as high as F277W$-$F444W$=2$ mag suggesting complex stellar-to-dust geometry. Although gas-rich mergers are identified in the core, the most red and dust emitting members are disks exhibiting clumpy structure indicating secular growth can drive these starburst events. Such a remarkable range in properties within this sample suggest DSFGs in protocluster core environments follow diverse evolutionary pathways towards their transition into quiescent, elliptical cluster galaxies.

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arXiv2026

PASSAGES: The Discovery of a Strongly Lensed Protocluster Core Candidate at Cosmic Noon

Investigating the processes by which galaxies rapidly build up their stellar mass during the peak of their star formation ($z=2-3$) is crucial to advancing our understanding of the assembly of large-scale structures. We report the discovery of one of the most gas- and dust-rich protocluster core candidates, PJ0846+15 (J0846), from the Planck All-Sky Survey to Analyze Gravitationally lensed Extreme Starbursts (PASSAGES) sample. The exceedingly high total star formation rate (SFR) uncorrected for lensing magnification ($μ$) of $μ\text{SFR} = 39900^{+23000}_{-12900} \text{ M}_\odot\text{ yr}^{-1}$ is the result of a foreground cluster lensing at least 11 dusty star-forming galaxies between $z=2.660-2.669$, where the intrinsic value is estimated to be $\text{SFR} = 5200^{+3200}_{-2000} \text{ M}_\odot\text{ yr}^{-1}$. Atacama Large Millimeter Array (ALMA) observations uncovered 18 CO(3--2) emission-line detections, some of which are multiply-imaged systems, lensed by a foreground cluster at $z=0.77$. We present the first multi-wavelength characterization of this field, constructing a lens model that predicts that these 11 galaxies ($μ\simeq 1.5-25$) are contained within a projected physical extent of $280 \times 150 \text{ kpc}$, with a velocity dispersion of $σ_{v} = 246 \pm 72 \text{ km s}^{-1}$. J0846 exhibits the rare case of a protocluster candidate whose core is strongly-lensed, offering a magnified view of the rapid stellar buildup within an overdense environment at Cosmic Noon.

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arXiv2026

VENUS: A Strongly Lensed Clumpy Galaxy at $z\sim11-12$ behind the Galaxy Cluster MACS J0257.1-2325

We present the discovery of a strongly lensed galaxy at $z\sim11-12$, dubbed the ``Misty Moons'', identified in the JWST Treasury Survey, Vast Exploration for Nascent, Unexplored Sources (VENUS). 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 lensing models. Two of the five images, ID1 and ID2 ($μ\sim 20-30$), are very bright (F200W$\sim26$ AB mag) and exhibit blue SEDs with prominent Ly$α$ breaks. In the source plane, the Misty Moons is a sub-$L^*$ galaxy ($M_{\rm UV}\sim-18.0$ mag) resolved into multiple stellar clumps, each of which has an effective radius of $r_\mathrm{eff}\sim 10-70$ pc and a stellar mass of $\sim10^7\ M_\odot$. These clumps dominate the stellar mass budget of the Misty Moons ($\gtrsim80\%$), 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 $z\gtrsim10$ faint galaxies, such as JADES-GS-z13-0 and JADES-GS-z14-1, indicating that the Misty Moons represents a typical $z\gtrsim10$ 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 $z\gtrsim10$.

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arXiv2026

Two Exciting High-redshift Galaxy Candidates Turn Out to Be Two Exciting Ultra-cool Brown Dwarfs

From the onset of observations of JWST we have discovered unexpectedly luminous galaxies at redshifts $z>10$ and as high as $z=14$. With their discovery, the question immediately followed as to where their progenitors are, since such progenitors should be within reach of existing surveys. However, the discovery of several bright candidates at $z>15$ may indicate further discrepancies between pre-JWST model predictions and current observations. Progenitors of the bright $z\sim 14$ galaxies should be visible at redshifts as high as $z\sim 20-30$, showing in the data as F277W and F356W dropouts. We identify two such candidates in the Bullet Cluster JWST data; however, subsequent NIRSpec follow-up data show spectra that can be well fit with Y dwarf templates with temperatures ${272\mbox{--}351\mbox{K}}$ and ${445\mbox{--}525\mbox{K}}$ (using ATMO2020 and Sonora Elf Owl models) and distances of $\sim 150\mbox{--}650\mbox{pc}$. The first is one of the lowest-temperature brown dwarfs known, and the lowest-temperature brown dwarf detected spectroscopically outside the solar neighborhood. With additional NIRCam imaging taken $\sim 1$ year later, we also detect their proper motions of $(49 \pm 8)\,\mbox{mas/yr}$ and $(24 \pm 3)\,\mbox{mas/yr}$, further indicating that at least some F277W and F356W dropouts are sub-stellar cold Milky Way objects such as brown dwarfs.

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arXiv2026

PEARLS: JWST Counterparts of Micro-Jy Radio Sources in the NEP Time Domain Field. II. All Four Spokes

JWST/NIRCam observations in the North Ecliptic Pole Time Domain Field (TDF) identify 4.4 micron counterparts for 206 of 211 radio sources with S(3 GHz) \gapprox 5 micro-Jy in a 65arcmin^2 field. One of the remaining radio sources is likely to be a radio lobe of a nearby Seyfert galaxy, and the four radio sources without counterparts could be spurious. All but five counterparts are brighter than magnitude 23.5 AB at 4.4 micron. A simple position match with radius 0.3 arcsec would have identified 198 of the counterparts but only in a 4.4 micron catalog created with aggressive deblending of multiple peaks within an object's brightness distribution into distinct catalog sources. The properties of the radio-host galaxies are mostly consistent with those found in Paper 1: the median redshift is 1.14, and the radio emission, calculated taking into account the non-linear dependence of radio luminosity on star-formation rate, is consistent with a star formation origin in ~79% of the sample. For the other ~21%, the radio flux could come from star formation hidden behind dust or from an active galactic nucleus. One difference from other studies of radio-source counterparts is that 66% of the radio hosts show at least one indication of an AGN's presence. The presence of AGN and of hidden star formation could be elucidated by monitoring for source variability, and the TDF is the field most suited to such observations.

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arXiv2026

Spectral Energy Distributions of Globular Clusters in VV191a

We investigate globular cluster (GC) candidates associated with the elliptical galaxy VV191a using JWST NIRCam and archival HST imaging. Beginning with an initial catalog of over 500 candidate sources, we apply morphological filtering, photometric redshift selection, and spectral energy distribution (SED) fitting using BAGPIPES to isolate a refined sample of 61 probable GCs, including a high-confidence subset of 20 objects. The derived age distribution is concentrated between ~ 6-10 Gyr, with a peak near ~ 8 Gyr, while metallicities are predominantly near and super-solar. Unlike many GC systems in elliptical galaxies, the VV191a sample does not exhibit a clear bimodal metallicity distribution. Derived stellar masses span a broad range and suggest significant degeneracies related to dust attenuation and foreground contamination from the overlapping spiral galaxy VV191b. These results support the presence of an evolved GC population in VV191a while highlighting limitations imposed by broadband SED fitting and foreground contamination

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arXiv2026

VENUS: an ultra-faint galaxy hosting the metal-poor type II supernova at $z=5.13$ Witnessing the initial metal enrichment with extremely frequent core-collapse supernovae?

We present the first characterization of the host galaxy of a recently discovered type IIP SN at $z=5.13$ (SN Eos). SN Eos and its host galaxy are gravitationally lensed and multiply imaged. The total magnification $μ\sim53$ enables spatially resolving the system, allowing us to localize the core-collapse supernova (CCSN) position and to characterize its local environment within an early galaxy. Our observation reveals that the host is an ultra-faint ($M_{\rm UV}=-14.4\pm0.3$ mag) Lyman-$α$ emitter with a very high equivalent width. The host galaxy also shows very weak [O iii]4959,5007 lines despite an H$α$ line detection ([O iii]5007/H$β<0.7$ with case B recombination). Assuming that the weak [O iii] is due to low gas-phase metallicity given the low-metallicity of SN Eos itself, SN Eos plausibly marks the formation and explosion of a metal-poor star in an extremely metal-poor environment ($<1\ \%\ Z_\odot$), facilitating the initial stages of the chemical enrichment of the host. Finding the CCSN in such an ultra-faint galaxy at $z=5.13$ also indicates that the SN rate could be considerably higher in high-$z$, metal-poor environments, potentially implying e.g., a $Z$-dependent IMF, $Z$-dependent massive star explodability, or runaway stellar collisions in dense star clusters. Without lensing, only SN Eos would be detectable and the host would be below the detection limit in any NIRCam surveys ever performed. The Eos host galaxy can thus be representative of the origin of {\it hostless} supernovae frequently found in JWST blank field surveys.

astro-ph.GA↗

arXiv2026

VENUS: Strong-lensing model of MACS J1931.8-2635 -- revealing the farthest multiply imaged supernova

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 $z = 5.13$ (Coulter et al. 2026). 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 $μ\simeq 25 - 30$ and a small time delay of $< 5$ days, in agreement with their simultaneous observation. According to the model, the other three predicted images arrived earlier, with time delays of $3.6 \pm 0.7$, $3.4 \pm 0.7$ and $53.9 \pm 10.8$ years prior to the two observed images, and with magnifications of $14.5 \pm 2.9$, $11.9 \pm 2.4$ and $2.2 \pm 0.4$, respectively. The absence of detections at the predicted positions, where the host galaxy's images are also visible, confirms the transient nature of the source. SN Eos and its host galaxy are studied in separate articles, and we here focus on the lens model. The final model reaches a very good $r.m.s.$ distance between model and observations of $0.44''$. We present the lens-modeling results, including newly identified systems such as a triply imaged, grand-design spiral galaxy candidate at $z \simeq 3.65_{-0.09}^{+0.04}$, and discuss the potential of using high-redshift lensed SNe for cosmography.

astro-ph.CO↗

arXiv2026

A massive barred spiral galaxy at z = 5.102 discovered by JWST

We report M1149-BSG-z5, a barred spiral galaxy at $z = 5.102$, identified in the parallel field of MACS J1149+2223 with JWST and HST. M1149-BSG-z5 is the highest redshift barred galaxy candidate to date. Both isophote ellipse fitting and structural modeling support a stellar bar of length $a_\mathrm{bar} \approx 4.5$ kpc, and extended spiral arms peaking at $r \approx 5.5$ kpc. M1149-BSG-z5 is a massive main sequence star-forming galaxy, with a stellar mass of $10^{10.45}\rm M_\odot$ and a star-formation rate of $144\,\rm M_\odot/yr$. A concentrated bulge is embedded in an extended disk with a global Sérsic index $n = 2.37$. With an effective radius of $R_{e} = 2.61\rm \ kpc$, M1149-BSG-z5 is larger than typical galaxies at $z \sim 5$ and comparable to barred galaxies at $2 < z < 4$. M1149-BSG-z5 also hosts a broad-line AGN, with a relatively low black-hole-to-stellar mass ratio of $\rm M_{\rm BH}/M_\ast\sim10^{-3}$. Its metal-enriched emission-line properties indicate that it is already chemically evolved. These properties imply M1149-BSG-z5 as an early-assembled and structurally evolved galaxy. We also find that M1149-BSG-z5 resides in an overdense region with a nearby companion galaxy, suggesting an interaction-driven bar formation mechanism. Its concentrated light, early assembly and main-sequence star formation also suggest baryon-dominated, gas-rich conditions, where gravitational instability can further accelerate the bar formation.

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arXiv2026

PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time Domain Field VI: Multiwavelength SED Analysis

We model spectral energy distributions of 261 X-ray sources to $z \sim 5$ in the North Ecliptic Pole Time Domain Field, extending prior XMM-Newton and NuSTAR analyses. Using the star-forming main sequence (SFMS) and black hole accretion rate (BHAR) frameworks, we find that SFRs generally lie below the SFMS while most BHARs exceed the population average, as expected for X-ray-selected samples. There is a strong correlation ($ρ=+0.73$) between SFR relative to the SFMS and specific AGN luminosity, $L_{AGN}/M_*$; galaxies with the highest $L_{AGN}/M_*$ exist at or above the SFMS. X-ray luminosity correlates with SFR ($ρ=+0.80$), revealing a star-forming and X-ray luminous "cold quasar" population consistent with dramatic, short-timescale accretion episodes. Low-mass galaxies show BHARs well above the population averaged value for their mass whereas high-mass galaxies' SMBHs accrete at the population averaged BHAR, suggesting "growth spurt" and "maintenance-mode" accretion, respectively. Traditional AGN classifications (obscured, unobscured, or radio-loud) do not reveal these distinctions, demonstrating the X-ray perspective's unique ability to identify rare AGN phases that are critical for the instantaneous link between galaxies and their SMBHs.

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arXiv2026

We Must Preserve Hubble given its Unique Complementarity to Webb, Roman, and Euclid

We present compelling arguments -- focusing on galaxy science -- for preserving the main imagers and operational modes of the Hubble Space Telescope (HST) for as long as is technically feasible, to assure maximum complementarity to the James Webb Space Telescope (JWST), Roman, and Euclid. HST was designed to work well over the 0.1-1.6 $μ$m wavelength range, and its unique UV-optical performance has fundamentally contributed to our understanding of galaxy assembly and the Cosmic Star Formation History (CSFH). While star-formation started at redshifts $z \gtrsim 10$, when the universe was less than 500 Myr old, the CSFH did not peak until $z \simeq 1.9$ (i.e., about 10 Gyr ago), and has steadily declined since that time. Hence, at least half of all stars in the universe formed it in the last 10 Gyrs where HST provides its unique rest-frame UV view of unobscured young, massive stars tracing cosmic star-formation, as well as unobscured Active Galactic Nuclei (AGN). HST thus uniquely probes (unobscured) young, hot, massive stars and AGN in galaxies, while JWST, Euclid and Roman reveal more advanced stages of older stellar populations, as well as relatively short-lived phases where galaxies produce and shed a lot of dust from intense star-formation, dusty AGN, and the very high redshift universe ($z \gtrsim 10$) not accessible by HST. HST is thus highly complementary to these other facilities, all of which took decades to build to ensure decades of operation. To maximize return on investment in these facilities, ways will need to be found to operate HST imaging instruments in all relevant modes for as long as possible into the JWST and Roman missions.

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arXiv2026

Testing Lens Models of PLCK G165.7+67.0 Using Lensed SN H0pe

Supernova H0pe is a multiply-imaged Type Ia supernova (SN~Ia) and the second lensed SN to yield a measurement of the Hubble constant by the time-delay cosmography method, finding $H_0 = 75.4^{+8.1}_{-5.5} \text{km s}^{-1} \text{Mpc}^{-1}$ (Pascale et. al 2025). We investigate the seven lens modeling approaches used to derive $H_0$, assessing their agreement with $Λ\text{CDM}$ constraints from SN~Ia surveys through a purely observational comparison. \textbf{We test each lens model by combining its predicted magnifications with the observed time delays to reconstruct the intrinsic SN~Ia luminosity and corresponding distance modulus.} While photometrically derived magnifications yield distance moduli in line with $Λ\text{CDM}$ expectations, our comparison reveals that lens model predictions, even the most precise ones, \textbf{consistently overestimate the magnification, with an offset $> 1$~mag}. This known bias, already appreciated by modeling teams, is independently confirmed through our analysis and highlights the value of lensed SNe as a tool to test model accuracy. If unaccounted for, such magnification biases can propagate into uncertainties in derived cosmological parameters, including $H_0$, a critical challenge for precision cosmology using strongly lensed transients.

astro-ph.CO↗

arXiv2026

First Statistical Study of Over 100 Magnified Stellar Events at Redshift $z \approx 0.725$ with JWST

Highly magnified stars at cosmological distances ($z \gtrsim 0.7$) become detectable thanks to microlensing by intracluster stars near the critical curves of galaxy clusters. Multi-epoch photometric campaigns targeting caustic crossing galaxies magnified by massive galaxy clusters enable the detection of these objects as transient events. Such stars provide unique opportunities to study stellar populations at early cosmic times, probe the nature of dark matter, reveal small-scale structure in the cluster, and improve lens models. To date, only a few dozen high-redshift stars have been reported, with a single lensed galaxy, the Dragon, holding the current record of 44 detections. These numbers, however, remain insufficient to exploit their full potential. In this paper, owing to the inclusion of new observations, we report the identification of more than 100 magnified stellar events in the Dragon, behind the massive galaxy cluster Abell 370. The relatively low redshift of the Dragon ($z\approx0.725$) facilitates the detection of its most massive stars. Using imaging data from three different cycles (2022--2024) with the James Webb Space Telescope, we apply a time-domain technique to identify flux variations associated with caustic-crossing events. From the spatial distribution of stellar events we constrain the high-end slope of the stellar luminosity function, finding $β=2.18^{+0.20}_{-0.30}$. Alternatively, assuming a fixed slope, we constrain the microlens surface mass density. In addition, we examine the parity asymmetry of the detected caustic-crossing events, a proposed probe of wave dark matter, and find that it remains present. We also use the events to trace the regions of highest magnification, offering an alternative way to map the system critical curves.

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arXiv2026

PEARLS: Two Distinct Populations of AGN Hosts Moving Between Star Formation and Quiescence

We present the results of AGN--host-galaxy decomposition using JWST/NIRCam, HST/ACS, and HST/WFC3 imaging of the North Ecliptic Pole Time Domain Field (NEP-TDF). The light-profiles of 36 NIRCam-selected AGN candidates are modeled for measurement of their point sources, and point source-subtracted host-galaxy emission is used in SED modeling for star formation rate (SFR) estimation. Offsets from the canonical star-forming main sequence (SFMS) show that the host galaxies form two distinct groups distinguished by their star formation: a ``bridge'' between the moderate SFRs of radio sources and low SFRs of X-ray sources, and a cleanly-separated ``branch'' above $Δ\rm SFMS = -1$ whose SFR trends positively with AGN fraction. Branch galaxies include late-type galaxies with X-ray and radio detections and more dominant point sources that are most certainly AGN, while bridge galaxies have predominantly early-type morphologies with weaker point sources that may be due to compact stellar bulges. Both groups show evidence of recent transition between star formation and quiescence, but neither group shows preference for higher or lower stellar mass or redshift, suggesting that star formation in NIRCam-selected AGN-hosts is more strongly determined by AGN activity than by stellar mass.

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