arXiv subjects

Jacqueline Antwi-Danso

Publications and source records attributed to Jacqueline Antwi-Danso.

At least 19 recordsLinked to original sources

arXiv2026

Why a Multi-Cycle Treasury Program is Essential to Maximize JWST's Scientific Contributions to Galaxy Formation

The Genesis Initiative is an extragalactic community-wide effort to coordinate white papers in response to the STScI Multi-Cycle Treasury (MCT) concept call. Two of JWST's primary science goals are to discover and characterize the first stars and galaxies, and to understand how they evolved into the galaxies we see today - questions whose fundamental importance has been affirmed by the past three decadal surveys. JWST's first five years have surpassed expectations, revealing a bounty of unexpected discoveries about the early universe. Yet these discoveries have raised as many questions as they have answered, and key mission goals remain unmet. Transforming this excitement into a quantitative physical understanding of early galaxy formation requires a uniform, statistically controlled legacy dataset that the current portfolio of smaller, heterogeneous programs cannot provide. The history of the Hubble Space Telescope offers a clear precedent. Its most transformative extragalactic results came from large, coordinated surveys far exceeding what the standard time-allocation process typically approves, and these uniform datasets remain scientifically productive decades later. We argue that JWST is now poised for the same leap. Answering the field's central open questions demands coordinated, community-led surveys of ~1000-2000 hr, with uniform and well-characterized selection functions that are structurally impossible within single-cycle programs. Such an investment is time-critical while JWST's instruments remain at peak performance, and would maximize synergy with ALMA, Euclid, Roman, Rubin, and future facilities. We therefore urge STScI to open a MCT channel, enabling the bold, ambitious surveys needed to understand how galaxies evolve from first light to the present day.

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arXiv2026

Dust Survival in Lensed Quiescent Galaxies at $z>1$ Depends on How They Quench

The interstellar medium of massive quiescent galaxies holds key clues to how they quench, yet remain poorly understood. Although dust is expected to be depleted rapidly ($\lesssim$100 Myr) after quenching, some quiescent galaxies host substantial dust reservoirs, raising the question of whether dust survives quenching or is replenished afterward. We present ALMA Band 6 continuum observations ($λ_{\mathrm{rest}}$$>$250$μ$m) of eight strongly-lensed, spectroscopically-selected quiescent galaxies at z$\sim$1-2.5 from the COOL-LAMPS and REQUIEM surveys, plus five archival REQUIEM systems. The sample spans more than two orders of magnitude in dust-to-stellar-mass ratio ($f_{\mathrm{dust}}<10^{-5}$ to $>10^{-3}$), and two galaxies host extended, resolved dust. Comparing $f_{\mathrm{dust}}$ with time since quenching, roughly half the sample, preferentially at higher redshift, is consistent with rapid quenching and harsh dust destruction, while lower-redshift, more slowly quenched systems are consistent with milder destruction, possibly reflecting an evolving dominant quenching mode. The two most dust-rich galaxies exceed even the mildest model destruction tracks, with J1201-3952 retaining the highest $f_{\mathrm{dust}}$ $\sim$1.8 Gyr after quenching. If these systems are truly quiescent, their dust masses approach maximum stellar yields, pointing to ISM grain regrowth and/or TP-AGB dust production. However due to our single-band continuum data, $f_{\mathrm{dust}}$ is uncertain ($\pm$0.3 dex systematic uncertainty from the unknown dust temperature) and we cannot rule out obscured star formation in these two galaxies. Our results suggest that dust survival depends on how galaxies quench: rapid, harsh quenching efficiently destroys dust, while slower, milder quenching can leave dust reservoirs that persist or are replenished long after star formation ceases.

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arXiv2026

A Supermagnified Little Red Dot with a Resolved Host

Little red dots (LRDs) are an intriguing new class of sources in the early universe discovered by the James Webb Space Telescope (JWST) characterized by V-shaped spectra and extremely compact sizes. Their underlying mechanisms still remain the subject of ongoing debate. We present JWST observations of a gravitationally lensed LRD nicknamed "Best Friend" at $z_{\rm spec} = 8.297\pm0.002$. Its high magnification factor of $μ= 36^{+8}_{-12}$ makes it the highest magnified LRD reported to date and unveils both the resolved structure of its host and a central engine less than 7 pc in size. The spectrum of the central engine, in which broad lines are not detected, possibly owing to the limited S/N and spectral resolution, is better interpreted as black hole activity rather than a dense star cluster. The latter cannot be fully excluded, but if true, the resulting lower limit on stellar density would be $>1.25^{+0.4}_{-0.3}\cdot10^6 \mathrm{M_{\odot}/pc}^2$, which is around 2 orders of magnitude higher than stellar densities of typical clusters at high-z. By performing a spatially resolved analysis of NIRCam photometry and NIRSpec/PRISM spectroscopy, we find that the host stellar mass is $\log(M_\star/M_{\odot}) = 7.3^{+0.2}_{-0.8}$. Best Friend demonstrates the power of lensing to reveal the morphologies of LRDs.

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arXiv2026

A sub-100 pc view at z~5 of a multiply imaged massive quiescent galaxy

James Webb Space Telescope surveys reveal many rapidly assembled galaxies in the first billion years. Simulations struggle to reproduce their rapid star formation and abrupt cessation, known as quenching. Testing these models is difficult because high-redshift galaxies are compact and appear unresolved. We present VENUS-CLJ0152-QG1, a massive post-starburst galaxy at redshift 5.18. A foreground cluster lenses it into three images, yielding a physical resolution of about 70 parsecs, enough to probe quenching processes on sub-kiloparsec scales. We find a half-light radius twice as large as expected, a central stellar mass density three times lower than field analogs, and off-center ionized gas emission. These features suggest it quenched without compaction or an obvious active galactic nucleus, a departure from unlensed high-redshift galaxies that lensing makes visible.

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arXiv2026

SPAM: Survey Overview and JWST/NIRCam Multi-Band Photometry Catalog

We present the Star-formation from Photometry through the Addition of Medium-bands (SPAM) survey, a 62.9 hr JWST/NIRCam imaging program to add ten new filters, nine medium-band filters, and one broad-band filter to the CEERS legacy dataset. We describe the observation strategy, present the data, and detail the data-reduction process. We include a complete reduction of imaging in the legacy CEERS footprint, inclusive of all publicly available photometric parallel and GO observations within the legacy CEERS footprint. We present a multi-band photometric and photometric redshift catalog which includes all medium- and broad-band filters available on NIRCam. We find that adding medium bands from the SPAM and MINERVA programs improves photometric redshifts. We discuss how these data advance the SPAM survey's key science goals: better-constrained photometric redshifts, identification of high-redshift overdensity members, improved recovery of emission-line strengths, and more accurate star formation histories.

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arXiv2026

$El\ Ascua$: An ultra-luminous, radio-loud, Compton-thick AGN at $z\sim 3.8$ hiding in plain sight revealed by MINERVA multi-band MIRI observations

Heavily dust-obscured active galactic nuclei (AGN) are crucial for understanding supermassive black hole growth. Using multi-band MIRI photometry from the MINERVA survey, we report the discovery in the UDS field of an extremely mid-infrared bright Compton-thick AGN (CT AGN) at $z \sim 3.8$, \textit{el Ascua} (the Ember). The AGN and/or its host galaxy is detected at 870\,$μ$m with ALMA and at 1.4\,GHz with the VLA. With UV-to-radio spectral energy distribution modeling, we estimate that the dusty host galaxy has a stellar mass of $\log\left( M_\star / M_\odot \right)=10.82 \pm 0.57$ and a star formation rate of ${\rm{SFR}} =157 \pm 8 \,M_\odot\,{\rm yr^{-1}}$, and we confirm the presence of a powerful dusty AGN with an intrinsic accretion luminosity of $\log\left( L_{\rm{acc}} /{\rm erg\,s^{-1}} \right)=47.12 \pm 0.58$. CT obscuration is revealed by comparing the upper limit on the X-ray luminosity over $2-10 \,{\rm{keV}}$ with the $6 \,{\rmμ{m}}$ mid-IR AGN luminosity. We additionally find evidence for a radio excess by comparing its total IR-to-radio ratio to those of typical star-forming galaxies and radio-quiet AGN, implying that \textit{el Ascua} could be a rare radio-loud CT AGN. With an extremely high ratio between black hole accretion rate and SFR, the AGN is likely nearing the peak of a deeply obscured phase of black hole growth before AGN feedback blows away the obscuring material. Our work demonstrates the power of MIRI to reveal heavily obscured AGN missing from our supermassive black hole census.

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arXiv2026

The FENIKS Survey: Stellar-Halo Mass Relationship of Central and Satellite Galaxies in UDS and COSMOS at 0.2 < z < 4.5

We present the observed Stellar-to-Halo mass relationship (SHMR) spanning 0.2 $< z <$ 4.5 enabled through galaxy clustering and abundance measurements from two large (effective area $\sim$ 1.61 deg$^{2}$) and homogeneously prepared photometric catalogs $-$ UltraVISTA ultra-deep stripes DR3 (COSMOS) and FENIKS v2 (UDS). To translate these measurements into the SHMR, we introduce a novel halo occupation distribution (HOD) fitting approach (``smooth-$z$'') whereby HOD parameters between neighboring $z$-bins are disallowed sharp changes through continuity priors. As a result, the high constraining power at $z$ $\lesssim$ 2, due to a much wider dynamical range in stellar mass ($\sim$ 3 dex), helps constrain the SHMR at $z$ $\gtrsim$ 2, where that range shrinks down to $\lesssim$ 1 dex. We find a clear \textit{downsizing} trend in halo mass scale with peak integrated star-forming efficiency (SFE), M$_{h}^{peak}$ as it consistently decreases from 10$^{12.69^{+0.08}_{-0.08}}$ M$_{\odot}$ at z $\sim$ 4 to 10$^{12.17^{+0.03}_{-0.03}}$ M$_{\odot}$ at $z$ $\sim$ 0.35, exhibiting a decline of 0.52 dex. Furthermore, we show that if we had relied on COSMOS data alone (as opposed to UDS+COSMOS), as has been done by many preceding studies, M$_{h}^{peak}$ would be systematically lower by up to $\sim$ 0.2 dex at $z$ $<$ 1.25, highlighting the importance of mitigating cosmic variance. Finally, for the first time, we show how the integrated SFE evolves with redshift as halos grow in mass along their progenitor merger trees, instead of at fixed halo masses.

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arXiv2026

A Systematic Assessment of Total Stellar Mass Measurements with Spatially Resolved Photometry and Medium Bands at 1 < z < 9: The Impact of Mass-to-Light Variations and Outshining

JWST NIRCam spatially resolved photometry enables studies of galaxies' stellar populations and stellar masses on sub-kpc scales. We use JWST (CANUCS, Technicolor, JUMPS) and HST data, covering wide- and medium-band UV-IR filters to study the stellar mass bias between spatially resolved and integrated photometry of $\sim$3000 galaxies at 1 $ 10^{\mathrm{-8.5}}$ yr$^{\mathrm{-1}}$. For these high-sSFR galaxies, the median offset reaches $Δ\log_{\mathrm{10}} (M_{\ast})$ $\sim$ -0.36 dex with the largest bias occurring in low-mass ($M_{\ast} \leq 10^{\mathrm{ 9.5}} M_{\odot}$) galaxies. These results are consistent with the outshining of older populations by recent star formation. High-sSFR galaxies also show spatial variations in their mass-to-light ratios ($M_{\ast}/L_{V}$): the stellar mass bias decreases with $σ[\log_{\mathrm{10}}(M_{\ast}/L_{V})]$ for galaxies with $10^{\mathrm{-8}} \leq \mathrm{sSFR}[\mathrm{yr}^{\mathrm{-1}}] < 10^{\mathrm{-9}}$, with the strongest trend for $10^{\mathrm{-7}} \leq \mathrm{sSFR}[\mathrm{yr}^{\mathrm{-1}}] < 10^{\mathrm{-8}}$, quantified by the Spearman correlation coefficient $ρ_{\rm S}=-0.37$. While medium bands are important for constraining stellar masses from integrated photometry, spatially resolved photometry reduces the impact of their absence, with dispersion offsets of $Δ\log_{\mathrm{10}} (M_{\ast})$ = 0.33 dex for integrated photometry but 0.15 dex for resolved photometry when only wide-bands are included.

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arXiv2026

CHAMPS: Data Reduction and Detection of ~3300 Dusty Galaxies at 1.2 mm

We present the reduction and source catalogs for the \textit{COSMOS High-$z$ ALMA-MIRI Population Survey} (CHAMPS), the largest Atacama Large (Sub)Millimeter Array (ALMA) blank field survey to date at 0.2\,deg$^2$. With observing frequency centered at $250\, $GHz ($1.2\,$mm) and bandwidth of 7.5 GHz, CHAMPS covers the JWST/NIRCam+MIRI footprint in the COSMOS field, taking advantage of the rich, multiwavelength ancillary datasets in COSMOS ranging from X-ray to radio. The majority of the CHAMPS survey (90$\%$) has depths at or below 200 $μ$Jy beam$^{-1}$ and with an average RMS of 146 $μ$Jy beam$^{-1}$. The reduced CHAMPS mosaic has a beam size of $θ_{\rm res} = 1.1'' \times 1.1''$. CHAMPS identifies sources via two detection methods, a blind search for high-SNR sources, and a prior-based search involving MIRI detections to identify faint sources. The blind search yields a total of 595 sources down to an SNR $\ge4.5σ$ while the prior catalog yields a total of 3162 source down to an SNR $\ge3σ$, leading to a full sample of 3355 unique objects detected across both catalogs. We identify a unique population of 385 SNR $\ge5σ$ sources across the two catalogs; after excluding 9 likely spurious edge detections we define a robust science sample of 376 sources above $\ge5σ$. These sources have a median redshift of $\langle z_{1.2 \text{ mm}}\rangle = 2.54^{+0.89}_{-1.69}$ based on optical/near-IR/mid-IR photometric redshifts and high-quality spectroscopic redshifts, and hold a median stellar mass of $\langle\log (\rm M_\star/M_\odot)\rangle = 10.79^{+0.42}_{-3.08}$. We have further identified 68/376 ($\sim18\%$) sources as candidate AGN through X-ray, UV-optical, infrared and radio selection techniques.

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arXiv2026

Early steps in the hierarchical assembly of a Milky Way-mass galaxy 1 Gyr after the Big Bang

We report JWST observations of a $z_{\rm spec}=5.196$ compact group of three strongly lensed low-mass galaxies ($M_\star \sim 10^{6-7} M_\odot$ each) whose small line-of-sight velocity offsets (from $-120\pm100$ to $+160\pm110$ km s$^{-1}$) and projected separations ($\sim2$ kpc) suggest that they are undergoing merging. On the basis of abundance-matching arguments, the trio appear to be destined to evolve into a Milky Way-mass galaxy by the present day. Our spectrophotometric analysis suggests that the stellar mass growth of this system is not simply just due to the merging of its components; rather, it is being dramatically enhanced by intense bursts of star formation. Presumably initiated by tidally-induced gas inflows, these star-forming bursts boost the mass growth $2.6\pm0.5$ times that expected in straightforward merging of the existing stellar masses. These spectroscopic observations thus not only demonstrate that hierarchical assembly remains a viable formation channel in the early assembly phases of present-day massive galaxy, but also that interaction-induced bursts of star formation are a major accelerator of this assembly process.

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arXiv2026

DeepDive: Simultaneous Formation of Massive Quiescent Galaxies in High-Redshift Galaxy Overdensities

We report on the spectroscopic confirmation of overdense regions of massive quiescent galaxies (QGs) in the early Universe with JWST/NIRSpec. Based on data from the DeepDive NIRSpec program and archival data from the Dawn JWST Archive, we confirm three QGs in the vicinity of Jekyll & Hyde, a pair of massive QG and a dusty star-forming galaxy, at $z=3.71$ and two QGs around SXDS-27434 at $z=4.01$. According to the analysis of galaxy number density with photometric redshifts, Jekyll & Hyde (SXDS-27434) are in an overdense region, where the number density of galaxies is three (four) times higher than the average in the COSMOS (SXDS) field. SED fitting suggests that most of the QGs follow similar star formation histories and have consistent formation and quenching epochs. The same trend is observed in other proto-clusters hosting QGs that were already identified by ground-based telescopes, indicating that the large-scale environment plays an important role in the formation of QGs. In addition, JWST spectra reveal a broad H$α$ emission line from SXDS-27434 and faint emission lines from other three QGs, which are identified as AGN-driven based on their emission line ratios. The overdensity is also reproduced by the Illustris TNG300 simulation at $z=3.71$, in which the member QGs also have similar quenching epochs. These results are consistent with a scenario in which the large-scale structure enhances merger activity and/or gas accretion and triggers AGN feedback, thereby driving simultaneous formation and quenching of QGs in the overdensity.

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arXiv2026

LEGGOS: Direct abundances of N, O, Ne, S, and Ar in five lensed galaxies at Cosmic Noon

We present direct $T_e$ chemical abundances in five strongly lensed galaxies at Cosmic Noon ($2.481 \leq z \leq 3.625$) using JWST/NIRSpec data from the LEGGOS survey. We measure gas-phase abundances of N, O, S, and Ar in all five galaxies, and Ne in two galaxies. Three galaxies have electron temperature constraints from multiple different ionization zones, and we find that these are broadly consistent with temperature scaling relations observed in both local and high-$z$ galaxies. We find a range of oxygen abundances $8.04 \leq 12+\log(\text{O/H}) \leq 8.79$ (22 -- 126\% $Z_{\odot}$). The ratios of N/O and Ne/O are consistent with trends observed in local galaxies. We do not observe any evidence for significant N enhancement in our sample, though the youngest galaxy in our sample (SGAS-J1050) has a mildly elevated $\log(\text{N/O}) = 1.20 \pm 0.08$, which we suggest may be driven by a population of young massive stars. The ratios of S/O and Ar/O are generally sub-solar, similar to trends observed in other high-$z$ galaxies. We find that the S/O and Ar/O abundances are sub-solar, consistent with enrichment from core-collapse supernovae (CCSNe). Modeling of the star formation histories of the LEGGOS galaxies supports CCSNe enrichment, as each galaxy shows a recent period of star formation lasting $\lesssim 100$ Myr, indicating that type Ia supernovae would not yet have had enough time to contribute significantly to the gas-phase abundances of these galaxies.

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arXiv2026

Toward Unbreaking the Universe: MINERVA Measurements of Color Gradients in Massive Quiescent Galaxies Can Help Ease Too-Early Star Formation Tensions

The discovery of a population of massive, ancient quiescent galaxies within the first 2 Gyr of the Universe's history has led to significant tensions with models of galaxy formation. However, these analyses are often based on slit spectroscopy, which typically captures only the center-most region of these galaxies and, crucially, assumes these cores are representative of the entire galaxy. To illustrate the varying stellar populations present throughout these galaxies, we present an analysis of color gradients in four $z>3$, $\log(M_\star/M_\odot)>11$ quiescent galaxies which previous works have argued are in tension with models. Using medium-band photometry from MINERVA JWST observations, we measure resolved photometry in a series of elliptical annuli out to $0.7^{\prime\prime}$ ($\sim4~R_e$). We find negative color gradients in three galaxies, and for the most extreme color gradient ($Δ(U-V)/ΔR=-0.126\pm0.030~{\rm mag~kpc^{-1}}$), we find the stellar mass is 0.1 dex lower when compared to photometry measured within NIRSpec slits. In the limiting case where these color gradients are entirely driven by age, we find lessened tensions with extreme value statistics models out to $z\sim9.5$, though different stellar population modeling choices also contribute significantly. Ultimately, these findings highlight the need for integral field unit spectroscopy. Spatially-resolved spectra can provide the evidence needed to break the age--dust--metallicity degeneracy, and reliably separate the effects of the observed color gradients from the effects of different physical modeling assumptions on the formation histories of these galaxies.

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arXiv2026

LEGGOS I: The JWST LEGGOS Survey -- LEnsing and Galaxy Growth: Observing Substructures -- Unpacks the Nature of Clumpy Star Formation and Quenching in Gravitationally Lensed Galaxies beyond Cosmic Noon

We present first results from the JWST LEGGOS Survey (LEnsing and Galaxy Growth: Observing Substructures), aimed at studying the physics of clumpy star formation and quenching in eight lensed galaxies at $z\sim2$--4. LEGGOS combines multiple Cycle 2 JWST GO programs (GO 4125, GO 3843) and Cycle 1 archival data, and utilizes strong gravitational lensing with NIRCam imaging and NIRSpec integral-field spectroscopy. LEGGOS targets UV-bright, highly magnified systems to resolve $\sim$10--200 pc regions in both rest-frame optical continuum and nebular emission. This overview paper describes the survey design, data reduction and calibration strategy, and science-quality data products, and highlights early examples demonstrating how spectroscopy breaks key degeneracies inherent to photometry-only clump studies, including identifying recent quenching in previously-thought UV star forming galaxies. We introduce a uniform analysis framework that jointly models lensing reconstruction, multi-band photometry, and integral field spectroscopy to disentangle multiple stellar populations within individual clumps and their surrounding diffuse regions. Using maps of Balmer recombination lines and key emission line diagnostic ratios, we connect star formation histories, dust attenuation, and nebular conditions on sub-kpc scales -- LEGGOS galaxies range from uniform metallicities across the whole galaxy, to having higher clump metallicities and harder ionization conditions relative to diffuse regions. The full survey dataset, with simultaneous flux and morphology constraints on clumpy source-plane regions, and a flexible spectrophotometric SPS modeling approach, provides a direct bridge between parsec-scale star formation physics and galaxy assembly at and beyond cosmic noon, offering a robust and efficient means of resolving star formation in the first galaxies.

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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.

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arXiv2026

CANUCS/Technicolor Data Release 2: A Catalogue of Galaxy Structural Parameters in up to 29 HST+JWST bands and a Multi-Wavelength Exploration of the Galaxy Size-Mass Relation at $0.6 < z \leq 4$

We present James Webb Space Telescope (JWST) results of a morphological study of galaxies in the CAnadian NIRISS Unbiased Cluster (CANUCS) and Technicolor surveys, observed in 19 medium- and broadband NIRCam filters in five CANUCS NIRCam Flanking Fields with rest-frame wavelength coverage between $\sim 0.2 - 3.2μm$. Using GALFIT, we measure the morphological parameters of $\sim$ 4,100 star-forming galaxies at $0.6 < z \leq 4$ with stellar masses of $8.5 < \text{log}(M_*/M_\odot) \leq 11.5$. This enables us to concurrently examine how galaxy size varies as a function of stellar mass, redshift, and rest-frame wavelength to provide a novel parametrization of the galaxy size-wavelength relation. Additionally, we analyze the evolution of the galaxy size-mass relation in the rest-frame optical and NIR with the introduction of wavelength as a free parameter. We report a gradient in the slope of the size-mass relation with respect to rest-frame wavelength with a critical crossover mass at $\sim 10^{9.5} M_\odot$. We propose this characteristic mass as the stellar mass at which galaxies transition between diffuse and compact morphologies. We concurrently present the data release of morphological measurements of the five CANUCS-Technicolor NIRCam Flanking Fields in which we provide structural parameters for $\sim$ 41,000 galaxies in up to 29 JWST+HST filters.

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arXiv2026

A Population of Red Galaxies with Very Strong Emission Lines at $z > 5$ Revealed by the NIRCam Medium Bands: ''Classic'' LRDs, Dusty Star-Forming Galaxies, and a Missing Population of LRDs

The NIRCam medium-bands have proven to be efficient at identifying Emission Line Galaxies (ELGs) with high equivalent width (EW) H$α$ and [OIII]+H$β$ emission lines. In this paper we exploit this efficiency to identify a sample of ELGs at $4.9 \lesssim z \lesssim 8.9$ using medium-band imaging from the CANUCS, Technicolor, and JUMPS surveys. We find that the ELGs exhibit a strong correlation between continuum color and emission line strength, such that galaxies with bluer UV/optical continua have stronger H$α$ and [OIII]+H$β$ emission lines. We identify 26 galaxies that are outliers from this relation, which we call the Red Emission line Galaxies (REGs), because of their red continuum color and strong emission lines. We classify the REGs into three categories: 1) ''classic'' Little Red Dots (LRDs) selected with common literature criteria, 2) extended REGs, resolved in F444W and consistent with being Dusty Star Forming Galaxies (DSFGs), and 3) compact REGs, unresolved in F444W but not classified as LRDs. The compact REGs fail common LRD selections for several reasons, including faint continuua, contamination from emission lines (very strong [OIII]+H$β$), and UV/optical colors that are flatter than those of LRDs. We conclude that the compact REGs are likely LRDs that ''classic'' selection criteria miss, and are therefore missing from existing samples. Our results suggest that medium-band selection can provide more complete samples of these objects.

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arXiv2026

MAGAZ3NE: Spatially Resolved Ages and Chemical Abundances of Ultra-Massive Quiescent Galaxies at z $\sim$ 3.5 using JWST/NIRSpec IFU

We present spatially-resolved measurements of stellar age, [Fe/H], and [$α$/Fe] in three ultra-massive ($\rm{log(M_{\ast}/M_{\odot})>11}$), compact ($\rm{R_e} \lesssim 2$ kpc) quiescent galaxies at $z\sim3.5$ using JWST/NIRSpec IFU spectroscopy. These observations provide the first spatially-resolved constraints on $α$-enhancement at this epoch, enabling a direct test of quenching mechanisms before late-time assembly processes such as mergers can erase chemical signatures. The central regions of all three galaxies show both uniformly young ages ($\approx0.6-0.7$ Gyr) and elevated [$α$/Fe] ($\approx0.2-0.5$), indicating rapid, enhanced star formation shortly before recent quenching. Beyond the cores, two galaxies display positive age gradients and negative [$α$/Fe] gradients, consistent with rapid merger-driven quenching, while the third shows a flat age profile indicative of uniform quenching. The [Fe/H] gradients are also consistent with these trends, though we note that the metallicities reported by codes using $α$-enhanced models differ significantly ($\approx0.2-0.4$ dex) from those reported using solar-scaled templates. These data demonstrate that quenching pathways are diverse by $z\sim3.5$, with rapid, merger-driven quenching already operating in a subset of massive quiescent galaxies in the first two billion years of cosmic time. Furthermore, these results establish that explicit treatment of $α$-enhancement is essential for interpreting the star-formation histories of the earliest quenched systems.

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