arXiv subjects

Sandro Tacchella

Publications and source records attributed to Sandro Tacchella.

At least 73 records · Page 4Linked to original sources

arXiv2026

The $z \gtrsim 9$ galaxy UV luminosity function from the JWST Advanced Deep Extragalactic Survey: insights into early galaxy evolution and reionization

The high-redshift UV luminosity function provides important insights into the evolution of early galaxies. JWST has revealed an unexpectedly large population of bright ($M_\mathrm{UV} \lesssim -20$) galaxies at $z\gtrsim10$, implying fundamental changes in the star forming properties of galaxies at increasingly early times. However, constraining the fainter population ($M_\mathrm{UV} \gtrsim -18$) has been more challenging. In this work, we present the $z\gtrsim9$ UV luminosity function from the JWST Advanced Deep Extragalactic Survey. We calculate the UV luminosity function from several hundred $z\gtrsim9$ galaxy candidates that reach UV luminosities of $M_\mathrm{UV}\sim-17$ in redshift bins of $z\sim9-12$ (309 candidates) and $z\sim12-16$ (63 candidates). We search for candidates at $z\sim16-22.5$ and find none. We also estimate the $z\sim14-16$ luminosity function from the $z\geq14$ subset of the $z\sim12-16$ sample. Consistent with other measurements, we find an excess of bright galaxies that is in tension with many theoretical models, especially at $z\gtrsim12$. However, we also find high number densities at $-18\lesssim M_\mathrm{UV} \lesssim-17$, suggesting that there is a larger population of faint galaxies than expected, as well as bright ones. From our parametric fits for the luminosity function, we find steep faint end slopes of $-2.5\lesssimα\lesssim-2.3$, suggesting a large population of faint ($M_\mathrm{UV} \gtrsim -17$) galaxies. Combined, the high normalization and steep faint end slope of the luminosity function could imply that the reionization process is appreciably underway as early as $z=10$.

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arXiv2026

Clumps in High-Redshift Galaxies: Mass Scaling and Radial Trends from JADES

Massive star-forming clumps are a prominent feature of high-redshift galaxies and are thought to trace gravitational fragmentation, feedback, and bulge growth in gas-rich disks. We present a statistical analysis of clumps in $\sim$3600 galaxies spanning $2 \lesssim z \lesssim 8$ from deep JWST/NIRCam imaging in the JADES GOODS--South field. Clumps are identified as residual features after subtracting smooth Sérsic profiles, enabling a uniform, rest-frame optical census of sub-galactic structure. We characterize their physical properties, size--mass relations, and spatial distributions to constrain models of sub-galactic structure formation and evolution. We find that clumps in our sample are typically low-mass ($10^{\sim7-8}M_\odot$), actively star-forming, and show diverse gas-phase metallicity, dust attenuation, and stellar population properties. Their sizes and average pairwise separations increase with cosmic time (toward lower redshift), consistent with inside-out disk growth. The clump mass function follows a power law with slope $α= -1.50_{-0.17}^{+0.19}$, consistent with fragmentation in turbulent disks. We find a deficit of relatively young clumps near galaxy centers and a radial transition in the size--mass relation: outer clumps exhibit steeper, near-virial slopes ($R_{\rm e}\propto M_*^{\sim 0.3}$), while inner clumps follow flatter trends ($R_{\rm e}\propto M_*^{\sim 0.2}$), consistent with structural evolution via migration or disruption. These results provide new constraints on the formation, survival, and dynamical evolution of clumps, highlighting their role in shaping galaxy morphology during the peak of cosmic star formation.

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arXiv2026

An OASIS of Lyman-$α$ within a neutral intergalactic desert: reaffirmed line and blue continuum reveal efficient ionising agents at $z = 13$

$\require{mediawiki-texvc}$Galaxy assembly was already well underway in the first 400 Myr of cosmic time, as recently revealed by JWST. However, the contribution of these early galaxies to cosmic reionisation remains uncertain. Here we present new JWST/NIRSpec observations of GS-z13-1-LA obtained as part of the OASIS and JADES programmes, whose combined deep (56 h) NIRSpec/PRISM spectrum confirms the Lyman-$\mathrmα$ line detection and blue UV continuum at redshift $z = 13.1$ presented in a previous work. The measured Lyman-$\mathrmα$ emission (rest-frame equivalent width of $66_{-9}^{+10}\,Å$) and steep continuum slope ($β_\text{UV} \approx -3$) point towards GS-z13-1-LA hosting a remarkably hot and powerful ionising source, and allow at most a modest contribution from the nebular continuum. The steep turnover of the continuum is still present, but less pronounced in the new OASIS spectrum. Combined, this implies that ionising photons may escape GS-z13-1-LA at a sufficient rate to weaken the other, still undetected UV lines, and to lead the formation of a small ionised bubble ($R_\text{ion} \approx 0.2\,\mathrm{pMpc}$). A yet larger bubble could alleviate the required ionising production efficiency of GS-z13-1-LA from $ξ_\mathrm{ion} \approx 10^{26.4}\,\mathrm{Hz\,erg^{-1}}$ down to $\approx 10^{25.9}\,\mathrm{Hz\,erg^{-1}}$, still extremely high but more readily reconcilable with stellar models. In turn, this would require a notable overdensity of galaxies with highly efficient ionising capabilities, a scenario for which tentative evidence is found in the form of 16 nearby photometric candidates and one spectroscopically confirmed source, JADES-GS-z13-0. The new OASIS observations therefore confirm the overall picture of GS-z13-1-LA as an early beacon of reionisation, providing compelling evidence for its start only 330 Myr after the Big Bang.

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arXiv2026

Out of oxygen: Extremely metal-poor galaxy candidates identified at $2.5 < z < 6.5$ with deep JADES medium-band imaging

JWST is beginning to uncover a population of extremely metal-poor galaxies (EMPGs, $Z < 1\%~\mathrm{Z}_\odot$) at $z > 3$, mostly through serendipitous NIRSpec discoveries and blind slitless spectroscopy. To accelerate our understanding of pristine star formation, we further develop a methodology to identify EMPG candidates from photometry, using the extensive deep medium-band imaging from JADES. Our EMPG candidates at $2.5 < z < 6.5$ exhibit strong photometric boosts by H$α$, yet correspondingly weak boosts by [O III] + H$β$, likely indicating extremely low metallicity to explain their lack of [O III] emission. We further demand our EMPG candidates to have strong Balmer jumps, as revealed by medium-band imaging, to ensure that they are young starbursts, as opposed to broad-line AGN/LRDs, though contamination by dusty/dense-gas starbursts and highly-obscured AGN remains a concern. SED-fitting with near-pristine models (${\sim}0.1$-$1\%~\mathrm{Z}_\odot$) indicates that our 22 EMPG candidates are low-mass (median $M_* \approx 10^{6.7}~\mathrm{M}_\odot$), faint dwarf galaxies ($M_\mathrm{UV} \approx -16.6$), with high ionizing photon production efficiencies ($\log\, (ξ_\mathrm{ion, obs}/\mathrm{(Hz\ erg^{-1})}) \approx 26.0$). Hence these are plausible sites of near-pristine star formation, comprising ${\sim}0.04$-$0.6\%$ of $2.5 < z < 6.5$ galaxies at $-19 < M_\mathrm{UV} < -16$. We discuss this extremely metal-poor extension to the mass-metallicity relation. We forecast that deep (${\sim}28$ h) NIRCam slitless spectroscopy can identify bright EMPGs through strong H$β$ but lack of [O III] emission, or secure the redshifts of fainter systems through H$α$ detections. Highly-multiplexed NIRSpec spectroscopy offers an alternate route to discovering the faintest pristine galaxies out to $z=10$, without requiring deep medium-band/MIRI imaging to identify secure candidates.

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arXiv2026

Diversity and Evolution of Dust Attenuation Curves from Redshift z ~ 1 to 9

The UV-optical dust attenuation curve is key to interpreting the intrinsic properties of galaxies and provides insights into the nature of dust grains and their geometry relative to stars. In this work, we constrain the UV-optical slope of the stellar attenuation curve using a spectroscopic-redshift sample of ~3800 galaxies at z~1-9, to characterize the diversity and redshift evolution of stellar attenuation curves and to gain insight into dust production and evolution at high redshifts. The sample is constructed from three JWST/NIRCam grism surveys in GOODS and A2744 fields, with a wealth of JWST/NIRCam and HST photometry. With constraints from spectroscopic redshifts and emission line fluxes, we use the Prospector SED fitting code with a flexible dust model. We find that the attenuation curve slope varies strongly with Av at all redshifts, becoming flatter at higher attenuation. We find no strong correlation between attenuation curve slope and size or axis ratio, and the trends with stellar mass and star-formation rate are largely driven by their correlation with Av. We find strong evidence that at fixed Av, the curve becomes flatter with increasing redshift. On average, the attenuation curves derived here are shallower than those at z~0 and than the SMC curve. The highest redshift galaxies at z=7-9 (124 galaxies, a significantly larger sample than in previous studies) show slopes even flatter than the Calzetti curve, implying reduced UV obscuration and lower IR luminosities than expected from an SMC dust curve, by as large as an order of magnitude. Hydrodynamical simulations that couple dust growth to gas chemical enrichment successfully reproduce the different loci of high- and low-redshift galaxies in the slope-Av diagram, suggesting that dust in high-redshift galaxies is increasingly dominated by large grains produced in supernova ejecta with limited ISM processing at early times.

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arXiv2026

The Challenge in Illuminating the Invisible: Constraining LyC Escape with Bayesian Modelling and Symbolic Regression

Direct observations of Lyman continuum (LyC) radiation from galaxies during the Epoch of Reionization (EoR) are impeded by absorption in the intergalactic medium, requiring indirect methods to infer the escape fraction of ionizing photons ($f_{\rm esc}^{\rm LyC}$). One approach is to develop and validate such methods on local analogues of the high-redshift galaxies with directly detected LyC leakage. In this study, we constrain $f_{\rm esc}^{\rm LyC}$ using a Bayesian spectral energy distribution (SED) fitting framework built on Prospector, which incorporates a non-parametric star-formation history, a flexible dust attenuation curve, self-consistent nebular emission, and fiber aperture-loss corrections. Our methodology jointly fits broadband photometry and emission line fluxes. We apply six models to the Low-redshift LyC Survey (LzLCS), a sample of local galaxies with physical properties comparable to EoR galaxies, and evaluate them based on their ability to recover the observed flux and their relative Bayesian evidence. The best-performing model is further assessed through a parameter recovery test, demonstrating that $f_{\rm esc}^{\rm LyC}$ can be recovered within uncertainties. Building on these results, we present updated $f_{\rm esc}^{\rm LyC}$ estimates for the LzLCS sample, with a median of 4\%, and values reaching as high as 51\%, with 26 of 64 galaxies having a cosmologically relevant $f_{\rm esc}^{\rm LyC}$($\gtrsim5\%$). Additionally, we present a revised UV $β$-slope vs $\log_{10}(f_{\rm esc}^{\rm LyC})$ relation, derived using symbolic regression with PySR trained on a synthetic dataset generated with \texttt{Prospector}:$\log_{10}(f_{\rm esc}^{\rm LyC}) = (-2.30 \pm 1.28)β- (6.26 \pm 2.91)$, ($σ= 0.43$~dex). The relation successfully reproduces the $f_{\rm esc}^{\rm LyC}$ obtained from full SED fitting of the LzLCS sample within $1σ$.

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arXiv2026

Probing neutral outflows in z ~ 2 galaxies using JWST observations of Ca II H and K absorption lines

Using deep JWST/NIRSpec spectra from the Blue Jay survey, we perform the first systematic investigation of neutral gas content in massive galaxies at Cosmic Noon based on the Ca II H, K absorption lines. We analyze a sample of 9 galaxies at 1.8 < z < 2.8 with stellar masses > 10.6, for which we detect neutral gas absorption both in Ca II and in Na I. After removing the stellar continuum using the best-fit model obtained with Prospector, we fit the excess absorption due to neutral gas in the Ca II H, K doublet and in the Na I D doublet, together with nearby emission lines produced by ionized gas. We measure covering fractions between 0.2 and 0.9 from the Ca II H and K lines, which are spectrally well resolved in the NIRSpec R ~ 1000 observations, unlike the absorption lines in the Na I D doublet. We measure the velocity shift, velocity dispersion, and column density separately for Ca II and Na I. About half of the galaxies present blueshifted Ca II, indicative of an outflow of neutral gas, consistent with previous results based on Na I. The velocity shift and the column density measured from Ca II are correlated with those measured from Na I, implying that these absorption lines trace gas in similar physical conditions. However, the column densities are not in a 1:1 relation, meaning that the relative amount of Ca II and Na I atoms along the line of sight varies with the gas column density. After discussing possible reasons for this behavior, we derive an empirical relation between the column density of Ca II and the column density of Na I and, in a more indirect way, of neutral hydrogen H I. This calibration offers a new way to estimate the outflow mass and the mass outflow rate for the neutral phase from current and future JWST observations of massive galaxies at Cosmic Noon and beyond

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arXiv2026

Filling the Gap in Cluster Evolution: JWST's Glimpse into a Young, Star-Forming Cluster at Cosmic Noon

We present a detailed study of HUDFJ0332.4-2746.6 (HUDF46), a $z \approx 1.84$ overdensity in the Hubble Ultra Deep Field, previously identified with HST as a proto-cluster. JWST/NIRISS spectroscopy expands its confirmed membership from 18 to 37 galaxies, while deep HST/ACS, JWST/NIRCam, and JWST/MIRI imaging provide a comprehensive multiwavelength view from the rest-frame UV to the mid-infrared. This dataset probes the population across three dex in stellar mass ($M_\bigstar \approx 10^{7.5\text{--}10.5}\,M_\odot$), delivering the first direct view of a young cluster down to such low-$M_\bigstar$ at $z\gtrsim1$. Assuming virialization, we derive a velocity dispersion of $σ\approx 670\pm 91\,\mathrm{km\,s^{-1}}$ and a halo mass of $M_{200} \approx (1.2\pm0.2) \times 10^{14}\,M_\odot$, in agreement with X-ray constraints from deep {\it Chandra} data. Despite residing in a massive halo likely in the hot-halo regime, the population is overwhelmingly star-forming, with no established red sequence and no extended X-ray emission from a hot intracluster medium. HUDF46 members have stellar and structural properties nearly indistinguishable from coeval field galaxies, and the structure hosts only one AGN candidate, found in its brightest galaxy, which lies at the cluster center. Overall, HUDF46 appears to be in a transitional phase prior to the onset of environmental quenching, making its galaxy population a key benchmark for tracing the processes that will later build a passive population and shape the assembly of massive clusters at later cosmic times.

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arXiv2026

Characterising Ly$α$ damping wings at the onset of reionisation: Evidence for highly efficient star formation driven by dense, neutral gas in UV-bright galaxies at $z>9$

One of the major conundrums in contemporary extragalactic astrophysics is the apparent overabundance of a remarkable population of UV-bright galaxies at redshifts $z\gtrsim 9$. We analyse galaxies spectroscopically observed by JWST/NIRSpec Prism and confirmed to lie at $z>9$, with sufficient signal-to-noise to carefully model their rest-frame UV to optical continua and line emission. In particular, we model the damped Lyman-$α$ (Ly$α$) absorption (DLA) features of each galaxy to place observational constraints on the gas assembly of neutral atomic hydrogen (HI) onto the galaxy halos at the onset of cosmic reionisation. Based on the derived HI column densities and star-formation rate (SFR) surface densities, we show that all galaxies are highly efficient at forming stars on rapid $\sim 10-100\,$Myr depletion timescales, greatly in excess compared to the canonical local universe Kennicutt-Schmidt relation and predictions from state-of-the-art galaxy formation simulations. The dense HI gas appears to also drive the offset from the fundamental-metallicity relation of these galaxies though its dust-to-gas ratio is seemingly consistent with values derived for local galaxies except for the lowest metallicity sight-lines. Our results provide the first robust observational constraints on the impact of pristine HI gas on early galaxy assembly, and imply that a combination of highly efficient star formation and low dust obscuration can likely explain the UV-brightness of galaxies at cosmic dawn.

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arXiv2026

The THESAN-ZOOM project: Mystery N/O more -- uncovering the origin of peculiar chemical abundances and a not-so-fundamental metallicity relation at $3<z<12$

We present an analysis of metallicities and chemical abundances at $3 -0.6$) without the need for exotic yields in our chemical network. Instead, bursty star formation naturally generates order-of-magnitude excursions in N/O on $\lesssim$100 Myr timescales due to temporally differential galactic winds; after a starburst, stellar feedback expels gas, leaving a large population of asymptotic-giant-branch stars to dominate the enrichment of the relatively low-mass interstellar medium. NRGs lie below the main sequence and typically exhibit $\mathrm{EW}[H$β$]\lesssim40$ Å, in apparent tension with observed high-EW NRGs. This tension is reconciled if observed NRGs are in the initial stages of a subsequent starburst, illuminating previously enriched gas, which is supported by the finding of high SFR surface density nitrogen-rich giant molecular clouds.

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arXiv2026

The THESAN-ZOOM project: Burst, quench, repeat -- unveiling the evolution of high-redshift galaxies along the star-forming main sequence

Characterizing the evolution of the star-forming main sequence (SFMS) at high redshift is crucial to contextualize the observed extreme properties of galaxies in the early Universe. We present an analysis of the SFMS and its scatter in the THESAN-ZOOM simulations, where we find a redshift evolution of the SFMS normalization scaling as $\propto (1+z)^{2.64\pm0.03}$, significantly stronger than is typically inferred from observations. We can reproduce the flatter observed evolution by filtering out weakly star-forming galaxies, implying that current observational fits are biased due to a missing population of lulling galaxies or overestimated star-formation rates. We also explore star-formation variability using the scatter of galaxies around the SFMS ($σ_{\mathrm{MS}}$). At the population level, the scatter around the SFMS increases with cosmic time, driven by the increased importance of long-term environmental effects in regulating star formation at later times. To study short-term star-formation variability, or ''burstiness'', we isolate the scatter on timescales shorter than 50 Myr. The short-term scatter is larger at higher redshift, indicating that star formation is indeed more bursty in the early Universe. We identify two starburst modes: (i) externally driven, where rapid large-scale inflows trigger and fuel prolonged, extreme star formation episodes, and (ii) internally driven, where cyclical ejection and re-accretion of the interstellar medium in low-mass galaxies drive bursts, even under relatively steady large-scale inflow. Both modes occur at all redshifts, but the increased burstiness of galaxies at higher redshift is due to the increasing prevalence of the more extreme external mode of star formation.

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arXiv2026

The THESAN-ZOOM project: central starbursts and inside-out quenching govern galaxy sizes in the early Universe

We explore the evolution of galaxy sizes at high redshift ($3 < z < 13$) using the high-resolution THESAN-ZOOM radiation-hydrodynamics simulations, focusing on the mass range of $10^6\,\mathrm{M}_{\odot} < \mathrm{M}_{\ast} < 10^{10}\,\mathrm{M}_{\odot}$. Our analysis reveals that galaxy size growth is tightly coupled to bursty star formation. Galaxies above the star-forming main sequence tend to form stars in a central starburst, which decreases their radial size. These galaxies quench inside-out, causing spatially extended star formation and increasing their radial size, leading to oscillatory behavior around the size-mass relation. Notably, we find a positive intrinsic size-mass relation at high redshift, consistent with observations but in tension with large-volume simulations. We attribute this discrepancy to the bursty star formation captured by our multi-phase interstellar medium framework, but missing from simulations using the effective equation-of-state approach with hydrodynamically decoupled feedback. We also find that the normalization of the size-mass relation follows a double power law as a function of redshift, with a break at $z\approx6$, because the majority of galaxies at $z > 6$ show rising star-formation histories, and therefore are in a compaction phase. We demonstrate that H$α$ emission is systematically extended relative to the UV continuum by a median factor of 1.7, consistent with recent JWST studies. However, in contrast to previous interpretations that link extended H$α$ sizes to inside-out growth, we find that Lyman-continuum (LyC) emission is spatially disconnected from H$α$. Instead, a simple Strömgren sphere argument reproduces observed trends, suggesting that extreme LyC production during central starbursts is the primary driver of extended nebular emission.

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arXiv2026

Overmassive black holes in the early Universe can be explained by gas-rich, dark matter-dominated galaxies

JWST has revealed the apparent evolution of the black hole (BH)-stellar mass ($M_\mathrm{BH}$-$M_\rm{\ast}$) relation in the early Universe, while remaining consistent with the BH-dynamical mass ($M_\mathrm{BH}$-$M_\mathrm{dyn}$) relation. We predict BH masses for $z>3$ galaxies in the high-resolution THESAN-ZOOM simulations by assuming the $M_\mathrm{BH}$-$M_\mathrm{dyn}$ relation is fundamental. Even without live BH modelling, our approach reproduces the JWST-observed $M_\mathrm{BH}$ distribution, including overmassive BHs relative to the local $M_\mathrm{BH}$-$M_\mathrm{\ast}$ relation. We find that $M_\mathrm{BH}/M_\mathrm{\ast}$ declines with $M_\mathrm{\ast}$, evolving from $\sim$0.1 at $M_\mathrm{\ast}=10^6\,\mathrm{M_\odot}$ to $\sim$0.01 at $M_\mathrm{\ast}=10^{10.5}\,\mathrm{M_\odot}$. This trend reflects the dark matter ($f_\mathrm{DM}$) and gas fractions ($f_\mathrm{gas}$), which decrease with $M_\mathrm{\ast}$ but show little redshift evolution down to $z=3$, resulting in small $M_\mathrm{\ast}/M_\mathrm{dyn}$ ratios and thus overmassive BHs in low-mass galaxies. We use $\texttt{Prospector}$-derived stellar masses and star-formation rates to infer $f_\mathrm{gas}$ across 48,022 galaxies in JADES at $3<z<9$, finding excellent agreement with our simulation. Our results demonstrate that overmassive BHs would naturally result from a fundamental $M_\mathrm{BH}$-$M_\mathrm{dyn}$ relation and be typical of the gas-rich, dark matter-dominated nature of low-mass, high-redshift galaxies. Such overmassive BHs may strongly influence early galaxy formation, and we caution that our approach does not include the self-consistent BH-galaxy co-evolution required for a complete understanding.

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arXiv2026

The density-bounded twilight of starbursts in the early Universe

The peculiar nebular emission displayed by galaxies in the early Universe presents a unique opportunity to gain insight into the regulation of star formation in extreme environments. We investigate 500 (109) galaxies with deep NIRSpec/PRISM observations from the JADES survey at $z>2$ ($z>5.3$), finding 52 (26) galaxies with Balmer line ratios more than $1σ$ inconsistent with Case B recombination. These anomalous Balmer emitters (ABEs) cannot be explained by dust attenuation, indicating a departure from Case B recombination. To address this discrepancy, we model density-bounded nebulae with the photoionisation code CLOUDY. Density-bounded nebulae show anomalous Balmer line ratios due to Lyman line pumping and a transition from the nebulae being optically thin to optically thick for Lyman lines with increasing cloud depth. The H$α$/H$β$ versus H$γ$/H$β$ trend of density-bounded models is robust to changes in stellar age of the ionising source, gas density, and ionisation parameter; however, increasing the stellar metallicity drives a turnover in the trend. This is due to stronger stellar absorption features around Ly$γ$ reducing H$β$ fluorescence, allowing density-bounded models to account for all observed Balmer line ratios. ABEs show higher [OIII]/[OII], have steeper ultra-violet slopes, are fainter, and are more preferentially Ly$α$ emitters than galaxies which are consistent with Case B and little dust. These findings suggest that ABEs are galaxies that have become density bounded during extreme quenching events, representing a transient phase of $\sim$20 Myr during a fast breathing mode of star formation.

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arXiv2026

A Cosmic Miracle: A Remarkably Luminous Galaxy at $z_{\rm{spec}}=14.44$ Confirmed with JWST

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 ($M_{\rm{UV}}=-20.2$) source in the COSMOS field at $z_{\rm{spec}}=14.44^{+0.02}_{-0.02}$ 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 $\sim3σ$ detections of five rest-UV emission lines. The number density of bright $z_{\rm{spec}}\sim14-15$ sources implied by our "Mirage or Miracle" survey spanning $\sim350$ arcmin$^{2}$ is $>100\times$ larger ($182^{+329}_{-105}\times$) than pre-JWST consensus models. The high EWs of UV lines ($\sim15{-}35$ Å) signal a rising star-formation history, with a $\sim10\times$ increase in the last 5 Myr ($\rm{SFR_{\rm{5Myr}}}/\rm{SFR_{\rm{50Myr}}}=9.9^{+3.0}_{-5.8}$). The source is extremely compact (circularized $r_{\rm{e}} = 74^{+15}_{-12}$ 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 $\sim100\%$ 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.

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arXiv2026

When relics were made: vigorous stellar rotation and low dark matter content in the massive ultra-compact galaxy GS-9209 at z=4.66

JWST uncovered a large number of massive quiescent galaxies (MQGs) at $z>3$, which theoretical models struggle to reproduce. Explaining the number density of such objects requires extremely high conversion efficiency of baryons into stars in early dark matter halos. Using stellar kinematics, we can investigate the processes shaping the mass assembly histories of MQGs. We present high-resolution JWST/NIRSpec integral field spectroscopy of GS-9209, a massive, compact quiescent galaxy at $z=4.66$ ($\log (M_{\ast}/M_{\odot})=10.52 \pm 0.06$, $R_{eff}=220 \pm 20$ pc). Full spectral fitting of the spatially resolved stellar continuum reveals a clear rotational pattern, yielding a spin parameter of $λ_{2R_{eff}}=0.85 \pm 0.10$. This study suggests that at least a fraction of the earliest quiescent galaxies were fast rotators and that quenching was a dynamically gentle process, preserving the stellar disc even in highly compact objects. Using Jeans anisotropic modelling and assuming a NFW profile, we measure a dark matter fraction of $f_{DM} (<2R_{eff}) = 14.5^{+6.0}_{-4.2} \% $. Our findings use stellar kinematics to confirm the massive nature of early quiescent galaxies, previously inferred from stellar population modelling. We suggest that GS-9209 has a similar structure to low-redshift `relic' galaxies. However, unlike relic galaxies which have bottom-heavy initial mass functions (IMF), the dynamically inferred mass-to-light ratio of GS-9209 is consistent with a Milky-Way like IMF. The kinematical properties of GS-9209 are different from those of $z<1$ early-type galaxies and more similar to those of recently quenched post-starburst galaxies at $z>2$.

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arXiv2026

JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5: NIRCam Imaging in GOODS-S and GOODS-N

We present the Near Infrared Camera (NIRCam) imaging products of the fifth data release (DR5) of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES). The JADES survey is one of the most ambitious programs yet conducted on JWST, producing deep infrared imaging and multiobject spectroscopy on the GOODS-S and GOODS-N extragalactic deep fields in order to explore galaxies to the earliest epoch. Here we describe the NIRCam data reduction procedures that result in deep and well-characterized mosaics in up to 18 filters covering 469 arcmin$^2$, with 250 arcmin$^2$ having at least 8 filters of coverage. This release contains the full NIRCam imaging of JADES, over 800 JWST mission hours, as well as co-reductions of 19 other programs in these two premier deep fields. We perform detailed tests on the final data products, thereby characterizing the photometric properties, point-spread function, and astrometric alignment. We release mosaics for individual programs (or epochs, depending on scheduling) and the mosaics combining data from all programs in order to facilitate photometric variability studies and the deepest possible photometry.

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arXiv2026

JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5: MIRI Coordinated Parallels in GOODS-S and GOODS-N

Medium to ultra-deep mid-infrared imaging surveys with the James Webb Space Telescope (JWST)'s Mid-Infrared Instrument (MIRI) are reframing our view of the early Universe, from the emergence of ultra-red dusty and quiescent galaxies to the epoch of reionization to the first galaxies. Here we present the MIRI coordinated parallels component of the JADES program, which obtained ultra-deep (155 ks) imaging at $7.7 μ$m over $\sim10$ arcmin$^2$ as well as medium depth ($\sim5-15$ ks) imaging at $7.7, 12.8$, and $15 μ$m over $\sim36$, 25, and 22 arcmin$^2$, respectively, in the GOODS-S and GOODS-N fields. This paper describes the data reduction, which combines the official JWST Calibration Pipeline with custom steps to optimize flagging of warm/hot pixels and optimize background subtraction. We further introduce a new step to address artifacts caused by persistence from saturating sources. The final, fully reduced JADES/MIRI mosaics are being released as part of JADES Data Release 5, along with prior-based forced photometry using NIRCam detection images, providing critical rest-frame near-infrared and optical constraints on early galaxy populations.

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