arXiv subjects

Marco Chiaberge

Publications and source records attributed to Marco Chiaberge.

At least 19 recordsLinked to original sources

arXiv2026

No evolution in the number density of little red dots from cosmic dawn to cosmic noon

We present our search for little red dots (LRDs) in the "J1030 field", a region of the sky around the $z\sim 6.3$ quasar SDSS J1030+0524, observed by the JWST EIGER program. Over 154 point-like sources selected in a JWST-based photometric catalog, we find five broad line emitters (with $FWHM \gtrsim 1000\ \rm km s^{-1}$) that are red ($F200W - F356W > 0$) and are undetected in the X-rays. We use these sources to derive the bolometric luminosity function (LF) of LRDs at $z = 2.4$ and $z = 4.5$. At $z = 2.4$, the space density of LRDs is only a factor of $\sim 2$ lower than that of all pre-JWST active galactic nuclei (AGNs) with bolometric luminosity $L_{\rm bol} \gtrsim 3 \times 10^{44}\ \rm erg\ s^{-1}$. At $z = 4.5$, our estimate is consistent with those derived for LRDs based on larger areas of the sky. A similar behaviour is observed in the black hole mass function. More importantly, we study the number density of LRDs from cosmic dawn to cosmic noon. We find that there is no significant evolution in the abundance of LRDs with $L_{\rm bol} \gtrsim 3 \times 10^{44}\ \rm erg\ s^{-1}$ at $z > 2$. We speculate that the drop at $z < 4$ seen by other studies is due to their sampling of only the bright-end of the LRDs LF. At cosmic noon, the abundance of LRDs is $n = 3.4^{+5.6}_{-2.4} \times 10^{-5}\ \rm Mpc^{-3}$, which is a factor of $\sim 350$ larger than recent model predictions and is comparable with that of X-ray selected AGNs with similar bolometric luminosity. Our result may imply that, if LRDs are the early, rapid stages of supermassive black hole growth, as suggested by some models, then the formation of black hole seeds can be efficient down to epochs as recent as cosmic noon. Alternatively, LRDs may simply be a high-accretion phase in already mature black holes.

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arXiv2026

A recoiling supermassive black hole in a powerful quasar

Supermassive black holes (SMBH) are thought to grow through accretion of matter and mergers. Models of SMBH mergers have long suffered the final parsec problem, where SMBH binaries may stall before energy loss from gravitational waves (GW) becomes significant, leaving the pair unmerged. Direct evidence of coalesced SMBH remains elusive. Theory predicts that GW recoiling black holes can occur following a black hole merger. Here we present new and conclusive spectroscopic evidence that both the accretion disk and the broad line region in the spatially offset quasar 3C 186 are blue-shifted by the same velocity relative to the host galaxy, with a line of sight velocity of (-1310 +- 21) km/s. This is best explained by the GW recoil super-kick scenario. This confirmation of the ejection process implies that the final parsec problem is resolved in nature, providing evidence that even the most massive black holes can merge.

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arXiv2026

Vision-Language Model Ensembles Achieve Human-Expert Accuracy for Galaxy Merger Classification

We present a proof-of-concept study demonstrating that an ensemble of Vision--Language Models (VLMs) combined using a Bayesian statistical framework can classify galaxy merger morphologies with accuracy comparable to trained human experts. We deploy 15 VLM classifier configurations, spanning four model architectures (Gemma-4 E2B, Gemma-4 E4B, Qwen2.5-VL, and Qwen3-VL) tested with up to four prompt engineering strategies each. We evaluate their performance against a truth-known sample of 41 VELA+SUNRISE mock galaxy images from Lambrides et al. 2021. The VLM ensemble achieves 83.3\% accuracy on confident classifications (merger probability $p_{\rm M} \ge 0.8$ or $p_{\rm M} \le 0.2$), with 5 misclassified galaxies. The ensemble recovers the population merger fraction to within $0.66σ$ of the truth ($f_{\rm M} = 0.52 \pm 0.09$ vs.\ true value of 0.585). Bayesian weighting improves overall accuracy by 17.1 percentage points over simple majority voting, with sensitivity improving by 29.2 percentage points. The VLM ensemble produces 5 misclassified galaxies (2 false positives, 3 false negatives), comparable to the 6 misclassifications (5 false positives, 1 false negative) reported for human classifiers by Lambrides et al. 2021. The apparent differences in error profiles are not statistically significant given the sample size of 41 galaxies. VLMs also produce more moderate per-galaxy merger probability distributions (27\% uncertain) than the more polarized human distributions (15\% uncertain), though this difference is also consistent with statistical fluctuation. These results establish VLMs as scalable, reproducible alternatives to human classifiers within a Bayesian probabilistic merger-fraction framework, with direct applications to large galaxy samples from current and future surveys.

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arXiv2026

The GlimmIr: Spectroscopic Variability in a z~7 LRD Indicates Rapid Changes in Both the Narrow and Broad Line Regions

The enigmatic population of ``Little Red Dots'' (LRDs) sit at the center of some of the largest debates in extragalactic astronomy today. The source(s) of ionizing emission and the physical scale over which it governs is still largely unknown. We show for the first time spectroscopic variability in a z ~ 7 LRD. Comparing a recently obtained 10.2 hr JWST/NIRSpec F290LP/G395M spectrum via the C3PO survey to an 8.4 hr F290LP/G395M spectrum taken 99 days earlier (~13 rest-days) via the THRILS survey, we find a ~30% $ difference in the continuum and broad-line flux, and a 42% difference between [OIII]5008 flux in the two epochs. Through rigorous testing, we confirm that such differences are not the result of differing MSA slit placements on source nor merely flux calibration offsets. These results are further corroborated by both a similar continuum and [OIII]5008 flux differences found in NIRSpec prism/clear observations of the source at an epoch taken approximately a year earlier than the THRILS observations via RUBIES and an additional observation fortuitously taken during the THRILS epoch (within a rest-day) via the CAPERS survey. Assuming LRDs are a type of accreting black hole system, this implies direct sight-lines must exist from the accretion disk to the surrounding nebular gas on scales beyond the broad-line region, and thus any high-density gas interpretations must allow for covering fractions < 100%. Furthermore, these results show the [OIII] line emission is likely not galaxy process-dominated, with a significant population of the narrow-line emitting gas closest to the broad-line region being directly ionized by the LRD. Finally, these results highlight the need for new approaches in inferring black hole properties of these systems, accounting for the lack of significant ionization via star formation, and/or exploring more exotic host-galaxy conditions at these early epochs.

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arXiv2026

The case for super-Eddington accretion in JWST broad-line AGN during the first billion years

A multitude of JWST studies reveal a surprising over-abundance of over-massive accreting super-massive black holes (SMBHs) -- leading to a deepening tension between theory and observation in the first billion years of cosmic time. Across X-ray to infrared wavelengths, models built off of pre-JWST predictions fail to easily reproduce observed AGN signatures (or lack thereof), driving uncertainty around the true nature of these sources. Using a sample of JWST AGN identified via their broadened H$α$ emission and covered by the deepest X-ray surveys, we find neither any measurable X-ray emission nor any detection of high-ionization emission lines frequently associated with accreting SMBHs. We propose that these sources are accreting at or beyond the Eddington limit, which reduces the need for efficient production of heavy SMBH seeds at cosmic dawn. Using a theoretical model of super-Eddington accretion, we can produce the observed relative dearth of both X-ray and ultraviolet emission, as well as the high Balmer decrements, without the need for significant dust attenuation. This work indicates that super-Eddington accretion is easily achieved through-out the early Universe, and further study is required to determine what environments are required to trigger this mode of black hole growth.

astro-ph.HE↗

arXiv2026

Radio selection of heavily obscured AGN in the J1030 field: unraveling a missing Compton-thick population

We tested the effectiveness of radio selection to discover heavily obscured AGNs, particularly at high-z, and we measured their abundance for the first time from a radio perspective. We consider the radio sources detected in the J1030 field, which is one of the fields with the deepest combination of 1.4 GHz radio and X-ray observations. We defined a radio excess parameter as the ratio between the star formation rate (SFR) that would correspond to the observed radio luminosity and the one directly derived from the spectral energy distribution (SED) fitting, $\rm REX=SFR_{1.4GHz}/SFR^{corr}_{SED}$. We then select as radio excess AGN those sources with $\rm REX>8.5$, corresponding to a $3σ$ excess above the median value. In this way, we find 145 radio-excess sources falling into the \textit{Chandra} X-ray image footprint but without X-ray detection. From the deep X-ray upper limits, we estimated a lower limit to the obscuration of each radio-excess AGN, finding on average $\log (N_H/\rm{cm^{-2}})>23.7$. A CTK AGN scenario is also supported by the results of the X-ray stacking analysis performed on sources at $z>1.5$, which revealed X-ray luminosities and hardness ratios compatible with very highly obscured AGN. Finally, we computed the number density of these radio-selected CTK AGN. While at $z\sim 2$ the radio number density agrees well with the CTK AGN predictions of different population synthesis models, at $z\sim3$ the radio selection returns a CTK AGN number density $\sim 2-3$ times larger than what is predicted by the X-ray models and observations. This result supports the effectiveness of radio emission in selecting the most obscured sources, unraveling a population of AGN potentially missed by X-rays surveys at $z>3$, paving the way to a synergistic use of the future radio and X-ray facilities such as the \textit{SKAO} and \textit{NewAthena}.

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arXiv2026

A Nitrogen-rich AGN Powering a Large Ionizing Bubble at z=8.63

We report the detection of Ly$α$ in CANUCS-LRD-z8.6, a recently discovered AGN at z = 8.63 by Tripodi et al. (2024), in new NIRSpec/MSA G140H/F070LP observations. We detect broad Ly$α$ emission (FWHM $= 1540 \pm 260$ km/s) near the systemic velocity, which suggests a large ionizing bubble considering that the universe is almost fully neutral at the redshift. Through Ly$α$ line-shape modeling assuming a Stromgren sphere, we find a large bubble radius, $R_b = 1.5^{+0.3}_{-0.2}$ pMpc, and a moderately high Ly$α$ escape fraction, $f_{esc} = 11 \pm 3$ %. The intrinsic line width is inferred to be broad ($2200 \pm 280$ km/s), likely originating in the broad-line region. Existing data indicate that CANUCS-LRD-z8.6 is within a mild overdensity, $δ= 1.8^{+3.0}_{-0.6}$, suggesting that other galaxies in its proximity might have contributed to the formation of the bubble. The high N IV]$λ$1488 / C IV$λ$1548 and N IV]$λ$1488 / O III]$λ$1661 line ratios measured in existing NIRSpec/PRISM data indicate nitrogen enrichment in this metal-poor, low-luminosity AGN. The spectroscopic features are overall similar to other nitrogen-rich galaxies discovered in the literature, such as GN-z11 and GHZ2/GLASSz12. This suggests that CANUCS-LRD-z8.6 may represent one of the evolutionary phases of those nitrogen-rich galaxies.

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arXiv2025

A big red dot at cosmic noon

We report the discovery of a little red dot (LRD), dubbed BiRD ('big red dot'), at $z=2.33$ in the field around the $z=6.3$ quasar SDSSJ1030+0524. Using NIRCam images, we identified it as a bright outlier in the $F200W-F356W$ color vs $F356W$ magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from HeI$λ10830$ and PaG line, both showing a narrow and a broad ($FWHM\gtrsim 2000\ \rm kms^{-1}$) component. The HeI line is affected by an absorption feature, tracing dense gas with HeI column density in the $2^3S$ level $N\sim 0.5-1.2\times 10^{14}\rm cm^{-2}$, depending on the location of the absorber, which is outflowing at the speed of $Δv \sim -830\ \rm kms^{-1}$. As observed in the majority of LRDs, BiRD does not show X-ray or radio emission. The BH mass and the bolometric luminosity, both inferred from the PaG broad component, amount to $M_{\rm BH}\sim 10^8\rm M_{\odot}$ and $L_{\rm bol}\sim 2.9\times 10^{45}\rm ergs^{-1}$, respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, GN-28074 ("Rosetta Stone") at $z=2.26$ and RUBIES-BLAGN-1 at $z=3.1$. The blueshifted HeI absorption detected in all three sources suggests that gas outflows may be common in LRDs. We derive a first estimate of the space density of LRDs at $z<3$ based on JWST data, as a function of $L_{\rm bol}$ and BH mass. The space density is only a factor of $\sim 2-3$ lower than that of UV-selected quasars with comparable $L_{\rm bol}$ and $z$, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend is also observed in terms of BH masses. If, as suggested by recent theories, LRDs probe the very first and rapid growth of black hole seeds, our finding may suggest that the formation of black hole seeds remains efficient at least up to cosmic noon.

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arXiv2025

Mapping feedback signatures in 3C 297: A quasar-host merger at Cosmic Noon

We present a study of quasar host galaxy 3C 297 which is home to a powerful bent-jet radio source suggesting vigorous interaction with a dense ISM and/or jet precession. Archival HST imaging showed interestingly perturbed morphology of the host with a bright ~30 kpc arc feature, extended filamentary structure of line-emitting gas and clumpy blue excess emission co-spatial with the radio hotspots. Our VLT/SINFONI integral-field observations reveal complex, spatially-resolved Hα+[NII] emission in this source. A prominent blue-shifted wing in Hα indicates an ionized gas flow extending out to ~18 kpc from the nuclear region. Combining our SINFONI narrow-Hα data with archival HST/UV and VLA imaging, we map the young stellar population in the host and compare the spatial distribution of star-forming regions with the ionized gas motion and jet structure. In the attempt to characterize the feedback mechanisms in this chaotic system, we suggest that the powerful radio source dominates the feedback with possible contribution from radiation pressure due to AGN accretion. We also propose that the expanding jet cocoon likely shocked the ISM, triggering a kpc-scale ionized gas outflow and new starbursts that enhanced ongoing merger-induced star formation.

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arXiv2025

Metallicity Scatter Originating from Sub-kiloparsec Starbursting Clumps in the Core of a Protocluster at z=7.88

We present new JWST NIRSpec integral field unit (IFU) G395H/F290LP observations of a merging galaxy system at $z=7.88$, part of A2744-z7p9, the most distant protocluster to date. The IFU cube reveals [OIII] emissions in two previously known galaxies (ZD3 and ZD6) and a newly identified galaxy, ZD12, at $z_{\rm spec}=7.8762$. One of the detected \oiii-emitting regions has a detection of the auroral [OIII]4363, line, allowing us to derive a direct metallicity of $\log$(O/H)$+12=7.4\pm0.2$, while metallicities in other regions are measured using strong line calibration methods. We find large deviations within the measured metallicity ($Δ\log {\rm (O/H)}\sim1$), which suggests a fast chemical enrichment from intense star formation and merger-driven growth, as expected in early galaxies. Our analysis shows that metal-poor regions could easily be outshone by more enriched regions, posing a challenge for spectroscopic analysis based on integrated light (i.e., NIRSpec MSA) against identifying metal-free star formation in the early universe. NIRCam imaging reveals seven UV-bright clumps in ZD12, in the range of stellar mass $\log M_*/M_\odot\sim7.6$--8.9. Four of them are unresolved ($< 100$pc) and intensely star-forming ($>30 M_\odot {\rm yr^{-1} kpc^{-2}}$), likely contributing to the scatter in metallicity by producing an ideal environment for rapid chemical cycles. Lastly, we revisit the nature of the host protocluster by including new member galaxies identified here and in the literature, and obtain local overdensity factor $δ=44_{-31}^{+89}$, total halo mass $M_{\rm h} = 5.8_{-0.3}^{+0.2}\times10^{11}\,M_\odot$, and a formal velocity dispersion of $1100\pm500$ km s$^{-1}$.

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arXiv2024

What can we learn from the Nitrogen abundance of High-z galaxies?

We present measurements of the gas-phase Oxygen and Nitrogen abundances obtained by applying the direct method to JWST NIRspec $R\sim1000$ spectroscopy for 6 galaxies at redshift greater than 3. Our measurements are based on rest-frame optical Nitrogen [N II]$_{λ\lambda6548,6583}$ lines and are complemented by 6 additional objects from the literature at $3\leq z \leq 6$. We find that 9 out of 12 objects have values of log(N/O) that are compatible with those found for low-redshift, metal-poor, dwarf galaxies and for HII regions of more luminous local galaxies. However, 3 out of 12 objects have log(N/O) values that are overabundant compared to what is expected on the basis of their Oxygen abundance. We explore a few standard scenarios to explain the observations and conclude that, within the limited statistics available to us, none of them can be definitely excluded even though we prefer dilution by pristine gas infall in between star formation bursts as this is predicted by simulations to take place as a natural part of bursty star formation.

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arXiv2024

Powerful Radio-Loud Quasars are Triggered by Galaxy Mergers in the Cosmic Bright Ages

While supermassive black holes are ubiquitous features of galactic nuclei, only a small minority are observed during episodes of luminous accretion. The physical mechanism(s) driving the onset of fueling and ignition in these active galactic nuclei (AGN) are still largely unknown for many galaxies and AGN-selection criteria. Attention has focused on AGN triggering by means of major galaxy mergers gravitationally funneling gas towards the galactic center, with evidence both for and against this scenario. However, several recent studies have found that radio-loud AGN overwhelmingly reside in ongoing or recent major galaxy mergers. In this study, we test the hypothesis that major galaxy mergers are important triggers for radio-loud AGN activity in powerful quasars during cosmic noon (1 < z < 2). To this end, we compare Hubble Space Telescope WFC3/IR observations of the z > 1 3CR radio-loud broad-lined quasars to three matched radio-quiet quasar control samples. We find strong evidence for major-merger activity in nearly all radio-loud AGN, in contrast to the much lower merger fraction in the radio-quiet AGN. These results suggest major galaxy mergers are key ingredients to launching powerful radio jets. Given many of our radio-loud quasars are blue, our results present a possible challenge to the "blow-out" paradigm of galaxy evolution models in which blue quasars are the quiescent end result following a period of red quasar feedback initiated by a galaxy merger. Finally, we find a tight correlation between black hole mass and host galaxy luminosity for these different high-redshift AGN samples inconsistent with those observed for local elliptical galaxies.

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arXiv2024

Imaging Spectropolarimetry -- A New Observing Mode on the Hubble Space Telescope's Advanced Camera for Surveys

Imaging spectropolarimetry is a new observing mode on the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST) that was commissioned in Cycle 30 and is available to HST observers starting in Cycle 31 (i.e., from 2023). It is a technique that is accessible from ground-based observatories, but the superb spatial resolution afforded by HST/ACS combined with the slitless nature of HST/ACS grism spectroscopy opens up the possibility of studying polarized extended emission in a way that is not currently possible even with Adaptive Optics facilities on the ground. This mode could help to study interesting targets including (but not limited to) QSOs, AGN and Radio Galaxies, ISM Dust Properties, Pre-Planetary Nebulae, Proto-Planetary and Debris Disks, Supernovae/Supernova Remnants, and Solar System objects. This research note presents the preliminary results from the calibration programs used to calibrate imaging spectropolarimetry on HST/ACS.

astro-ph.IM↗

arXiv2024

Variability of extragalactic X-ray jets on kiloparsec scales

Unexpectedly strong X-ray emission from extragalactic radio jets on kiloparsec scales has been one of the major discoveries of Chandra, the only X-ray observatory capable of sub-arcsecond-scale imaging. The origin of this X-ray emission, which appears as a second spectral component from that of the radio emission, has been debated for over two decades. The most commonly assumed mechanism is inverse Compton upscattering of the Cosmic Microwave Background (IC-CMB) by very low-energy electrons in a still highly relativistic jet. Under this mechanism, no variability in the X-ray emission is expected. Here we report the detection of X-ray variability in the large-scale jet population, using a novel statistical analysis of 53 jets with multiple Chandra observations. Taken as a population, we find that the distribution of p-values from a Poisson model is strongly inconsistent with steady emission, with a global p-value of 1.96e-4 under a Kolmogorov-Smirnov test against the expected Uniform (0,1) distribution. These results strongly imply that the dominant mechanism of X-ray production in kpc-scale jets is synchrotron emission by a second population of electrons reaching multi-TeV energies. X-ray variability on the time-scale of months to a few years implies extremely small emitting volumes much smaller than the cross-section of the jet.

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arXiv2024

Heavily Obscured AGN detection: a Radio vs X-ray challenge

In this work, we study the AGN radio detection effectiveness in the major deep extragalactic surveys, considering different AGN obscuration levels, redshift, and AGN bolometric luminosities. We particularly focus on comparing their radio and X-ray detectability, making predictions for present and future radio surveys. We extrapolate the predictions of AGN population synthesis model of cosmic X-ray background (CXB) to the radio band, by deriving the 1.4 GHz luminosity functions of unobscured (i.e. with hydrogen column densities $\log N_{H} <22$), obscured ($22<\log N_{H}<24$) and Compton-thick (CTK, $\log N_{H} >24$) AGN. We then use these functions to forecast the number of detectable AGN based on the area, flux limit, and completeness of a given radio survey and compare it with the AGN number resulting from X-ray predictions. When applied to deep extragalactic fields covered both by radio and X-ray observations, we show that, while X-ray selection is generally more effective in detecting unobscured AGN, the surface density of CTK AGN radio detected is on average $\sim 10$ times larger than the X-ray one, and even greater at high redshifts, considering the current surveys and facilities. Our results suggest that thousands of CTK AGN are already present in current radio catalogs, but most of them escaped any detection in the corresponding X-ray observations. We also present expectations for the number of AGN to be detected by the Square Kilometer Array Observatory (SKAO) in its future deep and wide radio continuum surveys, finding that it will be able to detect more than 2000 AGN at $z>6$ and some tens at $z>10$, more than half of which are expected to be CTK.

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arXiv2023

Uncovering a Massive z~7.7 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web

In this letter, we report the discovery of the highest redshift, heavily obscured, radio-loud AGN candidate selected using JWST NIRCam/MIRI, mid-IR, sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio observations and mid-IR photometry, we identify a powerful, radio-loud (RL), growing supermassive black hole (SMBH) with significant spectral steepening of the radio SED ($f_{1.28 \mathrm{GHz}} \sim 2$ mJy, $q_{24μm} = -1.1$, $α_{1.28-3\mathrm{GHz}}=-1.2$, $Δα= -0.4$). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of AGN contribution to the UV/optical/NIR data and thus infer heavy amounts of obscuration (N$_{\mathrm{H}} > 10^{23}$ cm$^{-2}$). Using the wealth of deep UV to sub-mm photometric data, we report a singular solution photo-z of $z_\mathrm{phot}$ = 7.7$^{+0.4}_{-0.3}$ and estimate an extremely massive host-galaxy ($\log M_{\star} = 11.4 -12\,\mathrm{M}_{\odot}$) hosting a powerful, growing SMBH (L$_{\mathrm{Bol}} = 4-12 \times 10^{46}$ erg s$^{-1}$). This source represents the furthest known obscured RL AGN candidate, and its level of obscuration aligns with the most representative but observationally scarce population of AGN at these epochs.

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arXiv2023

Enhanced Sub-kpc Scale Star-formation: Results From A JWST Size Analysis of 341 Galaxies At 5<z<14

We present a comprehensive search and analysis of high-redshift galaxies in a suite of nine public JWST extragalactic fields taken in Cycle 1, covering a total effective search area of $\sim358{\rm arcmin^2}$. Through conservative ($8σ$) photometric selection, we identify 341 galaxies at $5 1.5\,σ$ below the derived size-mass slope. These compact sources exhibit a high star formation surface density $Σ_{\rm SFR}>10\,M_\odot\,{\rm yr^{-1}\,kpc^{-2}}$, a range in which only $<0.01\,\%$ of the local star-forming galaxy sample is found. For those with available NIRSpec data, no evidence of ongoing supermassive black hole accretion is observed. A potential explanation for the observed high [OIII]-to-Hbeta ratios could be high shock velocities, likely originating within intense star-forming regions characterized by high $Σ_{\rm SFR}$. Lastly, we find that the rest-frame UV and optical sizes of our sample are comparable. Our results are consistent with these early galaxies building up their structures inside-out and yet to exhibit the strong color gradient seen at lower redshift.

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arXiv2023

The puzzling properties of the MACS1149-JD1 galaxy at z=9.11

We analyze new JWST NIRCam and NIRSpec data on the redshift 9.11 galaxy MACS1149-JD1. Our NIRCam imaging data reveal that JD1 comprises three spatially distinct components. Our spectroscopic data indicate that JD1 appears dust-free but is already enriched, $12 + \log {\rm (O/H) } = 7.90^{+0.04}_{-0.05}$. We also find that the Carbon and Neon abundances in JD1 are below the solar abundance ratio. Particularly the Carbon under-abundance is suggestive of recent star formation where Type~II supernovae have already enriched the ISM in Oxygen but intermediate mass stars have not yet enriched the ISM in Carbon. A recent burst of star formation is also revealed by the star formation history derived from NIRCam photometry. Our data do not reveal the presence of a significant amount of old populations, resulting in a factor of $\sim7\times$ smaller stellar mass than previous estimates. Thus, our data support the view that JD1 is a young galaxy.

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