Spatially resolved gas-phase metallicity maps are a crucial element in building our understanding of the chemical evolution of galaxies. We present spatially resolved metallicity maps obtained from NIRISS/WFSS observations in the first work delivering such an analysis of the slitless spectroscopy of multiple galaxies. We investigated the sources of ionization, metallicity, and their relation to star formation in a spatially resolved sense for a sample of eight galaxies: four from JWST-PASSAGE and four from GLASS-JWST ERS. All but one of these galaxies reside in the redshift range 1.9 ≤ z ≤ 2, the outlier being at z = 3.1. Our sample covers a range of 8.0 < log (M ⋆ / M ⊙ ) < 9.5 in terms of stellar mass, 0.2 < log (SFR M ⊙ yr −1 ) < 1.1 in the star formation rate (SFR), and 7.8 < 12 + log(O / H) < 9.0 in the global gas metallicity. To resolve the question of the star formation-AGN separation in the absence of resolved H α +[NII] lines, we present a new SF-demarcation line in the OHNO parameter space, based on MAPPINGS v5.1 publicly available H II region and AGN model grids, with the caveat that these grids partially overlap the OHNO parameter space. We present the mass-metallicity gradient relation for our sample, which show no clear trend with stellar mass. This might be because the high- z galaxies have not yet started their accretion-dominated evolutionary phase. By interpreting the correlation between spatially resolved metallicity and SFR maps as a proxy for effective timescales of metal-transport in galaxies, we find a possible trend that sees this timescale increasing with stellar mass. This is consistent with the picture of more effective feedback in lower mass galaxies and where massive galaxies generally tend to have longer characteristic timescales.

Resolved metallicity studies of local disc galaxies have revealed that their interstellar media (ISMs) are far from chemically homogeneous, displaying significant (similar to 0.05 dex) variations in the metallicity on characteristic scales of a few hundred parsecs. Such data is at odds with most analytical models, where the ISM is predicted to be more well-mixed. Here, we suggest that the observed small-scale features seen in galaxies may be superbubbles of metal-enriched gas created by a collection of core collapse supernovae with tight spatial (and temporal) correlation. In this scenario, the size of the metallicity fluctuations (superbubble radius, phi) is set by the disc scale height of the galaxy in question (after which point shock breakout favours preferential expansion along directions perpendicular to the dense disc), and the amount of additional metals contained within a fluctuation is proportional to the star formation efficiency in superbubble regions (epsilon). To test this theory, we analysed metallicity maps from the PHANGS-MUSE sample of galaxies using a geostatistical forward-modelling approach. We find phi similar or equal to 300 pc and epsilon = 0.1- 0.2 , in good agreement with our theoretical model. Further, these small-scale parameters are found to be related to the global galaxy properties, suggesting that the local structure of the ISM of galaxies is not universal. Such a model of star formation paints a new picture of galaxy evolution in the modern universe: in large local galaxies, star formation appears steady and regular when averaged over large scales. However, on small scales, these large galaxies remain intrinsically bursty like their smaller, high-redshift counterparts.

In this work we investigate the potential of a thermal infrared (IR) space telescope to remotely characterize the component temperatures of a satellite. With the rapid increase in the number of objects launched in recent years, the ability to detect, track, identify and determine the intent of satellites has become of increasing importance. Spectral modeling of satellites from multi-wavelength photometry in the thermal IR is a technique that has the potential to derive information about the temperature and operational status of a satellite in orbit, without the requirement to spatially resolve the target. Previous work has focused on determination of a single/effective temperature for a Resident Space Objects (RSOs)-such as satellites, asteroids, debris and rocket bodies-from remote observations, obtaining mixed results in terms of ability to classify objects. To progress, we explore a two-greybody component spectral model. Using this analytical model, we investigate which temperature characteristics may be identified from unresolved multi-wavelength photometric observations as a function of the signal-to-noise ratio, under the assumption of Poisson noise-dominated data. With this instrument-agnostic framework, we then quantify the potential of this model to discriminate between RSOs with a single temperature (e.g. natural rocks) versus human-made satellites with a chassis and deployed solar panels where significant component temperature differences exist under typical orbital configurations. Last, we comment on promising prospects of this model for applications to existing and future space telescope observations to characterize RSOs from spatially unresolved photometry. (c) 2025 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

From the turbulent interstellar medium to the cosmic web, astronomers in many different fields have needed to make sense of spatial data describing our Universe. Through different historical choices for mathematical conventions, many different subfields of spatial data analysis have evolved their own language for analysing structures and quantifying correlation in spatial data. Because of this history, terminology from a myriad of different fields is used, often to describe two data products that are mathematically identical. In this Note, we define and describe the differences and similarities between the power spectrum, the two-point correlation function, the covariance function, the semivariogram, and the structure functions, in an effort to unify the languages used to study spatial correlation. We also highlight under which conditions these data products are useful and describe how the results found using one method can be translated to those found using another, allowing for easier comparison between different subfields' native methods. We hope for this document to be a “Rosetta Stone" for translating between different statistical approaches, allowing results to be shared between researchers from different backgrounds, facilitating more cross-disciplinary approaches to data analysis.

We measured the spectral properties of a sample of 20 galaxies at z similar to 0.35 selected for having surprisingly red JWST/NIRCAM F200W-F444W colors. Of these, 19 galaxies were observed with JWST/NIRSpec in the PRISM configuration, while the remaining galaxy was observed with the high-resolution gratings. Of the 20 galaxies in our sample, 17 exhibit strong 3.3 mu m polycyclic aromatic hydrocarbon (PAH) emission (equivalent width (EW) (PAH(3.3)) >= 0.03 mu m). In these galaxies, the strength of the color excess does not depend on environment and correlates with EW(PAH(3.3)). Nonetheless, the presence of the PAH(3.3) alone cannot fully explain the color excess, as an EW of similar to 0.1 mu m is able to increase the color of galaxies by only 0.13 mag. A contribution from a hot dust component is required to explain the excess. Both the PAH(3.3) EW and flux correlate with the H alpha EW and flux, suggesting that they are produced by the same mechanism. Five of the galaxies of our sample showing PAH(3.3) would be classified as passive based on broadband rest frame colors ((B-V) and/or UVJ diagrams) and are hence "faux passive". Of these, three galaxies have a significantly lower EW(PAH(3.3)) given their color and also have low EW(H alpha), and we tentatively conclude that this behavior is due to the presence of an active galactic nucleus. The three galaxies with no PAH(3.3) in emission have passive spectra, as do the eight galaxies in our sample with normal F200W-F444W colors. We therefore conclude that the PAH(3.3) feature is linked to dust-enshrouded star formation. The dust-corrected star formation rate (SFR) from PAH(3.3) is a factor of 3.5 higher than the SFR obtained from H alpha, suggesting that these galaxies are characterized by significant amounts of dust.

We introduce the Bias-free Extragalactic Analysis for Cosmic Origins with NIRCam (BEACON) survey, a JWST Cycle 2 program allocated up to 600 pure-parallel hours of observations. BEACON explores high-latitude areas of the sky with JWST/NIRCam over ∼100 independent sight lines, totaling ∼0.3 deg ^2 , reaching a median F444W depth of ≈28.2 AB mag (5 σ ). Based on existing JWST observations in legacy fields, we estimate that BEACON will photometrically identify 25–150 galaxies at z > 10 and 500–1000 at z ∼ 7–10 uniquely enabled by an efficient multiple filter configuration spanning 0.9–5.0 μ m. The expected sample size of z > 10 galaxies will allow us to obtain robust number density estimates and to discriminate between different models of early star formation. In this paper, we present an overview of the survey design and initial results using the first 19 fields. We present 129 galaxy candidates at z ≳7 identified in those fields, including 11 galaxies at z ≳10 and several UV-luminous ( M _UV < −21 mag) galaxies at z ∼ 8. The number densities of z < 13 galaxies inferred from the initial fields are overall consistent with those in the literature. Despite reaching a considerably large volume (∼10 ^5 Mpc ^3 ), however, we find no galaxy candidates at z > 13, providing us with a complimentary insight into early galaxy evolution with minimal cosmic variance. We publish imaging and catalog data products for these initial fields. Upon survey completion, all BEACON data will be coherently processed and distributed to the community along with catalogs for redshift and other physical quantities.

The electron density ( n e ) of the interstellar medium (ISM) in star-forming galaxies is intimately linked to star formation and ionization condition. Using the high-resolution spectra obtained from the JWST Near-Infrared Spectrograph (NIRSpec) microshutter assembly (MSA) as part of the GLASS-JWST program, we have assembled the largest sample to date (34 galaxies) with individual n e measurements derived from the [O ii ] λλ 3726, 29 and/or [S ii ] λλ 6718, 32 doublets at 0.7 ≲ z ≲ 9.3. The gravitational lensing magnification by the foreground A2744 cluster allows us to probe n e in galaxies with stellar masses ( M * ) down to ≃10 7.5 M ⊙ across the entire redshift range. Our analysis reveals that the [O ii ] flux ratios are marginally anticorrelated with a specific star formation rate (sSFR) within a 1 σ confidence interval, whereas the [S ii ] flux ratios show no significant correlation with sSFR. Despite a clear correlation between sSFR and redshift within our sample, we find no apparent redshift evolution of n e at z ≃ 1–9. Our data set also includes 13 galaxies where n e can be measured from both [O ii ] and [S ii ]. Contrary to findings at lower redshifts, we observe considerable scatter in n e measurements from [O ii ] and [S ii ], indicating a complex gaseous environment with significant variations in n e in high-redshift galaxies. This work highlights the unique capability of JWST NIRSpec/MSA high-resolution spectroscopy to characterize the detailed physical properties of the ISM in individual high-redshift galaxies.

Pair-instability supernovae (PISNe) have long been predicted to be the final fates of near-zero-metallicity very massive stars (Z<Z(circle dot)/3, M-ZAMS greater than or similar to 140M(circle dot)). However, no definite PISN has been observed to date, leaving theoretical modelling validation open. To investigate the observability of these explosive transients, we combine detailed stellar evolution models for PISNe formation, computed from the Binary Population and Spectral Synthesis code suite, BPASS, with the star formation history of all individual computational elements in the Illustris-TNG simulation. This allows us to compute comic PISN rates and predict their host galaxy properties. Of particular importance is that IllustrisTNG galaxies do not have uniform metallicities throughout, with metal-enriched galaxies often harbouring metal-poor pockets of gas where PISN progenitors may form. Accounting for the chemical inhomogeneities within these galaxies, we find that the peak redshift of PISNe formation is z=3.5 instead of the value of z=6 when ignoring chemical inhomogeneities within galaxies. Furthermore, the rate increases by an order of magnitude from 1.9 to 29 PISN Gpc(-3) yr(-1) at z=0, if the chemical inhomogeneities are considered. Using state-of-the-art theoretical PISN light curves, we find an observed rate of 13.8 (1.2) visible PISNe per year for the Euclid-Deep survey, or 83 (7.3) over the six-year lifetime of the mission when considering chemically inhomogeneous (homogenous) systems. Interestingly, only 12 per cent of helium PISN progenitors are sufficiently massive to power a super-luminous supernova event, which can potentially explain why PISN identification in time-domain surveys remains elusive and progress requires dedicated strategies.

Historically, metallicity profiles of galaxies have been modelled using a radially symmetric, two-parameter linear model, which reveals that most galaxies are more metal-rich in their central regions than their outskirts. However, this model is known to yield inaccurate results when the point-spread function (PSF) of a telescope is large. Furthermore, a radially symmetric model cannot capture asymmetric structures within a galaxy. In this work, we present an extension of the popular forward-modelling python package LENSTRONOMY, which allows the user to overcome both of these obstacles. We demonstrate the new features of this code base through two illustrative examples on simulated data. First, we show that through forward modelling, LENSTRONOMY is able to recover accurately the metallicity gradients of galaxies, even when the PSF is comparable to the size of a galaxy, as long as the data is observed with a sufficient number of pixels. Additionally, we demonstrate how LENSTRONOMY is able to fit irregular metallicity profiles to galaxies that are not well-described by a simple surface brightness profile. This opens up pathways for detailed investigations into the connections between morphology and chemical structure for galaxies at cosmological distances using the transformative capabilities of JWST. Our code is publicly available and open source, and can also be used to model spatial distributions of other galaxy properties that are traced by its surface brightness profile.

Potential contamination from low/intermediate-redshift galaxies, such as objects with a prominent Balmer break, affects the photometric selection of high-redshift galaxies through identification of a Lyman break. Traditionally, contamination is estimated from spectroscopic follow-up and/or simulations. Here, we introduce a novel approach to estimating contamination for Lyman-break galaxy (LBG) samples based on measuring spatial correlation with the parent population of lower redshift interlopers. We propose two conceptual approaches applicable to different survey strategies: a single large contiguous field and a survey consisting of multiple independent lines of sight. For a large single field, we compute the cross-correlation function between galaxies at redshift z similar to 6 and intermediate-redshift galaxies at z similar to 1.3. We apply the method to the CANDELS GOODS-S and XDF surveys and compare the measurement with simulated mock observations, finding that the contamination level in both cases is not measurable and lies below 5.5 per cent (at 90 per cent confidence). For random-pointing multiple field surveys, we measure instead the number count correlation between high-redshift galaxies and interlopers, as a two-point correlation analysis is not generally feasible. We show an application to the LBG samples at redshift z similar to 8 and the possible interloper population at z similar to 2 in the Brightest of Reionizing Galaxies (BoRG) survey. By comparing the Pearson correlation coefficient with the result from Monte Carlo simulations, we estimate a contamination fraction of 62(-39)(+13), percent, consistent with previous estimates in the literature. These results validate the proposed approach and demonstrate its utility as an independent check of contamination in photometrically selected samples of high-redshift galaxies.

James Webb Space Telescope observations have spectroscopically confirmed the existence of galaxies as early as 300 Myr after the Big Bang and with a higher number density than what was expected based on galaxy formation models and Hubble Space Telescope observations. Yet, most sources confirmed spectroscopically so far in the first 500 Myr have rest-frame ultraviolet (UV) luminosities below the characteristic luminosity ( M_UV^* ), limiting the signal-to-noise ratio for investigating substructure. Here we present a high-resolution spectroscopic and spatially resolved study of a bright galaxy ( M UV = −21.66 ± 0.03, ∼ 2M_UV^* ) at a redshift z = 9.3127 ± 0.0002 (510 Myr after the Big Bang) with an estimated stellar mass of (1.6_-0.4^+0.5)× 10^9 M_⊙ , forming 19_-6^+5 solar masses per year and with a metallicity of about one tenth that of solar. The system has a morphology typically associated with two interacting galaxies, with a two-component main clump of very young stars (age less than 10 Myr) surrounded by an extended stellar population (120 ± 20 Myr old, identified from modelling the NIRSpec spectrum) and an elongated clumpy tidal tail. The observations acquired at high spectral resolution identify oxygen, neon and hydrogen emission lines, as well as the Lyman break, where there is evidence of substantial absorption of Lyα. The [O ii ] doublet is resolved spectrally, enabling an estimate of the electron number density and ionization parameter of the interstellar medium and showing higher densities and ionization than in analogues at lower redshifts. We identify evidence of absorption lines (silicon, carbon and iron), with low confidence individual detections but a signal-to-noise ratio larger than 6 when stacked. These absorption features suggest that Lyα is damped by the interstellar and circumgalactic media. Our observations provide evidence of a rapid and efficient build-up of mass and metals in the immediate aftermath of the Big Bang through mergers, demonstrating that there were massive galaxies with several billion stars at early times.

We present an analysis of the galaxy merger rate in the redshift range 4.0<z<9.0 (i.e. about 1.5 to 0.5 Gyr after the Big Bang) based on visually identified galaxy mergers from morphological parameter analysis. Our dataset is based on high-resolution NIRCam JWST data (a combination of F150W and F2000W broad-band filters) in the low-to-moderate magnification (mu<2) regions of the Abell 2744 cluster field. From a parent set of 675 galaxies (M-U is an element of [-26.6,-17.9]), we identify 64 merger candidates from the Gini, M-20 and Asymmetry morphological parameters, leading to a merger fraction f(m )= 0.11 +/- 0.04. There is no evidence of redshift evolution of f(m) even at the highest redshift considered, thus extending well into the epoch of reionization the constant trend seen previously at z less than or similar to 6. Furthermore, we investigate any potential redshift dependent differences in the specific star formation rates between mergers and non-mergers. Our analysis reveals no significant correlation in this regard, with deviations in the studied redshift range typically falling within (1-1.5)sigma from the null hypotesis that can be attributed to sample variance and measurement errors. Finally, we also demonstrate that the classification of a merging system is robust with respect to the observed (and equivalently rest-frame) wavelength of the high-quality JWST broad-band images used. This preliminary study highlights the potential for progress in quantifying galaxy assembly through mergers during the epoch of reionization, with significant sample size growth expected from upcoming large JWST infrared imaging datasets.

We present an analysis of the galaxy merger rate in the redshift range $4.0

We present a measurement of the mass-metallicity relation (MZR) at cosmic noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by the GLASS-JWST Early Release Science program. By combining the power of JWST and the lensing magnification by the foreground cluster A2744, we extend the measurements of the MZR to the dwarf mass regime at high redshifts. A sample of 50 galaxies with several emission lines is identified across two wide redshift ranges of $z=1.8-2.3$ and $2.6-3.4$ in the stellar mass range of $\log{(M_*/M_\odot)}\in [6.9, 10.0]$. The observed slope of MZR is $0.223 \pm 0.017$ and $0.294 \pm 0.010$ at these two redshift ranges, respectively, consistent with the slopes measured in field galaxies with higher masses. In addition, we assess the impact of the morphological broadening on emission line measurement by comparing two methods of using 2D forward modeling and line profile fitting to 1D extracted spectra. We show that ignoring the morphological broadening effect when deriving line fluxes from grism spectra results in a systematic reduction of flux by $\sim30\%$ on average. This discrepancy appears to affect all the lines and thus does not lead to significant changes in flux ratio and metallicity measurements. This assessment of the morphological broadening effect using JWST data presents, for the first time, an important guideline for future work deriving galaxy line fluxes from wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space Station Telescope.

Geostatistical methods are powerful tools for understanding the spatial structure of the metallicity distribution of galaxies, and enable construction of accurate predictive models of the 2D metallicity distribution. However, so far these methods have only been applied to very high spatial resolution metallicity maps, leaving it uncertain if they will work on lower quality data. In this study, we apply geostatistical techniques to high-resolution spectroscopic maps of three local galaxies convolved to eight different spatial resolutions ranging from ~40pc to ~1 kpc per pixel. We fit a geostatistical model to the data at all resolutions, and find that for metallicity maps where small scale structure is visible by eye (with > ~10 resolution elements per Re), all parameters, including the metallicity correlation scale, can be recovered accurately. At all resolutions tested, we find that point metallicity predictions from such a geostatistical model outperform a circularly symmetric metallicity gradient model. We also explore dependence on the number of data points, and find that N > ~100 spatially resolved metallicity values are sufficient to train a geostatistical model that yields more accurate metallicity predictions than a radial gradient model. Finally, we investigate the potential detrimental effects of having spaxels smaller than an individual Hii region by repeating our analysis with metallicities integrated over Hii regions. We see that spaxel-based measurements have more noise, as expected, but the underlying spatial metallicity distribution can be recovered regardless of whether spaxels or integrated regions are used.

Potential contamination from low/intermediate-redshift galaxies, such as objects with a prominent Balmer break, affects the photometric selection of high-redshift galaxies through identification of a Lyman break. Traditionally, contamination is estimated from spectroscopic follow-up and/or simulations. Here, we introduce a novel approach to estimating contamination for Lyman-break galaxy (LBG) samples based on measuring spatial correlation with the parent population of lower redshift interlopers. We propose two conceptual approaches applicable to different survey strategies: a single large contiguous field and a survey consisting of multiple independent lines of sight. For a large single field, we compute the cross-correlation function between galaxies at redshift $z \sim 6$ and intermediate-redshift galaxies at $z \sim 1.3$. We apply the method to the CANDELS GOODS-S and XDF surveys and compare the measurement with simulated mock observations, finding that the contamination level in both cases is not measurable and lies below $5.5\%$ (at $90\%$ confidence). For random-pointing multiple field surveys, we measure instead the number count correlation between high-redshift galaxies and interlopers, as a two-point correlation analysis is not generally feasible. We show an application to the LBG samples at redshift $z \sim 8$ and the possible interloper population at $z \sim 2$ in the Brightest of Reionizing Galaxies (BoRG) survey. By comparing the Pearson correlation coefficient with the result from Monte Carlo simulations, we estimate a contamination fraction of $62^{+13}_{-39}\%$, consistent with previous estimates in the literature. These results validate the proposed approach and demonstrate its utility as an independent check of contamination in photometrically selected samples of high-redshift galaxies.

Models of chemical enrichment and inhomogeneity in high-redshift galaxies are challenging to constrain observationally. In this work, we discuss a novel approach to probe chemical inhomogeneities within long Gamma-Ray Burst (GRB) host galaxies, by comparing the absorption metallicity, Zabs, from the GRB afterglow (which probes the environment along the line of sight) with the emission-line metallicity, Zemiss, measured via slit spectroscopy. Using the IllustrisTNG simulation, the theoretical relationship between these metallicity metrics is explored for a range of GRB formation models, varying the GRB progenitor metallicity threshold. For galaxies with fixed Zemiss, the median value of Zabs depends strongly on the GRB progenitor threshold metallicity, with Zabs significantly lower than Zemiss for high metallicity hosts. Conversely, at fixed Zabs, the median value of Zemiss depends primarily on the metallicity distribution of galaxies in IllustrisTNG and their chemical inhomogeneities, offering a GRB-model-independent way to constrain these processes observationally. Currently, only one host galaxy has data for both absorption and emission metallicities (GRB121014A). We re-analyse the emission spectrum and compare the inferred metallicity Zemiss to a recent Bayesian determination of Zabs, finding log(Zemiss/Z ) = log(Zabs/Z ) + 0.35+0.14 −0.25, within ∼ 2 standard deviations of predictions from the IllustrisTNG simulation. Future observations with the James Webb Space Telescope will be able to measure Zemiss for 4 other GRB hosts with known Zabs values, using ∼ 2 hour observations. While small, the sample will provide preliminary constraints on the Zabs − Zemiss relation to test chemical enrichment schemes in cosmological simulations.

In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity L * (refs. 1 , 2 ) do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however, they are surrounded by neutral gas that prevents the escape of the Lyman-α photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744 (ref. 3 ), and a photometric redshift of z ≈ 10. Here we report the spectroscopic confirmation of this very low luminosity (≈0.05 L *) galaxy at z = 9.79, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple ≳4 σ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy ( M UV = −17.35)—with a luminosity typical of the sources responsible for cosmic reionization—has a compact (≈150 pc) and complex morphology, low stellar mass (10 7.19 M ⊙ ) and subsolar (≈0.6 Z ⊙ ) gas-phase metallicity.

Abstract JWST observations confirmed the existence of galaxies as early as 300 million years and with a higher number density than what was expected based on galaxy formation models and Hubble Space Telescope observations. Yet, sources confirmed spectroscopically so far in the first 500 million years have estimated stellar masses below 5×108 M⊙, limiting the signal to noise ratio for investigating substructure. Here, we present a high-resolution spectroscopic and spatially resolved study of a rare bright galaxy at a redshift z = 9.3127±0.0002 (525 million years after the Big Bang) with an estimated stellar mass of (2.5+0.7 −0.5) × 109 M⊙, forming 25+3 −4 Solar masses per year and with a metallicity of about one tenth of Solar - lower than in the local universe for the stellar mass but in line with expectations of chemical enrichment in galaxies 1-2 billion years after the Big Bang. The system has a morphology typically associated to two interacting galaxies, with a two-component main clump of very young stars (age less than 10 million years) surrounded by an extended stellar population (130 ± 20 million years old, identified from modeling of the NIRSpec spectrum) and an elongated clumpy tidal tail. The observations acquired at high spectral resolution identify oxygen, neon and hydrogen emission lines, as well as the Lyman break, where there is evidence of substantial absorption of Lyα. The [O II] doublet is resolved spectrally, enabling an estimate of the electron number density and ionization parameter of the interstellar medium and showing higher densities and ionization than in analogs at lower redshifts. For the first time at z > 8, we identify evidence of absorption lines (silicon, carbon and iron), with low confidence individual detections but signal-to-noise ratio larger than 6 when stacked. These absorption features suggest that Lyα is damped by the interstellar and circumgalactic medium. Our observations provide evidence of rapid and efficient built up of mass and metals in the immediate aftermath of the Big Bang through mergers, demonstrating that massive galaxies with several billion stars are present at earlier times than expected.