Understanding when and how galaxies quench their star formation is crucial for understanding the dominant physical processes at play. The spectral energy distribution (SED) of galaxies encodes significant information on their past histories: the relative importance of different physical processes influences the observed distribution of SED shapes in the galaxy population. We use a simulation based inference (SBI) approach to directly constrain the distribution of formation times, quenching times and quenching timescales within the massive galaxy population at z > 2 from their broad band photometric colour distribution at 1.710.3. We measure a quenched galaxy fraction of 0.24+/-0.02, with the number density of quenched galaxies rising rapidly 2.5Gyr after the Big Bang (z< 2.6). Galaxies must quench rapidly to achieve the precise bimodal colour distribution: defining the quenching timescale as the time from peak star formation rate (SFR_peak) -> 0.5xSFR_peak, the quenching timescale distribution has a mode at 97_-25^+31Myr, a median of 182+/-16Myr and a tail to 700Myr. To achieve full quiescence takes a median time of 400Myr. Comparing to direct number density measurements of quenched galaxies at z>2 the combination of recent and rapid quenching inferred from the fossil record suggests a substantial rejuvenation and/or merger rate for quenched galaxies observed directly at z>3.5.

We present the number densities and physical properties of the bright galaxies spectroscopically confirmed at z ∼ 7–14. Our sample is composed of 60 galaxies at z spec ∼ 7–14, including recently confirmed galaxies at z spec = 12.34–14.18 with JWST, as well as new confirmations at z spec = 6.583–7.643 with −24 < M UV < −21 mag using ALMA and Keck. Our JWST/NIRSpec observations have also revealed that very bright galaxy candidates at z ∼ 10–13 identified from ground-based telescope images before JWST are passive galaxies at z ∼ 3–4, emphasizing the necessity of strict screening and spectroscopy in the selection of the brightest galaxies at z > 10. The UV luminosity functions derived from these spectroscopic results are consistent with a double power-law function, showing tensions with theoretical models at the bright end. To understand the origin of the overabundance of bright galaxies, we investigate their morphologies using JWST/NIRCam high-resolution images obtained in various surveys, including PRIMER and COSMOS-Web. We find that ∼70% of the bright galaxies at z ∼ 7 exhibit clumpy morphologies with multiple subcomponents, suggesting merger-induced starburst activity, which is consistent with SED fitting results showing bursty star formation histories. At z ≳ 10, bright galaxies are classified into two types of galaxies: extended ones with weak high-ionization emission lines, and compact ones with strong high-ionization lines including N iv] λ 1486, indicating that at least two different processes (e.g., merger-induced starburst and compact star formation/AGN) are shaping the physical properties of the brightest galaxies at z ≳ 10 and are responsible for their overabundance.

We use JWST/NIRSpec observations from the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics survey to constrain the shape of the nebular attenuation curve of a star-forming galaxy at z = 4.41, GOODSN-17940. We utilize 12 H i recombination lines to derive the attenuation curve spanning optical to near-infrared wavelengths (3751–9550 Å). We then leverage a high signal-to-noise ratio spectroscopic detection of the rest-frame ultraviolet continuum in combination with rest-UV photometric measurements to constrain the shape of the curve at ultraviolet wavelengths. While this UV constraint is predominantly based on stellar emission, the large measured equivalent widths of H α and H β indicate that GOODSN-17940 is dominated by an extremely young stellar population <10 Myr in age such that the UV stellar continuum experiences similar attenuation to that of the nebular emission. The resulting combined nebular attenuation curve spans 1400–9550 Å and has a shape that deviates significantly from commonly assumed dust curves in high-redshift studies. Relative to the Milky Way, SMC, and Calzetti curves, the new curve has a steeper slope at long wavelengths ( λ > 5000 Å) while displaying a similar slope across blue-optical wavelengths ( λ = 3750–5000 Å). In the ultraviolet, the new curve is shallower than the SMC and Calzetti curves and displays no significant 2175 Å bump. This work demonstrates that the most commonly assumed dust curves are not appropriate for all high-redshift galaxies. These results highlight the ability to derive nebular attenuation curves for individual high-redshift sources with deep JWST/NIRSpec spectroscopy, thereby improving the accuracy of physical properties inferred from nebular emission lines.

The advent of the JWST has revolutionized our understanding of high-redshift galaxies. In particular, the NIRCam instrument on-board JWST has revealed a population of red galaxies that had largely evaded detection with Hubble Space Telescope (HST), potentially due to significant dust obscuration, quiescence, or extreme redshift. Here, we present the first NIRSpec spectra of 23 red, HST faint or dark galaxies (H-F444W>1.75), unveiling their nature and physical properties. This sample includes both dusty and quiescent galaxies with spectroscopic data from NIRSpec/PRISM, providing accurate spectroscopic redshifts with z(spec)(& horbar;)=4.1 +/- 0.7. The spectral features demonstrate that, while the majority of red galaxies are dusty, a substantial fraction, 13(-6)(+9 )%, are quiescent. For the dusty galaxies, we have quantified the dust attenuation using the Balmer decrement (H alpha/H beta), finding attenuations AV>2 mag. We find that red dusty galaxies are H alpha emitters with equivalent widths spanning the range 68A & ring;9.8. This pilot NIRSpec programme reveals the diverse nature of HST-dark galaxies and highlights the effectiveness of NIRSpec/PRISM spectroscopic follow-up in distinguishing between dusty and quiescent galaxies and properly quantifying their physical properties. Upcoming research utilizing higher-resolution NIRSpec data and combining JWST with ALMA observations will enhance our understanding of these enigmatic and challenging sources.

With stunning clarity, JWST has revealed the Universe's first billion years. The scientific community is analyzing a wealth of JWST imaging and spectroscopic data from that era, and is in the process of rewriting the astronomy textbooks. Here, 1.5 years into the JWST science mission, we provide a snapshot of the great progress made towards understanding the initial chapters of our cosmic history. We highlight discoveries and breakthroughs, topics and issues that are not yet understood, and questions that will be addressed in the coming years, as JWST continues its revolutionary observations of the Early Universe. While this compendium is written by a small number of authors, invited to ISSI Bern in March 2024 as part of the 2024 ISSI Breakthrough Workshop, we acknowledge the work of a large community that is advancing our collective understanding of the evolution of the Early Universe.

We present an analysis of the rest-frame optical spectra of 22 [O III]lambda 4363 detected galaxies in the redshift range 1.65 <= z <= 7.92 (with (z) = 4.05) from JWST/NIRSpec medium-resolution observations taken as part of the EXCELS survey. To supplement these high-redshift sources, we also consider a sample of 782 local [O III]lambda 4363 detected galaxies from the DESI Early Data Release. Our analysis demonstrates that many strong-line calibrations are biased in the early Universe due to the systematic evolution in ionization conditions with redshift. However, the recently introduced R calibration mostly removes the dependence on ionization state and can be considered a largely redshift-independent calibration. In a similar spirit, we introduce a new strong line diagnostic, RNe (using [O II]lambda lambda 3726,3729, [Ne III]lambda 3869 and H gamma ), which can be used to robustly estimate metallicities when the [O III]lambda 5007 is redshifted out of the wavelength range of JWST/NIRSpec at z > 9.5. We also show that strong-line diagnostics using the [N II]lambda 6584 emission line are likely to be biased at high redshift due to a moderate enhancement in the average N/O abundance ratios (at fixed O/H) in these sources. Finally, we discuss the location of our new [O III]lambda 4363 detected galaxies at z 4 on the mass-metallicity plane and investigate the redshift evolution of the fundamental metallicity relation (FMR). We find tentative evidence for an increasing deviation from the FMR at z > 4, which might indicate fundamental differences in the baryon cycle at these redshifts. However, more data are required as our high-redshift constraints are still based on a relatively small sample of galaxies and the significance of the deviation is strongly dependent on the assumed form of the FMR

We present the results of a study investigating the galaxy stellar-mass function (GSMF), size-mass relations, and morphological properties of star-forming and quiescent galaxies over the redshift range 0.25

Context. One of the surprising early findings with JWST has been the discovery of a strong “roll-over” or a softening of the absorption edge of Lyα in a large number of galaxies at z ≳ 6, in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as strong cumulative damped Lyα absorption (DLA) wings from high column densities of neutral atomic hydrogen (H I), signifying major gas accretion events in the formation of these galaxies. Aims. To explore this new phenomenon systematically, we assembled the JWST/NIRSpec PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 584 galaxies at z = 5.0 − 13.4, designed to study the physical properties and gas in and around galaxies during the reionization epoch. Methods. We characterized this benchmark sample in full and spectroscopically derived the galaxy redshifts, metallicities, star formation rates, and ultraviolet (UV) slopes. We defined a new diagnostic, the Lyα damping parameter DLyα, to measure and quantify the net effect of Lyα emission strength, the H I fraction in the intergalactic medium, or the local H I column density for each source. The JWST-PRIMAL survey is based on the spectroscopic DAWN JWST Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools. All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. Results. We find that the fraction of galaxies showing strong integrated DLAs with NHI > 1021 cm−2 only increases slightly from ≈60% at z ≈ 6 up to ≈65 − 90% at z > 8. Similarly, the prevalence and prominence of Lyα emission is found to increase with decreasing redshift, in qualitative agreement with previous observational results. Strong Lyα emitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Conclusions. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine H I gas accretion. At z = 8 − 10, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed Lyα emission at z < 8.

We present results on the emission-line properties of z = 1.4–7.5 star-forming galaxies in the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) Cycle 1 JWST/NIRSpec program. Based on its depth, continuous wavelength coverage from 1 to 5 μ m, and medium spectral resolution ( R ∼ 1000), AURORA includes detections of a large suite of nebular emission lines spanning a broad range in rest-frame wavelength. We investigate the locations of AURORA galaxies in multiple different emission-line diagrams, including traditional BPT diagrams of [O iii ] λ 5007/H β versus [N ii ] λ 6583/H α , [S ii ] λλ 6717, 6731/H α , and [O i ] λ 6300/H α , and the ionization–metallicity diagram of [O iii ] λ 5007/[O ii ] λ 3727 (O _32 ) versus ([O iii ] λ 5007+[O ii ] λ 3727)/H β ( R _23 ). We also consider a bluer rest-frame ionization–metallicity diagram introduced recently to characterize z > 10 galaxies, [Ne iii ] λ 3869/[O ii ] λ 3727 versus ([Ne iii ] λ 3869+[O ii ] λ 3727)/H δ , as well as longer-wavelength diagnostic diagrams extending into the rest-frame near-IR: [O iii ] λ 5007/H β versus [S iii ] λλ 9069, 9532/[S ii ] λλ 6717, 6731 (S _32 ), and He i λ 1.083 μ m/Pa γ and [S iii ] λ 9532/Pa γ versus [Fe ii ] λ 1.257 μ m/Pa β . With a significant boost in signal-to-noise ratio and large, representative samples of individual galaxy detections, the AURORA emission-line diagrams presented here definitively confirm a physical picture in which chemically young, α -enhanced, massive stars photoionize the interstellar medium (ISM) in distant galaxies with a harder ionizing spectrum at fixed nebular metallicity than in their z ∼ 0 counterparts. We also uncover previously unseen evolution prior to z ∼ 2 in the [O iii ] λ 5007/H β versus [N ii ] λ 6583/H α diagram, which motivates deep NIRSpec observations at even higher redshift. Finally, we present the first statistical sample of rest-frame near-IR emission-line diagnostics in star-forming galaxies at high redshift. In order to truly interpret rest-frame near-IR line ratios including [Fe ii ] λ 1.257 μ m, we must obtain better constraints on dust depletion in the high-redshift ISM.

We present an analysis of the rest-frame optical (lambda similar or equal to 3100-5600 & Aring;) spectrum of a log(10)(M-*/M-circle dot) = 8.6 star-forming galaxy at z=8.271 (EXCELS-63107) from JWST/NIRSpec medium-resolution observations taken as part of the Early eXtragalactic Continuum and Emission Line Science (EXCELS) survey. The galaxy (EXCELS-63107) is compact, with a size consistent with local star-forming cluster complexes (r(e) < 200pc), and exhibits an extremely steep UV continuum slope measured from JWST/NIRCam photometry (beta =-3.3 +/- 0.3). The JWST/NIRSpec G395M spectrum of EXCELS-63107 is notable for its strong [OIII]lambda 4363 auroral-line emission relative to the [OIII]lambda 5007 forbidden line. Via a detailed emission-line and photoionization-modelling analysis, we find that the observed properties of EXCELS-63107 are consistent with the presence of an ionizing source with an effective temperature of T (eff) greater than or similar to 80 000 K heating ionized gas with a density of n(e) < 10(4) cm(-3) to a volume-averaged electron temperature of T-e similar or equal to 34 000 K. Crucially, we find that stellar population models assuming a standard initial mass function (IMF) are not capable of producing the required heating. We determine an oxygen abundance of 12+log(O/H)}= 6.89(-0.21)(+0.26) (similar or equal to 1.6 per cent of solar) which is one of the lowest directly constrained oxygen abundances measured in any galaxy to date, and similar or equal to 10 x lower than is typical for z similar or equal to 8 galaxies with the same stellar mass. The extremely low metallicity of EXCELS-63107 places it in a regime in which theoretical models expect a transition to a top-heavy IMF, and we speculate that a similar or equal to 10-30 xexcess of M > 50 M-circle dot stars is one plausible explanation for its observed properties. However, more exotic scenarios, such as Pop III star formation within a mildly enriched halo, are also consistent with the observations.

We present CAPERS-LRD-z9, a little red dot (LRD) which we confirm to be a z=9.288 broad-line AGN (BLAGN). First identified as a high-redshift LRD candidate from PRIMER NIRCam photometry, follow-up NIRSpec/PRISM spectroscopy of CAPERS-LRD-z9 from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS) has revealed a broad 3500 km s^-1 Hβ emission line and narrow [O III]λλ4959,5007 lines, indicative of a BLAGN. Based on the broad Hβ line, we compute a canonical black-hole mass of log(M_BH/M_⊙)=7.58±0.15, although full consideration of systematic uncertainties yields a conservative range of 6.655% (although systematic uncertainties on the black-hole mass prevent strong conclusions). However, the shape of the UV continuum differs from typical high-redshift star-forming galaxies, indicating that this UV emission may also be of AGN origin, and hence the true stellar mass of the host may be still lower.

Accurately quantifying the ionizing photon production efficiency (xi(ion)) of z greater than or similar to 6 star-forming galaxies (SFGs) is necessary to fully understand their contribution to reionization. In this study, we investigate the ionizing properties of N=279 SFGs selected at z similar or equal to 6.9-7.6 from two of the largest JWST Cycle-1 imaging programmes; PRIMER (Public Release IMaging for Extragalactic Research) and JWST Advanced Deep Extragalactic Survey (JADES). We use bagpipes to consistently infer the equivalent widths (W-lambda) of their [O iii] + H beta emission lines and their physical properties. To supplement this sample, we measure W lambda([O iii] + H beta) photometrically for N=253z(spec)=3.2-3.6 SFGs selected from the VANDELS spectroscopic survey. Comparing these samples, we find a strong apparent redshift evolution in their median W-lambda([O iii] + H beta), increasing from W-lambda([O iii] + H beta)=380 +/- 30 & Aring; in VANDELS to W-lambda([O iii] + H beta)=540 +/- 25 & Aring; in PRIMER+JADES. Concentrating on the JWST sample (z greater than or similar to 7), we find that W-lambda([O iii] + H beta) correlates with stellar mass and ultraviolet (UV) luminosity, with high-mass, MUV-faint galaxies producing systematically weaker emission lines. Moreover, we discover a departure from the standard lognormal shape of the W-lambda([O iii] + H beta) distribution, with a more pronounced tail towards lower W-lambda([O iii] + H beta), consistent with increasingly bursty star formation. Using W-lambda([O iii] + H beta) as a proxy for xi(ion), and UV spectral slope as a proxy for Lyman-continuum escape (f(esc)(LyC)), we uncover a minority of galaxies with high xi(ion) and f(esc)(LyC) (e.g. log(xi(ion)/erg(-1)Hz)similar or equal to 25.6 and f(esc)(LyC)similar or equal to 0.15). However, we find the ionizing photon budget at z greater than or similar to 7 is dominated by galaxies with more moderate output, close to the median values of log(xi(ion)/erg(-1)Hz)similar or equal to 25.3 and f(esc)(LyC)similar or equal to 0.05. Our results are consistent with estimates for the number of ionizing photons required to power reionization at z greater than or similar to 7, with no evidence for over or underproduction.

Context. One of the surprising early findings with JWST has been the discovery of a strong "roll-over" or a softening of the absorption edge of Ly alpha in a large number of galaxies at z greater than or similar to 6, in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as strong cumulative damped Ly alpha absorption (DLA) wings from high column densities of neutral atomic hydrogen (H I), signifying major gas accretion events in the formation of these galaxies. Aims. To explore this new phenomenon systematically, we assembled the JWST/NIRSpec PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 584 galaxies at z = 5.0 - 13.4, designed to study the physical properties and gas in and around galaxies during the reionization epoch. Methods. We characterized this benchmark sample in full and spectroscopically derived the galaxy redshifts, metallicities, star formation rates, and ultraviolet (UV) slopes. We defined a new diagnostic, the Ly alpha damping parameter D-Ly alpha, to measure and quantify the net effect of Ly alpha emission strength, the H I fraction in the intergalactic medium, or the local H I column density for each source. The JWST-PRIMAL survey is based on the spectroscopic DAWN JWST Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools. All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. Results. We find that the fraction of galaxies showing strong integrated DLAs with N-HI > 10(21) cm(-2) only increases slightly from approximate to 60% at z approximate to 6 up to approximate to 65 - 90% at z > 8. Similarly, the prevalence and prominence of Ly alpha emission is found to increase with decreasing redshift, in qualitative agreement with previous observational results. Strong Ly alpha emitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Conclusions. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine H I gas accretion. At z = 8 - 10, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed Ly alpha emission at z < 8.

We present a sample of 341 “little red dots” (LRDs) spanning the redshift range z ∼ 2–11 using data from the CEERS, PRIMER, JADES, UNCOVER, and NGDEEP surveys. Unlike past use of color indices to identify LRDs, we employ continuum slope fitting using shifting bandpasses to sample the same rest-frame emission blueward and redward of the Balmer break. This enables the detection of LRDs over a wider redshift range and with less contamination from galaxies with strong breaks that otherwise lack a rising red continuum. The redshift distribution of our sample increases at z < 8 and then undergoes a rapid decline at z ∼ 4.5, which may tie the emergence of these sources to the inside-out growth that galaxies experience during this epoch. We find that LRDs are ∼1 dex more numerous than X-ray- and UV-selected active galactic nuclei (AGN) at z ∼ 5–7. Within our sample, we have identified the first two X-ray-detected LRDs. An X-ray spectral analysis confirms that these AGN are moderately obscured with log ( N H / cm 2 ) of 23 . 3 − 1.3 + 0.4 and 22.7 2 − 0.16 + 0.13 . Our analysis reveals that reddened AGN emission dominates their rest-optical light, while the rest-UV originates from their host galaxies. We also present NIRSpec observations from the RUBIES survey of 17 LRDs that show broad emission lines consistent with AGN activity. The confirmed AGN fraction of our sample is 71% for sources with F444W < 26.5. In addition, we find three LRDs with blueshifted Balmer absorption features in their spectra, suggesting an outflow of high-density, low-ionization gas from near the central engine of these faint, red AGN.

We present a spectroscopic analysis of two star-forming galaxies at z similar or equal to 5 observed with JWST/NIRSpec as part of the Early eXtragalactic Continuum and Emission Line Science survey. The detection of the C III] lambda lambda 1906,09, [OII] lambda lambda 3726,29, [OIII] lambda lambda 4363,5007, and [N II] lambda 6584 emission lines enables an investigation of the C/O, N/O, and C/N abundance ratios using the temperature-sensitive method. The galaxies have stellar masses of log(M-star/M-circle dot)=8.09(-0.15)(+0.24 )and log(M-star/M-circle dot)=8.02-0.08+0.06 with metallicities of Z similar or equal to 0.2Z(circle dot) and Z similar or equal to 0.3Z circle dot. These metallicities are somewhat higher than is typical for other z greater than or similar to 5 galaxies with similar stellar mass and are comparable to z similar or equal to 0 analogues. Both galaxies display evidence for elevated N/O ratios with respect to the typical star-forming galaxies at z similar or equal to 0, with log(N/O)=-1.07(-0.13)(+0.17) and log(N/O)=-0.86(-0.11)(+0.15), respectively. In contrast, we find low C abundances, with log(C/O)=-0.82 +/- 0.22 and log(C/O)=-1.02 +/- 0.22, consistent with the predicted yields of core-collapse supernovae. Following the trend observed in other high-redshift sources, we find that the C/N ratios are lower at fixed O/H compared to the majority of local galaxies. Via a comparison to detailed chemical evolution models, we find that a standard or bottom-heavy initial mass function can explain the observed abundance ratios where the N-enrichment comes from intermediate-mass (similar or equal to 4-7M(circle dot)) stars. Our results demonstrate that robust measurements of CNO abundances with JWST can reveal unique enrichment pathways in galaxies as a function of both metallicity and redshift.

We present the properties of a massive, large, dusty, metal-rich, star-forming galaxy at z spec = 6.73. GOODSN-100182 was observed with JWST/NIRSpec as part of the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey, and is also covered by public multiwavelength Hubble Space Telescope and JWST imaging. While the large stellar mass of GOODSN-100182 (∼10 10 M ⊙ ) was indicated prior to JWST, NIRCam rest-frame optical imaging now reveals the presence of an extended disk ( r eff ∼ 1.5 kpc). In addition, the NIRSpec R ∼ 1000 spectrum of GOODSN-100182 includes the detection of a large suite of rest-frame optical nebular emission lines ranging in wavelength from [O ii ] λ 3727 up to [N ii ] λ 6583. The ratios of Balmer lines suggest significant dust attenuation ( E ( B − V ) gas = 0.4 0 − 0.09 + 0.10 ), consistent with the red rest-frame UV slope inferred for GOODSN-100182 ( β = −0.50 ± 0.09). The star formation rate based on dust-corrected H α emission is log ( SFR(H α ) / M ⊙ yr − 1 ) = 2.0 2 − 0.14 + 0.13 , well above the z ∼ 7 star-forming main sequence in terms of specific star formation rate. Strikingly, the ratio of [N ii ] λ 6583/H α emission suggests almost solar metallicity, as does the ratio ([O iii ] λ 5007/H β )/([N ii ] λ 6583/H α ) and the detection of the faint [Fe ii ] λ 4360 emission feature. Overall, the excitation and ionization properties of GOODSN-100182 more closely resemble those of typical star-forming galaxies at z ∼ 2–3 rather than z ∼ 7. Based on public spectroscopy of the GOODS-N field, we find that GOODSN-100182 resides within a significant galaxy overdensity, and is accompanied by a spectroscopically confirmed neighbor galaxy. GOODSN-100182 demonstrates the existence of mature, chemically enriched galaxies within the first billion years of cosmic time, whose properties must be explained by galaxy formation models.

We present an analysis of eight star-forming galaxies with [z]=4.0 from the JWST Early eXtragalactic Continuum and Emission Line Survey for which we obtain robust chemical abundance estimates for the alpha-elements O, Ne, and Ar. The alpha-elements are primarily produced via core-collapse supernovae (CCSNe) which should result in alpha-element abundance ratios that do not vary significantly across cosmic time. However, Type Ia supernovae (SNe Ia) models predict an excess production of Ar relative to O and Ne. The Ar/O abundance ratio can therefore be used as a tracer of the relative enrichment of CCSNe and SNe Ia in galaxies. Our sample significantly increases the number of sources with measurements of O/Ar at z>2, and we find that our sample exhibits subsolar Ar/O ratios on average, with Ar/O=0.65 +/- 0.10(Ar/O)(circle dot). In contrast, the average Ne/O abundance is fully consistent with the solar ratio, with Ne/O=1.07 +/- 0.12(Ne/O)(circle dot). Our results support a scenario in which Ar has not had time to build up in the interstellar medium of young high-redshift galaxies, which are dominated by CCSNe enrichment. We show that these abundance estimates are in good agreement with recent Milky Way chemical evolution models, and with Ar/O trends observed for planetary nebulae in the Andromeda galaxy. These results highlight the potential for using multiple element abundance ratios to constrain the chemical enrichment pathways of early galaxies with JWST.

In this Letter, we measure the rest-frame optical and near-infrared sizes of 10 quiescent candidates at 3 < z < 5, first reported by Carnall et al. We use James Webb Space Telescope Near-Infrared Camera F277W and F444W imaging obtained through the public CEERS Early Release Science program and imcascade , an astronomical fitting code that utilizes multi-Gaussian expansion, to carry out our size measurements. When compared to the extrapolation of rest-optical size–mass relations for quiescent galaxies at lower redshift, 8 out of 10 candidates in our sample (80%) are on average more compact by ∼40%. A total of 7 out of 10 candidates (70%) exhibit rest-frame infrared sizes ∼10% smaller than rest-frame optical sizes, indicative of negative color gradients. Two candidates (20%) have rest-frame infrared sizes ∼1.4× larger than rest-frame optical sizes; one of these candidates exhibits signs of ongoing or residual star formation, suggesting this galaxy may not be fully quenched. The remaining candidate is unresolved in both filters, which may indicate an active galactic nucleus. Strikingly, we observe three of the most massive galaxies in the sample (log( M ⋆ / M ⊙ ) = 10.74–10.95) are extremely compact, with effective radii ∼0.7 kpc. Our findings provide no indication that the size evolution relation flattens out, and may indicate that the size evolution of quiescent galaxies is steeper than previously anticipated beyond z > 3.

We present determinations of the gas-phase and stellar metallicities of a sample of 65 star-forming galaxies at z similar or equal to 3.5 using rest-frame far-ultraviolet (FUV) spectroscopy from the VANDELS survey in combination with follow-up rest-frame optical spectroscopy from VLT/KMOS and Keck/MOSFIRE. We infer gas-phase oxygen abundances (Z(g); tracing O/H) via strong optical nebular lines and stellar iron abundances (M-star; tracing Fe/H) from full spectral fitting to the FUV continuum. Our sample spans the stellar mass range 8.5 < log(M-star/M-circle dot) < 10.5 and shows clear evidence for both a stellar and gas-phase mass-metallicity relation (MZR). We find that our O and Fe abundance estimates both exhibit a similar mass-dependence, such that Fe/H proportional to M-star(0.30 +/- 0.11) and O/H proportional to M-star(0.32 +/- 0.09). At fixed M-star we find that, relative to their solar values, O abundances are systematically larger than Fe abundances (i.e. alpha-enhancement). We estimate an average enhancement of (O/Fe)=2.65 +/- 0.16x(O/Fe)(circle dot) which appears to be independent of M-star. We employ analytic chemical evolution models to place a constraint on the strength of galactic-level outflows via the mass-outflow factor (eta). We show that outflow efficiencies that scale as eta proportional to M-star(-0.32) can simultaneously explain the functional form of of the stellar and gas-phase MZR, as well as the degree of alpha-enhancement at fixed Fe/H. Our results add further evidence to support a picture in which alpha-enhanced abundance ratios are ubiquitous in high-redshift star-forming galaxies, as expected for young systems whose interstellar medium is primarily enriched by core-collapse supernovae.

JWST has revealed a large population of compact, red galaxies at z>4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 95 LRDs from the JWST PRIMER survey with complete photometric coverage from 1-18 μm using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario's implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low-mass components, hinting at inhomogeneous obscuration. The AGN-only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning ∼2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The black hole and stellar masses inferred from the hybrid model lead to highly overmassive black holes even exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN or galaxy dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.