Constraining the major contributors to the ionisation of the early universe is an ongoing endeavour of high-redshift galaxy research. We measure the ionising photon production efficiency and Lyman Continuum escape fraction for a sample of 230 intermediate redshift (1.35. This control sample allows us to verify the correlations between ionising and spectral/physical properties suggested by previous studies. We find no significant correlations between the ionising photon production efficiency (ξ_ion) with the UV slope, M_UV, M_* or sSFR. We do find that ξ_ion correlates with [OIII]5007Å equivalent width (EW) (Spearman coefficient ρ =0.24; p< 4×10^-4) and Hα EW (ρ =0.63; p<< 1×10^-6) hold even at low EW albeit with more scatter. We also find that our novel approach to determining the ionising photon escape fraction f_esc results in values within theoretical ranges (0-10%) though vary substantially in comparison to the empirical results (median f_esc = 0.9%^+1.1_-0.5 including non-detections, median f_esc = 1.9%^+8.9_-1.8 above a 0.01% threshold). We find that this escape fraction method has consistently significant correlations with the redshift, SFR and M_UV and sample-dependent correlations with [OIII]5007Å EW,Hα EW and stellar mass.

We present a systematic investigation of the evolution of the mass-metallicity relation (MZR) and fundamental metallicity relation (FMR) using uniform metallicity diagnostics across redshifts z similar to 0 to z similar to 3.3. We present new Keck/Deep Imaging Multi-Object Spectrograph measurements of the [O II]lambda lambda 3726, 3729 emission line doublet for star-forming galaxies at z similar to 1.5 with existing measurements of redder rest-optical lines from the MOSFIRE Deep Evolution Field survey. These new observations enable uniform estimation of the gas-phase oxygen abundance using ratios of the [O II], H beta, and [O III] lines for mass-binned samples of star-forming galaxies in six redshift bins, employing strong line calibrations that account for the distinct interstellar medium ionization conditions at z < 1 and z > 1. We find that the low-mass power-law slope of the MZR remains constant over this redshift range with a value of gamma = 0.28 +/- 0.01, implying the outflow metal loading factor ( zeta(out)=Z(out)/ Z(ISM) M(out )Z(ISM)/ SFR ) scales approximately as zeta out proportional to M-*(-0.3) out to at least z similar to 3.3. The normalization of the MZR at 10(10) M-circle dot decreases with increasing redshift at a rate of dlog(O/H)/dz=-0.11 +/- 0.01 across the full redshift range. We find that any evolution of the FMR is smaller than 0.1 dex out to z similar to 3.3. We compare to cosmological galaxy formation simulations, and find that IllustrisTNG matches our measured combination of a nearly-invariant MZR slope, rate of MZR normalization decrease, and constant or very weakly evolving FMR. This work provides the most detailed view of MZR and FMR evolution from the present day through Cosmic Noon with a fine time sampling of 1-3 Gyr, setting a robust baseline for metallicity evolution studies at z > 4 with JWST.

We present the nebular attenuation curves and dust covering fractions for 24 redshift z=1.5-4.4 star-forming galaxies using multiple Balmer and Paschen lines from the JWST/AURORA survey. Nebular reddening derived from Paschen lines exceeds that from Balmer lines for at least half the galaxies in the sample when assuming the commonly-adopted Galactic extinction curve, implying the presence of optically-thick star formation. The nebular attenuation curves exhibit a broad range of normalizations (Rv ~ 3.2-16.4). Motivated by the offsets in reddening deduced from the Balmer and Paschen lines, and the high Rv values for the individual nebular attenuation curves, both of which suggest variations in the dust-stars geometry, we propose a model with a subunity dust covering fraction (fcov). Fitting such a model to the HI recombination line ratios indicates fcov ~ 0.6-1.0. The normalizations of the nebular attenuation curves, Rv, are driven primarily by fcov and the mix of optically-thick and thin OB associations. Thus, the diversity of nebular attenuation curves can be accommodated by assuming dust grain properties similar to that of Milky Way sightlines but with a subunity covering fraction of dust. Integrated measurements of multiple Balmer and Paschen lines can be used to place novel constraints on the dust covering fraction towards OB associations. These, in turn, provide new avenues for exploring the role of dust and gas covering fraction in a number of relevant aspects of high-redshift galaxies, including the impact of stellar feedback on ISM porosity and the escape of Ly-alpha and Lyman continuum radiation.

We present detections of auroral emission lines of [O iii], [O ii], [S iii], and [S ii] in deep JWST/NIRSpec spectroscopy for 41 star-forming galaxies at z = 1.4-7.2 from the AURORA survey. We combine these new observations with 98 star-forming galaxies at z = 1.3-10.6 with detected auroral lines drawn from the literature to form a sample of 139 high-redshift galaxies with robust electron temperature and direct-method oxygen abundance determinations. This sample notably covers a wider dynamic range in metallicity than previous work, spanning 0.02-0.9 Z circle dot. We calibrate empirical relations between 19 emission-line ratios and oxygen abundance, providing a robust tool set to infer accurate gas-phase metallicities of high-redshift galaxies when auroral lines are not detected. While calibrations based on lines of alpha elements (O, Ne, S, Ar) appear reliable, we find significant scatter in calibrations involving lines of N driven by a high dispersion in N/O at fixed O/H, suggesting that N-based line ratios are less reliable tracers of the oxygen abundance at high redshift. These new high-redshift calibrations are notably offset from those based on typical z similar to 0 galaxy and H ii region samples, and are better matched by samples of extreme local galaxies that are analogs of high-redshift sources. The new metallicity calibrations presented in this work pave the way for robust studies of galaxy chemical evolution in the early Universe, leading to a better understanding of baryon cycling and galaxy formation from Cosmic Noon through the Epoch of Reionization.

We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at z >= 10 with James Webb Space Telescope (JWST)/NIRSpec prism observations. We compare the properties of strong ultraviolet (UV) line emitters, traced by intense C IV emission, with those of more 'typical' sources with weak or undetected C IV . The more typical (or 'C iv-weak') sources reveal significant scatter in their C III] line strengths, UV continuum slopes, and physical sizes, spanning C III] equivalent widths (EWs) of similar to 1-51 angstrom, UV slopes of beta similar to -1.6 to-2.6, and half-light radii of similar to 50-1000 pc. In contrast, C IV -strong sources occupy the tail of these distributions, with C III] EWs of 16-51 angstrom, UV slopes beta less than or similar to -2.5, compact morphologies (r(50) less than or similar to 100 pc), and elevated star formation surface densities (Sigma(SFR) greater than or similar to 100 M-circle dot yr(-1) kpc(-2)). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short time-scales (<= 3 Myr), with strong C iv emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong C IV and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that active galactic nuclei are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionization models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr.

The multi-cycle JWST Treasury program NEXUS will obtain cadenced imaging and spectroscopic observations around the North Ecliptic Pole during 2024-2028. Here we report a systematic search for nuclear variability among ∼ 25k sources covered by NIRCam (F200W+F444W) imaging using the first two NEXUS epochs separated by 9 months in the observed frame. Difference imaging techniques reach 1σ variability sensitivity of 0.18 mag (F200W) and 0.15 mag (F444W) at 28th magnitude (within 0".2 diameter aperture), improved to 0.01 mag and 0.02 mag at <25th magnitude, demonstrating the superb performance of NIRCam photometry. The difference imaging results represent significant improvement over aperture photometry on individual epochs (by >30%). We identify 465 high-confidence variable sources among the parent sample, with 2-epoch flux difference at >3σ from the fiducial variability sensitivity. Essentially all these variable sources are of extragalactic origin based on preliminary photometric classifications, and follow a similar photometric redshift distribution as the parent sample up to z_ phot>10. While the majority of these variability candidates are likely normal unobscured AGNs, some of them may be rare nuclear stellar transients and tidal disruption events that await confirmation with spectroscopy and continued photometric monitoring. We also constrain the photometric variability of ten spectroscopically confirmed broad-line Little Red Dots (LRDs) at 3≲ z ≲ 7, and find none of them show detectable variability in either band. We derive stringent 3σ upper limits on the F444W variability of ∼ 3-10% for these LRDs, with a median value of ∼ 5%. These constraints imply weak variability in the rest-frame optical continuum of LRDs.

We present a spectroscopic sample of 24 broad-line AGNs (BLAGNs) at 3 less than or similar to z less than or similar to 6 selected using F322W2+F444W NIRCam/WFSS grism spectroscopy of the central 100 arcmin2 area of the NEXUS survey. Among these BLAGNs, 15 are classified as Little Red Dots (LRDs) based on their rest-frame UV-optical spectral slopes and compact morphology. The number density of LRDs is similar to 10-5 cMpc-3, with a hint of declining towards lower redshift. These BLAGNs span broad H alpha luminosities of similar to 1042.2-1043.5 erg s-1, black hole masses of similar to 106.3-108.4 M circle dot, and Eddington ratios of similar to 0.1-1, though the estimates of black hole mass and Eddington ratio carry large systematic uncertainties. Half of the LRDs show strong Balmer absorption, suggesting high-density gas surrounding the line-emitting region. We detect extended (hundreds of parsecs) rest-frame UV-optical emission from the host galaxy in the majority of these LRDs, which contributes significantly or even dominantly to their total UV emission and largely accounts for the peculiar UV upturn of their spectral energy distribution. We also measure the small-scale (less than or similar to 1 cMpc) clustering of these BLAGNs and LRDs by cross-correlating with a photometric galaxy sample. Extrapolating the power-law two-point correlation function model to large linear scales, we infer a linear bias of 3.69-2.21+2.78 and typical halo masses of a few & times;1011h-1 M circle dot for BLAGNs at the sample median redshift of z similar to 4.5. However, the inferred linear bias and halo masses of LRDs, while formally consistent with those for BLAGNs at similar to 1.5 sigma, appear too large to be compatible with their space density, suggesting LRDs may have strong excess clustering on small scales.

We present the first robust helium (He) abundance measurements in star-forming galaxies at redshifts 1.6 ≲ z ≲ 3.3 using deep, moderate-resolution JWST/NIRSpec spectroscopy from the AURORA survey. We establish a high- z He sample consisting of 20 galaxies with multiple high-signal-to-noise-ratio (>5 σ ) He i emission-line detections, including the critical near-infrared λ 10833 line. This is the first study at high redshift leveraging λ 10833 to break degeneracies between temperature, electron density, optical depth, and He ^+ /H ^+ , enabling reliable He abundance determinations in the early Universe. We use a custom Markov Chain Monte Carlo framework incorporating direct-method electron temperature priors, extended optical depth ( τ _λ _3890 ) model grids up to densities of 10 ^6 cm ^−3 , and simultaneous fits of the physical conditions and He i /H i line ratios to derive ionic He ^+ /H ^+ abundances. Most of the AURORA galaxies follow the extrapolated z ∼ 0 He/H–O/H trend, indicating modest He enrichment by z ∼ 2–3. However, we identify a subpopulation of four galaxies that exhibit elevated He mass fractions (Δ Y > 0.03) without corresponding enhancements in N/O or α -elements (∼20% of the sample). This abundance pattern is inconsistent with enrichment from asymptotic giant branch stars, but favors early He enrichment from very massive stars ( M ≳ 100 M _⊙ ), which can eject He-rich, N-poor material via stellar winds and binary stripping in young stellar populations. We speculate that these elevated-He systems may represent an early phase of globular cluster (GC) formation where N enrichment is still lagging behind He production. This work demonstrates the power of JWST multi-line He i spectroscopy for tracing early stellar feedback, enrichment pathways, and GC progenitor signatures in the high-redshift Universe.

We present ionizing photon production efficiencies ( ξ _ion ) for 63 z = 1.5–6.9 star-forming galaxies using precise nebular dust attenuation corrections from the JWST Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey. A subset of objects within AURORA have individually determined nebular dust attenuation curves, which vary significantly in shape and normalization, resulting in reduced systematic uncertainty when constraining the total attenuation of H α luminosity, and thus the intrinsic ionizing output within our sample. We find evidence for positive correlations between ξ _ion and redshift, equivalent width of [O iii ] λ 5007, and O32 = [O iii ] λ 5007/[O ii ] λλ 3726, 3729, and negative correlations between ξ _ion and stellar attenuation, UV luminosity ( L _UV ), stellar mass, and direct-method metallicity. We test alternate dust prescriptions within this sample, and find that the total attenuation is lower when using the commonly assumed Galactic extinction curve or when assuming that stellar attenuation is equal to nebular attenuation. We also find that assuming either of these alternate dust prescriptions can change the slope of the relationships between ξ _ion and galaxy property, notably inducing a flat trend between ξ _ion and L _UV within AURORA. While the novel nebular dust curves derived from AURORA spectroscopy reveal obscured ionizing photon production within star-forming galaxies at these redshifts, a more complete understanding of stellar attenuation is required to fully reduce the dust systematics on ξ _ion for inclusion in reionization models.

We present argon abundances from a sample of 46 star-forming galaxies at z = 2-3.5 from the Assembly of Ultradeep Rest-Optical Observations Revealing Astrophysics (AURORA) program. Although argon is an alpha-element produced by core collapse supernovae (CCSNe), the latest supernova yield models suggest additional argon production and enrichment by Type Ia supernovae (SNe Ia), unlike other alpha-elements such as oxygen. To study the relationship between argon and oxygen abundances, we construct two median-stacked composite spectra for separate z = 2.0-2.6 and z = 2.8-3.5 redshift bins, presenting more representative measurements than previous samples that require individual detection of faint lines. Abundance ratios were determined using an empirical calibration based on the strength of the [ArIII]lambda 7137 emission line relative to the [O III]lambda 5008 emission line. With this calibration, we estimate argon abundances (Ar/O) of 0.42-0.10+0.12(Ar/O)circle dot for the < z > = 2.26 bin and 0.42-0.11+0.12(Ar/O)circle dot for the < z > = 3.15 bin, suggesting minimal SNe Ia and dominant CCSNe enrichment in this sample. Comparison of our abundance measurements of z similar to 2-3 AURORA galaxies with chemical evolution modeling of Milky Way stars shows consistency with the Milky Way bulge component, suggesting a rapid star formation timescale. However, even larger samples of actively star-forming galaxies with available argon abundances, as well as comparisons between argon abundance and other critical galaxy properties (e.g., specific star formation rate, sSFR) and models (e.g., one tuned specifically to this redshift range) are needed to draw stronger conclusions on the role of argon in galactic chemical enrichment at cosmic noon.

We present Keck/MOSFIRE H-band spectroscopic measurements covering the [CIII]1907, CIII]1909 doublet for a sample of 8 z 7 spectroscopically-confirmed star-forming galaxies drawn from the Reionization Era Bright Emission Line Survey (REBELS). This sample is notable for its bright median UV luminosity (Muv=-22.5 AB) and large median stellar mass (log(Mstar/Msun)=9.2). Although three sources show tentative evidence of a CIII] detection, we obtain no confident detections for any of the 8 REBELS sources. The median [CIII]1907+CIII]1909 3-sigma upper limit in equivalent width (EW) for the REBELS-MOSFIRE sample is 6.5 AA, and a stack of their H-band MOSFIRE spectra yields a non-detection with an associated 3-sigma upper limit of 2.6 AA. These upper limits fall significantly below the CIII] EW measured in a composite spectrum of representative z 7 star-forming galaxies, as well as those measured for notable early star-forming galaxies such as GN-z11, GHZ2, GS-z12, and RXCJ2248-ID. The lack of strong CIII] emission can be understood within the context of the stellar populations of the REBELS galaxies, as well as the ionization conditions and gas-phase metallicity implied by rest-frame optical spectroscopic properties ([OIII]+Hb EWs, and [OIII]5007/[OII]3727 and [NeIII]3869/[OII]3727 line ratios). The REBELS-MOSFIRE sample represents the higher-mass, higher-metallicity, lower-excitation tail of the z 7 galaxy population, whose ionizing properties must be fully characterized to constrain the role of star-forming galaxies during cosmic reionization.

We select a mass-complete sample of 225 quiescent galaxies at z > 2 with M-& lowast; > 10(10 )M(circle star) from PRIMER and JADES photometry spanning a total area of similar or equal to 320 sq. arcmin. Our analysis is restricted to only area with optical coverage in three Hubble Space Telescope ( HST ) ACS filters, which we show is important for selecting the most complete and clean samples. We investigate the contamination in our sample via James Webb Space Telescope (JWST) NIRSpec spectroscopy, Chandra X-ray imaging, and ALMA interferometry, calculating a modest contamination fraction of 12 . 9(-3.1)(+4.0) per cent. The removal of HST data increases star-forming galaxy contamination by similar or equal to 10 per cent and results in a similar or equal to 20 per cent loss of candidates recovered from HST + JWST data combined. We calculate massive quiescent galaxy number densities at 2 < z < 5, finding values three times larger than pre-JWST estimates, but generally in agreement with more-recent and larger-area JWST studies. In comparison with simulations, we find that most can now reproduce the observed number density at 2 < z < 3; however, they still increasingly fall short at z > 3, up to similar or equal to 1 dex. We place 14 of our z > 3 massive quiescent galaxies on the BPT and WHaN diagrams using medium-resolution spectroscopic data from the EXCELS survey, finding a very high incidence of weak active galactic nucleus ( similar or equal to 50 per cent), consistent with recent results at cosmic noon. This is interesting in the context of 'maintenance-mode' feedback, which is invoked in many simulations to prevent the re-ignition of quenched galaxies. To properly characterize the evolution of early massive quiescent galaxies, greater coverage in optical filters and significantly larger spectroscopic samples will be required.

We study 24 massive quiescent galaxies with logM(*)/M-circle dot>10 at 1 < z < 3 with JWST/NIRSpec medium-resolution observations from the Early Extragalactic Continuum and Emission Line Survey (EXCELS). We reconstruct their star formation histories and find that they have large bursts (100-1000 M-circle dot yr(-1)), followed by a rapid truncation of star formation. The number densities of the quenched galaxies in our sample that we predict underwent a submillimeter phase are consistent with submillimeter galaxies being the progenitors of our quenched population. The median post-starburst visibility time is similar to 600 Myr, with more massive galaxies ( logM(*)/M-circle dot>10.7 ) exhibiting shorter visibility times than lower-mass galaxies. The range of quenching times-defined as the time from the peak starburst to the time of quiescence-found in this sample (0.06-1.75 Gyr) suggests multiple quenching pathways, consistent with previous studies. We do not see evidence for quenching mechanisms varying with redshift between 1 < z < 3. We detect evidence for weak active galactic nucleus activity in four out of the eight galaxies with robust emission line detections, based on line ratio diagnostics. Our findings suggest that there is a diverse range of quenching mechanisms at Cosmic Noon, and support a scenario in which the primary quenching mechanisms are rapid (<500 Myr) following a starburst.

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.

We present an analysis of deep JWST/NIRSpec spectra of star-forming galaxies at z similar or equal to 1.4-10, observed as part of the Assembly of Ultra-deep Rest-optical Observations Revealing Astrophysics (AURORA) survey. We infer median low-ionization electron densities of 268(-49)(+45) cm(-3), 350(-76)(+140) cm(-3), and 480(-310)(390) cm(-3) at redshifts z = 2 . 3, z = 3 . 2, and z = 5 . 3, respectively, which is best described by an evolutionary trend following (1 + z)1.5 +/- 0.6 . We identify weak positive correlations between electron density and star formation rate (SFR) as well as SFR surface density, but no significant trends with stellar mass or specific SFR. Correlations with rest-optical emission line ratios show densities increasing with [NeIII]A3869 /[OII]A3727 and, potentially, [OIII]A5007/[OII]A3727, although variations in dust attenuation complicate the latter. Additionally, electron density is more strongly correlated with distance from the local Baldwin, Phillips, and Terlevich (BPT) sequence than can be explained by simple photoionization models. We further derive electron densities from the [C III ] doublet probing higher ionization gas, and find a median value of 1.4(-0.5)(+0.7) x 10(4) cm(-3), '30 times higher than densities inferred from [S II ]. This comparison suggests a consistent HII region structure across cosmic time with dense, high-ionization interiors surrounded by less dense, low-ionization gas. We compare measurements of AURORA galaxies to predictions from the SPHINX galaxy formations, highlighting the interplay between residual molecular cloud pressure in young galaxies and feedback from stellar winds and supernovae as galaxies mature.

We analyze JWST spectroscopic and HST+JWST photometric observations of 659 star-forming galaxies at 1.4 < z < 9 from DR3 of the JADES survey and the AURORA Cycle 1 program. We measure the star-forming main sequence (SFMS) for galaxies above 10^8.5 M_⊙ where the sample is largely representative, estimating star-formation rates (SFRs) using the Hα line flux and rest-frame far UV (1600Å) continuum measurements, each independently corrected for dust attenuation. We find that the intrinsic, measurement-error-subtracted scatter in the SFMS (σ_ int) increases with decreasing stellar mass for the Hα-based SFMS, and we find no mass dependence of σ_ int in the UV-based SFMS. Additionally, we find that σ_ int decreases with increasing redshift, from 0.36^+0.02_-0.02 dex to 0.22^+0.08_-0.07 dex (Hα SFMS), and from 0.28^+0.02_-0.02 dex to 0.20^+0.08_-0.07 dex (UV SFMS) between z∼2 and z∼ 6.5. We also measure the redshift evolution of the specific SFR and find that, assuming sSFR∝ (1+z)^γ, γ=1.89^+0.16_-0.15 for the Hα-based SFMS, and γ=1.36^+0.13_-0.13 for the UV-based SFMS. Analyzing the observed Hα/UV luminosity ratios and star-formation histories from the prospector fitting code, we find that 41–60% of the sample is inconsistent with having a constant star-formation history. Finally, we find tentative evidence for shorter SFR burst timescales with increasing redshift based on the distribution of L_Hα/νL_ν,1600 vs. Δlog(L_Hα). Taken together, these results are consistent with theoretical predictions of bursty star formation in the early Universe and provide valuable constraints for theoretical models of galaxy evolution.

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

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.

Integral field spectroscopy (IFS) is a powerful tool for understanding the formation of galaxies across cosmic history. We present the observing strategy and first results of MSA-3D, a novel JWST program using multi-object spectroscopy in a slit-stepping strategy to produce IFS data cubes. The program observed 43 normal star-forming galaxies at redshifts 0.5 ≲ z ≲ 1.5, corresponding to the epoch when spiral thin-disk galaxies of the modern Hubble sequence are thought to emerge, obtaining kiloparsec-scale maps of rest-frame optical nebular emission lines with spectral resolution R ≃ 2700. Here we describe the multiplexed slit-stepping method, which is >15 times more efficient than the NIRSpec IFS mode for our program. As an example of the data quality, we present a case study of an individual galaxy at z = 1.104 (stellar mass M * = 10 10.3 M ⊙ , star formation rate, SFR = 3 M ⊙ yr −1 ) with prominent face-on spiral structure. We show that the galaxy exhibits a rotationally supported disk with moderate velocity dispersion ( σ = 3 6 − 4 + 5 km s −1 ), a negative radial metallicity gradient (−0.020 ± 0.002 dex kpc −1 ), a dust attenuation gradient, and an exponentially decreasing SFR density profile that closely matches the stellar continuum. These properties are characteristic of local spirals, indicating that mature galaxies are in place at z ∼ 1. We also describe the customized data reduction and original cube-building software pipelines that we have developed to exploit the powerful slit-stepping technique. Our results demonstrate the ability of JWST slit-stepping to study galaxy populations at intermediate to high redshifts, with data quality similar to current surveys of the z ∼ 0.1 Universe.

We report the detection of a 13$\sigma$ H$\alpha$ emission line from HDF850.1 at $z=5.188\pm0.001$ using the FRESCO NIRCam F444W grism observations. Detection of H$\alpha$ in HDF850.1 is noteworthy, given its high far-IR luminosity, substantial dust obscuration, and the historical challenges in deriving its redshift. HDF850.1 shows a clear detection in the F444W imaging data, distributed between a northern and southern component, mirroring that seen in [CII] from the Plateau de Bure Interferometer. Modeling the SED of each component separately, we find that the northern component has a higher mass, star formation rate (SFR), and dust extinction than the southern component. The observed H$\alpha$ emission appears to arise entirely from the less-obscured southern component and shows a similar $\Delta$v$\sim$+130 km/s velocity offset to that seen for [CII] relative to the source systemic redshift. Leveraging H$\alpha$-derived redshifts from FRESCO observations, we find that HDF850.1 is forming in one of the richest environments identified to date at $z>5$, with 100 $z=5.17-5.20$ galaxies distributed across 10 structures and a $\sim$(15 cMpc)$^3$ volume. Based on the evolution of analogous structures in cosmological simulations, the $z=5.17-5.20$ structures seem likely to collapse into a single $>$10$^{14}$ $M_{\odot}$ cluster by $z\sim0$. Comparing galaxy properties forming within this overdensity with those outside, we find the masses, SFRs, and $UV$ luminosities inside the overdensity to be clearly higher. The prominence of H$\alpha$ line emission from HDF850.1 and other known highly-obscured $z>5$ galaxies illustrates the potential of NIRCam-grism programs to map both the early build-up of IR-luminous galaxies and overdense structures.