Showing 1–50 of 284 results for author: Shapley, A

OutThere Survey: Addressing $\mathrm{ξ_{ion}}$ and $\mathrm{f_{esc}}$ with a population of average galaxies at z$\sim$2

Authors: Ravi Jaiswar, Anshu Gupta, Elisabete da Cunha, Cathryn M. Trott, Andrew Battisti, Isabel Perez, Karl Glazebrook, Lalitwadee Kawinwanichakij, Zackary L. Hutchens, Ivelina Momcheva, Claudia Del. P Lagos, Themiya Nanayakkara, Colin Jacobs, Danilo Marchesini, David A. Wake, Alice Shapley, Gabriel Brammer, Raphael Hviding, Casey Papovich, Ryan L. Sanders, Rhea-Silvia Remus, Mengtao Tang, Daniel Stark, Vincente Estrada-Carpenter, Joshua Speagle , et al. (2 additional authors not shown)

Abstract: 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 ($1.3<z<2.6$) sources observed as a part of the \textit{OutThere survey}; a pure-parallel, wide-area JWST/NIRISS survey with accompanyi… ▽ More 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 ($1.3<z<2.6$) sources observed as a part of the \textit{OutThere survey}; a pure-parallel, wide-area JWST/NIRISS survey with accompanying JWST/NIRCam, NIRISS and HST photometry. The low threshold emission selection criteria for this sample makes for a large and robust control, against which other works may be contrasted, particularly for low-mass galaxies above z$>$5. This control sample allows us to verify the correlations between ionising and spectral/physical properties suggested by previous studies. We find no significant correlations between the ionising photon production efficiency ($\mathrm{ξ_{ion}}$) with the UV slope, $\mathrm{M_{UV}}$, M$_*$ or sSFR. We do find that $\mathrm{ξ_{ion}}$ correlates with [OIII]5007Å\, equivalent width (EW) (Spearman coefficient $ρ$ =0.24; p$< 4\times10^{-4}$) and H$α$ EW ($ρ$ =0.63; p$<< 1\times10^{-6}$) hold even at low EW albeit with more scatter. We also find that our novel approach to determining the ionising photon escape fraction $\mathrm{f_{esc}}$ results in values within theoretical ranges (0-10\%) though vary substantially in comparison to the empirical results (median $\mathrm{f_{esc}} = 0.9\%^{+1.1}_{-0.5}$ including non-detections, median $\mathrm{f_{esc}} = 1.9\%^{+8.9}_{-1.8}$ 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,H$α$ EW and stellar mass. △ Less

Submitted 20 August, 2026; originally announced August 2026.

Comments: 20 pages, 13 figures, 5 tables

Quasar Impostors: Two Extremely UV-Bright ($M_{\rm UV}\approx-23.5$) Reionisation-Epoch Galaxies Powered by Very Massive Stars

Authors: Daming Yang, Joseph F. Hennawi, Sarah E. I. Bosman, Frederick B. Davies, Rychard Bouwens, Timo Kist, Eduardo Bañados, Jiamu Huang, Alice E. Shapley, Marianne Vestergaard, Hiddo S. B. Algera, Silvia Belladitta, Anna-Christina Eilers, Xiaohui Fan, Francesco Guarneri, Xiangyu Jin, Romain A. Meyer, Elia Pizzati, Huub Röttgering, Jan-Torge Schindler, Mauro Stefanon, Feige Wang, Jinyi Yang

Abstract: The extreme bright end of the galaxy UV luminosity function during reionisation remains poorly constrained, particularly where the galaxy and quasar luminosity functions overlap and source classification becomes ambiguous. We present JWST/NIRSpec and ALMA Band-6 observations of J1450-0144 ($z=6.627$) and J1429-0104 ($z=6.796$), two $M_{\rm UV}\simeq-23.5$ sources originally classified as faint qua… ▽ More The extreme bright end of the galaxy UV luminosity function during reionisation remains poorly constrained, particularly where the galaxy and quasar luminosity functions overlap and source classification becomes ambiguous. We present JWST/NIRSpec and ALMA Band-6 observations of J1450-0144 ($z=6.627$) and J1429-0104 ($z=6.796$), two $M_{\rm UV}\simeq-23.5$ sources originally classified as faint quasars by SHELLQs. NIRSpec reveals blue UV continua, strong P Cygni profiles in N V, Si IV, and C IV, broad He II $\lambda1640$ emission with rest-frame equivalent widths of $8.8\pm1.2$ and $3.7\pm1.1$ Å, respectively, and narrow nebular lines, reclassifying both as extremely UV-luminous galaxies. Standard population-synthesis models cannot simultaneously reproduce the strong He II and wind features, whereas models incorporating very massive stars (VMS; $M\gtrsim100\,M_\odot$) with dedicated wind prescriptions can. These models favor a star-formation duration of 2-4 Myr for J1450-0144, with a broader allowed range for J1429-0104, stellar masses of $\log(M_\star/M_\odot)\approx9.2$-$9.9$, and star-formation rates of $\simeq300$-$540\,M_\odot\,{\rm yr}^{-1}$. Under the same VMS wind models, equivalent-width diagnostics imply $M_{\rm up}\gtrsim225\,M_\odot$ for J1429-0104, while J1450-0144 lies beyond even the $M_{\rm up}=475\,M_\odot$ grid. ALMA detects luminous [C II] 158 $μ$m emission in both systems, with $L_{\rm [CII]}\approx0.8$ and $4.1\times10^{9}\,L_\odot$, respectively. J1429-0104 additionally shows bright dust continuum, with both [C II] and dust offset by $\sim5.4$ kpc from its UV emission. These sources demonstrate that VMS can power some of the most UV-luminous galaxies at cosmic dawn and show that source classifications, and hence the inferred demographics of both galaxies and quasars in the crossover regime, need revisiting. △ Less

Submitted 18 August, 2026; originally announced August 2026.

Comments: 18 figures, 4 tables. Submitted

Unprecedented Constraints on Gas Flows at High Redshift Using Deep JWST/NIRSpec Observations from the LyC22, EXCELS, and AURORA Surveys

Authors: Emily Kehoe, Alice E. Shapley, Adam C. Carnall, Fergus Cullen, Thomas M. Stanton, Daniel Schaerer, Rui Marques-Chaves, Charles C. Steidel, Ryan L. Sanders, Natalie Lam, Karla Z. Arellano-Cordova, Ryan Begley, Sophia R. Flury, Natalia G. Guseva, Timothy Heckman, Alaina Henry, Akio K. Inoue, Yuri I. Izotov, Ho-Hin Leung, Derek J. McLeod, Kate Rowlands, Alberto Saldana-Lopez, Dirk Scholte, Maya Skarbinski, Struan D. Stevenson , et al. (3 additional authors not shown)

Abstract: We investigate how low-ionization gas flows in typical star-forming galaxies at $z\sim3$ depend on galaxy intrinsic properties and viewing angle. For this analysis we use JWST/NIRSpec observations of rest-frame near-UV Fe II and Mg II absorption, and rest-frame optical Na D absorption. This study combines galaxies from the LyC22, EXCELS, and AURORA surveys and contains 176, 197, and 315 galaxies,… ▽ More We investigate how low-ionization gas flows in typical star-forming galaxies at $z\sim3$ depend on galaxy intrinsic properties and viewing angle. For this analysis we use JWST/NIRSpec observations of rest-frame near-UV Fe II and Mg II absorption, and rest-frame optical Na D absorption. This study combines galaxies from the LyC22, EXCELS, and AURORA surveys and contains 176, 197, and 315 galaxies, respectively, with Fe II, Mg II, and Na D coverage. Based on both individual and composite spectra, we find no statistically significant correlations between outflow velocity and galaxy properties. However, galaxies with detected outflows tend towards higher stellar masses, SFR, and $Σ_{\rm SFR}$ than those without outflows, suggesting that the two samples are not drawn from the same parent population. Finally, we additionally find that Mg II emission is preferentially detected in galaxies with lower stellar mass and $A_V$, and higher sSFR, consistent with conditions that favor the escape of resonantly scattered line and ionizing continuum radiation. We present the first evidence in $z\sim3$ star-forming galaxies that properties of the absorption lines depend on galaxy inclination, with more face-on systems showing stronger absorption and higher outflow velocities, while inflowing gas is more frequently detected in more highly inclined galaxies. These trends are consistent with observations at $z\lesssim1$ and predictions from cosmological simulations in which galactic winds are launched perpendicular to the galactic disks, while accretion occurs primarily along the disk plane. △ Less

Submitted 10 June, 2026; originally announced June 2026.

Comments: 31 pages, 14 figures, 3 tables, submitted to ApJ

The JADES Mass-Metallicity and Fundamental Metallicity Relations at $z\gtrsim2$ Using New High-Redshift Metallicity Calibrations

Authors: Natalie Lam, Leonardo Clarke, Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Gabriel B. Brammer, Naveen A. Reddy, Shreya Karthikeyan

Abstract: We present measurements of the mass-metallicity relation (MZR) and fundamental metallicity relation (FMR) at $1.4<z<7.0$ using stacked JWST/NIRSpec spectra of 601 star-forming galaxies from the JWST Advanced Deep Extragalactic Survey (JADES). Using the most up-to-date strong-line metallicity calibrations based on high-redshift galaxies, we derive gas-phase metallicities from composite spectra binn… ▽ More We present measurements of the mass-metallicity relation (MZR) and fundamental metallicity relation (FMR) at $1.4<z<7.0$ using stacked JWST/NIRSpec spectra of 601 star-forming galaxies from the JWST Advanced Deep Extragalactic Survey (JADES). Using the most up-to-date strong-line metallicity calibrations based on high-redshift galaxies, we derive gas-phase metallicities from composite spectra binned by stellar mass, redshift, and star-forming main sequence (SFMS) offset. We find that the MZR slope evolves weakly from $z\sim0$ out to $z\sim5$, with $γ\sim0.21\pm0.03$, while the normalization decreases smoothly with redshift at a rate of $d\log(\mathrm{O/H})/dz\sim-0.1$ out to $z\sim4$. Beyond $z\gtrsim5$, the low-mass end continues to decline in metallicity while the high-mass end remains broadly consistent with lower-redshift relations, producing a steeper overall MZR. We additionally find evidence for a shallow anti-correlation between deviations from the MZR and SFMS at fixed stellar mass at $z\sim1.4-5$. This anti-correlation, albeit with weaker SFR coupling than observed locally, suggests that an FMR is already beginning to emerge by $z\sim5$. Comparisons with recent observations and cosmological simulations show broad agreement, though no single simulation simultaneously reproduces the observed slopes and normalizations across all redshifts. Our results support a picture in which bursty star formation and strong stellar feedback increasingly shape the regulation of galaxy growth at high redshift, while also highlighting the need for substantially larger spectroscopic samples to robustly constrain the evolution of galaxy scaling relations at high-redshift. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Comments: 24 pages, 10 figures, 4 tables. Submitted to ApJ

The AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. II. Implications for Nebular Dust Corrections, Nebular SFRs, and Differential Reddening

Authors: Naveen A. Reddy, Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Max Pettini, Natascha M. Forster Schreiber, Charles C. Steidel, Leonardo Clarke, Richard S. Ellis, Anthony J. Pahl, Garth D. Illingworth, Mariska Kriek, Desika Narayanan

Abstract: We discuss the implications of the nebular dust attenuation curves derived for 24 galaxies at z=1.5-4.4 with multiple detections of HI Balmer and Paschen recombination emission lines from the JWST/AURORA survey. The total attenuation of Ha is ~0.20 dex larger on average than the values obtained with the commonly adopted combination of the Balmer decrement and the Galactic extinction curve. Nebular… ▽ More We discuss the implications of the nebular dust attenuation curves derived for 24 galaxies at z=1.5-4.4 with multiple detections of HI Balmer and Paschen recombination emission lines from the JWST/AURORA survey. The total attenuation of Ha is ~0.20 dex larger on average than the values obtained with the commonly adopted combination of the Balmer decrement and the Galactic extinction curve. Nebular-line SFRs and SED-based SFRs are consistent on average when using the MOSDEF attenuation or SMC extinction curves for the latter. The relation between nebular and stellar reddening is consistent with a scenario where the Paschen lines are sensitive to heavily reddened OB associations, while relatively unreddened OB associations contribute significantly to the Balmer line and UV continuum emission. There is a stark contrast between the low Rv (or steepness) of stellar dust attenuation curves and the high Rv (or flatness) of nebular dust attenuation curves. We suggest that the latter could be reflective of a more porous medium established by strong feedback from massive stars. For the youngest galaxy in the sample, the stellar reddening curve is identical to the nebular attenuation curve, in accordance with our expectation that OB associations dominate the stellar continuum emission at all wavelengths for this very young galaxy. Larger samples will be needed to determine whether this conclusion holds for young galaxies in general, and provide further insights into the dust and metals mixing timescale on the scale of HII regions. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Comments: 24 pages, 13 figures, submitted to ApJ, comments welcome

Balmer Decrements and Nebular-Stellar Reddening in JADES Galaxies at $2.7<z<7$

Authors: Shreya Karthikeyan, Leonardo Clarke, Alice E. Shapley, Natalie Lam, Ryan L. Sanders, Naveen A. Reddy, Michael W. Topping, Gabriel B. Brammer

Abstract: We aim to characterize nebular and stellar reddening in star-forming galaxies as a function of global galaxy properties (stellar mass, SFR, metallicity) at $2.7 < z< 7.0$. We also provide a prescription to convert SED-based $E(B-V)_{\mathrm{star}}$ to $E(B-V)_{\mathrm{gas}}$ when direct measurements of nebular reddening are unavailable. Our results are based on JWST/NIRSpec measurements of both in… ▽ More We aim to characterize nebular and stellar reddening in star-forming galaxies as a function of global galaxy properties (stellar mass, SFR, metallicity) at $2.7 < z< 7.0$. We also provide a prescription to convert SED-based $E(B-V)_{\mathrm{star}}$ to $E(B-V)_{\mathrm{gas}}$ when direct measurements of nebular reddening are unavailable. Our results are based on JWST/NIRSpec measurements of both individual spectra, with a sample of 283 galaxies, and composite spectra, including a larger sample of 327 galaxies. We estimate nebular reddening using the Balmer decrement (H$α$/H$β$) above $10^{8.5}$ $M_{\odot}$, where the sample is representative. Stellar reddening and SFRs are derived through Prospector SED fitting, while gas-phase metallicities are estimated from strong emission-line ratios. At fixed stellar mass, Balmer decrements remain consistent within uncertainties across our redshift range, indicating that stellar mass primarily determines the overall dust column even by $z \sim 7$. We find that differential reddening ($ΔE(B-V) \equiv E(B-V)_{\mathrm{gas}} - E(B-V)_{\mathrm{star}}$) scales linearly with mass and SFR at $z \sim 2.7 - 4.0$, but shows no mass or SFR dependence above $z \sim 4.0$. We find evidence for smaller $ΔE(B-V)$ above $z \sim 5.0$, suggesting that nebular emission and stellar continuum probe increasingly similar dust columns towards higher redshift. Finally, we find that nebular reddening correlates strongly with metallicity out to $z \sim 5$, whereas the correlation between stellar reddening and metallicity is weaker or absent. Together, these results suggest that both dust mass and geometry play a significant role in shaping the observed reddening of high-redshift galaxies. △ Less

Submitted 11 March, 2026; originally announced March 2026.

Comments: 19 pages, 8 figures, 2 tables, submitted to ApJ

FRESCO: Constraining Dust Attenuation and Star-Formation Rates of $z\sim 2$ Star-Forming Galaxies with JWST Paschen and Ground-Based Balmer Emission Line Observations

Authors: Michael A. Wozniak, Naveen A. Reddy, Pascal A. Oesch, Ivan Kramarenko, Jorryt Matthee, Chloe Neufeld, Irene Shivaei, Bahram Mobasher, Alice E. Shapley, Brian Siana

Abstract: We present new constraints on dust attenuation and star-formation rates (SFRs) for 77 galaxies at redshifts $z=1.43-2.65$, using Paschen emission line detections from the JWST FRESCO survey and ground-based Balmer line measurements from the MOSDEF survey. Using nebular and continuum emission maps, we find that Paschen emission covers a smaller area than continuum emission observed in the F210M (2.… ▽ More We present new constraints on dust attenuation and star-formation rates (SFRs) for 77 galaxies at redshifts $z=1.43-2.65$, using Paschen emission line detections from the JWST FRESCO survey and ground-based Balmer line measurements from the MOSDEF survey. Using nebular and continuum emission maps, we find that Paschen emission covers a smaller area than continuum emission observed in the F210M (2.1 $μ$m; rest-frame optical) and F444W (4.4 $μ$m; rest-frame near-IR) bands, and is preferentially located toward galaxy outskirts. These results suggest that current star formation is concentrated in regions farther from galaxy centers than older stellar populations traced by the continuum, indicative of inside-out star formation. With a careful accounting of slit-loss corrections for ground-based measurements, we calculate nebular reddening and dust-corrected SFRs using the Balmer decrement (H$α$/H$β$) and Paschen-to-Balmer line ratios (Pa$α$/H$α$ and Pa$β$/H$α$), assuming the Milky Way extinction curve. On average, Paschen-derived reddening and SFRs agree with Balmer-derived values; however, two galaxies exhibit significantly higher Paschen reddening and four show significantly higher Paschen SFRs. We find that non-unity dust covering fractions bias the Balmer decrement toward less reddened OB associations, while decrements involving the Paschen lines are less affected by this bias. These results highlight the enhanced sensitivity of the Paschen lines to the most heavily obscured OB associations in $z\sim2$ galaxies, particularly in galaxies with patchy dust geometries. Future studies using Paschen lines exclusively to measure nebular reddening will yield more robust constraints on the dustiest star-forming regions. △ Less

Submitted 24 February, 2026; originally announced February 2026.

Comments: 25 pages, 16 figures, 2 tables

Bottom-heavy initial mass functions reveal hidden mass in early galaxies

Authors: Chloe M. Cheng, Martje Slob, Mariska Kriek, Aliza G. Beverage, Pieter G. van Dokkum, Rachel Bezanson, Gabriel Brammer, Charlie Conroy, Anna de Graaff, Elham Eftekhari, Robert Feldmann, Wout M. Goesaert, Meng Gu, Joel Leja, Brian Lorenz, Pavel E. Mancera Piña, Ignacio Martín-Navarro, Andrew B. Newman, Sedona H. Price, Alice E. Shapley, Piyush Sharda, Katherine A. Suess, Arjen van der Wel, Daniel R. Weisz

Abstract: JWST observations have revealed that massive galaxies formed and evolved far faster than predicted by galaxy formation models, with many having already assembled a large mass in stars $\sim12$ billion years ago [1-7]. However, masses of distant galaxies are highly uncertain, as they assume a distribution of stellar birth masses (the initial mass function [IMF]) similar to that in the Milky Way (MW… ▽ More JWST observations have revealed that massive galaxies formed and evolved far faster than predicted by galaxy formation models, with many having already assembled a large mass in stars $\sim12$ billion years ago [1-7]. However, masses of distant galaxies are highly uncertain, as they assume a distribution of stellar birth masses (the initial mass function [IMF]) similar to that in the Milky Way (MW). Specifically, the contribution from low-mass stars, which make up the bulk of stellar mass, is not directly observed, but inferred based on an extrapolation of the MW IMF. Here, we provide the first robust measurements of the IMF beyond the local Universe. Using ultra-deep spectra of nine massive, quiescent galaxies at $z\sim0.7$ from the ambitious JWST-IMFERNO program, extended to bluer wavelengths with deep spectra from LEGA-C [8], we find that these distant galaxies have excess low-mass stars. In other words, they have more bottom-heavy IMFs than the MW. For the oldest two galaxies, which are direct descendants of JWST's "impossibly early" galaxies, the bottom-heavy IMFs increase their stellar masses by a factor of $3-4$. These galaxies thus amplify the tension with galaxy formation models. △ Less

Submitted 28 January, 2026; originally announced January 2026.

Comments: 29 pages, 7 figures, under peer review at Nature Astronomy

Emission-line Diagnostics at $z\gtrsim 2$: A Probe of the Ionizing Spectrum and $α$ Enhancement Beyond Cosmic Noon

Authors: Leonardo Clarke, Natalie Lam, Alice E. Shapley, Michael W. Topping, Gabriel B. Brammer, Ryan L. Sanders, Naveen A. Reddy, Shreya Karthikeyan

Abstract: We analyze several key rest-optical emission-line ratios in a sample of 828 galaxies as well as composite spectra from JADES DR3 in the range $1.4 < z < 7$. These emission-line ratios include: [O III]$\lambda5008$/H$β$, [N II]$λ6585$/H$α$, [S II]$λλ6718,6733$/H$α$, [O I]$λ6302$/H$α$, O32, R23, Ne3O2, and RO2Ne3. We find evidence for a harder ionizing spectrum at $z\sim 3.5$ compared to $z\sim 2$ a… ▽ More We analyze several key rest-optical emission-line ratios in a sample of 828 galaxies as well as composite spectra from JADES DR3 in the range $1.4 < z < 7$. These emission-line ratios include: [O III]$\lambda5008$/H$β$, [N II]$λ6585$/H$α$, [S II]$λλ6718,6733$/H$α$, [O I]$λ6302$/H$α$, O32, R23, Ne3O2, and RO2Ne3. We find evidence for a harder ionizing spectrum at $z\sim 3.5$ compared to $z\sim 2$ at fixed gas-phase metallicity, resulting in a pronounced shift in the star-forming galaxy locus on the [N II]/H$α$ BPT diagram and the O32 vs. R23 diagram. At $z\gtrsim 3.5$, star-forming galaxies occupy a common locus, indicating that ISM ionizing conditions at fixed gas-phase metallicity do not evolve strongly at these early cosmic times. There is a connection between ISM ionizing conditions and the chemical abundance patterns (i.e., $α$/Fe) in massive stars providing the ionizing radiation field. Therefore, the lack of evolution in ISM ionizing conditions at $z\gtrsim 3.5$, followed by evolution towards a softer ionizing spectrum at fixed nebular metallicity as cosmic time proceeds to $z\sim 2$ and lower redshift mirrors the chemical abundance patterns in Milky Way stars as a function of iron abundance. Our results highlight the diagnostic power of emission-line diagrams in the era of JWST to further our understanding of the ISM conditions into the Epoch of Reionization. △ Less

Submitted 26 March, 2026; v1 submitted 16 January, 2026; originally announced January 2026.

Comments: 12 pages, 3 figures, 2 tables, accepted for publication in ApJL

Nitrogen abundances in star-forming galaxies 2.2 Gyr after the Big Bang are not elevated

Authors: D. Schaerer, Y. I. Izotov, R. Marques-Chaves, C. C. Steidel, N. Reddy, A. E. Shapley, S. Mascia, J. Chisholm, S. R. Flury, N. Guseva, T. Heckman, A. Henry, A. K. Inoue, I. Jung, H. Kusakabe, K. Mawatari, P. Oesch, G. Oestlin, L. Pentericci, N. Roy, A. Saldana-Lopez, R. Sato, E. Vanzella, A. Verhamme, B. Wang

Abstract: Using deep medium-resolution JWST rest-optical spectra of a sample of typical star-forming galaxies (Lyman break galaxies and Lyman-$α$ emitters) from the LyC22 survey at $z \sim 3$, we determined the nebular abundances of N, O, and Ne relative to H for a subsample of 25 objects with the direct method, based on auroral [OIII]4363 line detections. Our measurements increases the number of accurate N… ▽ More Using deep medium-resolution JWST rest-optical spectra of a sample of typical star-forming galaxies (Lyman break galaxies and Lyman-$α$ emitters) from the LyC22 survey at $z \sim 3$, we determined the nebular abundances of N, O, and Ne relative to H for a subsample of 25 objects with the direct method, based on auroral [OIII]4363 line detections. Our measurements increases the number of accurate N/O determinations at $z \sim 2-4$ using a homogeneous approach. We found a mean value of $\log({\rm N/O})=-1.29^{+0.25}_{-0.21} $ over a metallicity range 12+log(O/H)=7.5 to 8.44. The observed N/O ratio and scatter are indistinguishable from that observed in low-z galaxies and HII regions over the same metallicity range, showing thus no redshift evolution of N/O for typical galaxies over a significant fraction of cosmic time. We also show that typical $z \sim 3$ galaxies show a similar offset in the BPT diagram as galaxies from the low-z Lyman Continuum Survey (LzLCS), when compared to the average of SDSS galaxies, and show that this offset is not due to enhanced nitrogen abundances. Our results establish a basis for future studies of the evolution of N and O at higher redshifts. △ Less

Submitted 11 January, 2026; originally announced January 2026.

Comments: 7 pages, 5 figures. Submitted to Astronomy and Astrophysics (after 1st revision)

Journal ref: A&A 708, A242 (2026)

The JWST EXCELS survey: Outflows in 1.5 < z < 5 quiescent and recently quenched galaxies are likely relics from episodic AGN activity

Authors: Elizabeth Taylor, Adam C. Carnall, David Maltby, Omar Almaini, Ho-Hin Leung, Struan D. Stevenson, Andrea Negri, Fergus Cullen, Vivienne Wild, Ross J. McLure, Alice E. Shapley, Karla Z. Arellano-Córdova, Ryan Begley, Cecilia Bondestam, Thomas de Lisle, Callum T. Donnan, James S. Dunlop, Richard Ellis, Guillaume Hewitt, Anton M. Koekemoer, Feng-Yuan Frey Liu, Derek J. McLeod, Kate Rowlands, Ryan L. Sanders, Dirk Scholte , et al. (2 additional authors not shown)

Abstract: We investigate the presence and origin of neutral gas outflows and inflows in 13 post-starburst (PSB) and quiescent galaxies at redshifts 1.8 $\leq$ z $\leq$ 4.6, using JWST NIRSpec spectroscopy from the EXCELS survey. NaD absorption profiles reveal that 3 out of 13 exhibit blueshifted absorption indicative of outflows, and a further 2 objects show signs of inflowing gas. Outflow velocities range… ▽ More We investigate the presence and origin of neutral gas outflows and inflows in 13 post-starburst (PSB) and quiescent galaxies at redshifts 1.8 $\leq$ z $\leq$ 4.6, using JWST NIRSpec spectroscopy from the EXCELS survey. NaD absorption profiles reveal that 3 out of 13 exhibit blueshifted absorption indicative of outflows, and a further 2 objects show signs of inflowing gas. Outflow velocities range from $\approx$ 300 - 1200 kms$^{-1}$, and we find gas flows are detected exclusively in objects that quenched $\lt$ 600 Myr ago. This result holds when we include comparable objects from recent literature. We derive mass outflow rates over two orders of magnitude higher than current levels of star formation in our sample, indicating that the winds are unlikely to be driven by supernovae, and likely play a significant role in keeping the galaxies quenched. The majority of the outflow sample have anomalously high energy and momentum outflow rates compared to those predicted for current levels of star formation or AGN activity. We conclude that we are likely observing fossil outflows driven by previous, more luminous AGN activity which has since faded. We then compare with the EAGLE simulation to explore a potential 'outflow cycle', finding that our observations are consistent with a model in which z $\sim$ 3 quiescent galaxies undergo short $\simeq$ 5 Myr periods of AGN activity strong enough to drive outflows, which occur every $\simeq$ 40 Myr on average. This AGN activity drives observable outflows that persist for up to $\simeq$ 10 Myr after the AGN fades, followed by a $\simeq$ 20 Myr lull, and a subsequent short inflow, which eventually re-ignites AGN activity, and the cycle repeats. △ Less

Submitted 12 May, 2026; v1 submitted 5 January, 2026; originally announced January 2026.

Comments: 22 pages, 12 figures. Accepted for publication in MNRAS

Dynamical properties and star formation history of a low-mass quenched galaxy at Cosmic Noon

Authors: K. Ito, F. Valentino, W. M. Baker, G. Brammer, R. Gottumukkala, T. Kakimoto, C. D. P. Lagos, M. Onodera, A. Pensabene, G. Scarpe, M. Tanaka, K. E. Whitaker, N. A. Reddy, R. L. Sanders, A. E. Shapley

Abstract: We present the spectroscopic confirmation and in-depth analysis of AURORA-LQG1, a low-mass quiescent galaxy at $z_{\rm spec}=2.0834$ with $\log(M_\star/M_\odot)=9.6$ observed with medium-resolution JWST/NIRSpec spectroscopy. The deep medium-resolution spectrum enables the measurement of its stellar velocity dispersion ($σ_\star = 95_{-33}^{+38}\,{\rm km\,s^{-1}}$), the smallest value recorded amon… ▽ More We present the spectroscopic confirmation and in-depth analysis of AURORA-LQG1, a low-mass quiescent galaxy at $z_{\rm spec}=2.0834$ with $\log(M_\star/M_\odot)=9.6$ observed with medium-resolution JWST/NIRSpec spectroscopy. The deep medium-resolution spectrum enables the measurement of its stellar velocity dispersion ($σ_\star = 95_{-33}^{+38}\,{\rm km\,s^{-1}}$), the smallest value recorded among spectroscopically confirmed quiescent galaxies at $z\sim2$. Coupled with a compact size ($0.41\pm0.03\, {\rm kpc}$), it yields a dynamical mass estimate of $\log(M_{\rm dyn}/M_\odot)=9.75_{-0.38}^{+0.29}$. Its star formation history suggests that half of the stellar mass was in place $\sim1\,{\rm Gyr}$ before the observed epoch, with quenching occurring $\sim0.2\,{\rm Gyr}$ prior to $z=2.08$. These results confirm that AURORA-LQG1 is genuinely quenched, rather than in a temporary phase of suppressed star formation rate. AURORA-LQG1 is consistent with the mass fundamental plane at $z\sim2$, previously constrained only by massive quiescent systems. Compared with more massive counterparts at the same epoch observed with NIRSpec grating spectroscopy, the time since quenching for AURORA-LQG1 is among the shortest observed. The galaxy resides in a possible dense group-scale ($\sim50$ kpc) environment containing one companion with tentative spectroscopic redshift and five companion candidates, and it is embedded in a known protocluster on Mpc scales. A potential environmental influence on its evolution could explain the outside-in quenching suggested by the positive gradient of size with wavelength. This study demonstrates that deep JWST/NIRSpec spectroscopy enables low-mass quiescent galaxies at Cosmic Noon to be characterized with a level of detail long reserved for massive systems, offering valuable new insights into how quenching operates in these underexplored low-mass systems. [Abridged] △ Less

Submitted 4 January, 2026; originally announced January 2026.

Comments: 10 pages, 7 figures, 1 table + Appendix. submitted to A&A

Journal ref: A&A 710, A122 (2026)

The AURORA Survey: The Mass -- Metallicity and Fundamental Metallicity Relations at $z \sim 2.3$ Based Purely on Direct $T_e$ Metallicities

Authors: Ali Ahmad Khostovan, Ryan L. Sanders, Alice E. Shapley, Michael W. Topping, Naveen A. Reddy, Alex M. Garcia, Danielle A. Berg, Leonardo Clarke, Fergus Cullen, Richard S. Ellis, N. M. Förster Schreiber, Karl Glazebrook, Tucker Jones, Derek J. McLeod, Anthony J. Pahl, Max Pettini, Paul Torrey

Abstract: We present new constraints on the Mass -- Metallicity (MZR) and Fundamental Metallicity Relations (FMR) using a sample of 34 galaxies at $1.38\leq~z\leq~3.5$ (median $z=2.28$). These galaxies have direct $T_e$ measurements from [O\sc{iii}]4363Å~and/or [O\sc{ii}]7320,7331Å~auroral emission lines detected with \textit{JWST}/NIRSpec as part of the AURORA survey. The detection of both oxygen auroral l… ▽ More We present new constraints on the Mass -- Metallicity (MZR) and Fundamental Metallicity Relations (FMR) using a sample of 34 galaxies at $1.38\leq~z\leq~3.5$ (median $z=2.28$). These galaxies have direct $T_e$ measurements from [O\sc{iii}]4363Å~and/or [O\sc{ii}]7320,7331Å~auroral emission lines detected with \textit{JWST}/NIRSpec as part of the AURORA survey. The detection of both oxygen auroral lines allows for dual-zone direct $T_e$ measurements and expands the dynamic range in $12+\log\mathrm{(O/H)}$ (7.68 to 8.65 dex), stellar mass ($10^{8}$ to $10^{10.4}$ M$_\odot$), and star-formation rate ($1$ to $100$ M$_\odot$ yr$^{-1}$) compared to previous direct $T_e$ studies of the high-redshift MZR and FMR. We characterize the $z\sim2$ MZR and find a slope of $0.27\pm0.04$ and normalization of $12+\log\mathrm{(O/H)} = 8.44\pm0.04$ at $10^{10}$ M$_\odot$ with an intrinsic scatter of 0.10 dex, consistent with past strong-line MZR measurements. Comparisons with $z\sim2$ predictions from six simulations reveal that none reproduce our observed MZR normalization evolution between $z\sim0$ and $z\sim2$. This discrepancy suggests current models do not fully capture the chemical enrichment and feedback processes occurring at cosmic noon. However, all 34 galaxies are on or above the star-forming main sequence such that our sample may be biased towards lower $12+\log\mathrm{(O/H)}$ if the FMR persists at $z\sim2$. Correcting for this selection effect would increase O/H by $\approx0.1$ dex at 10$^{9.3}$ M$_\odot$ (the median mass of our sample) bringing our MZR into better agreement with that of \texttt{TNG}. Lastly, we find our $z\sim2.3$ sample is consistent with the $z\sim0$ FMR within 0.1 dex in O/H, indicating that the smooth secular mechanisms regulating chemical enrichment, star formation, stellar mass, and outflows were in place at cosmic noon. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: 12 pages, 4 figures, submitted to ApJL. We welcome any comments and feedback

The AURORA Survey: Constraining Chemical Enrichment Pathways at Cosmic Noon with Argon Abundances

Authors: Jack Foley, Alice Shapley, Ryan Sanders, Naveen A. Reddy, Michael W. Topping, Thomas M. Stanton, Max Pettini, Fergus Cullen, Richard S. Ellis, N. M. Förster Schreiber, Tucker Jones, Anthony J. Pahl, Leonardo Clarke, Natalie Lam

Abstract: 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 $α-$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 $α-$elemen… ▽ More 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 $α-$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 $α-$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]$\lambda7137$ emission line relative to the [OIII]$\lambda5008$ emission line. With this calibration, we estimate argon abundances (Ar/O) of $0.42^{+0.12}_{-0.10}\mbox{(Ar/O)}_{\odot}$ for the $\langle z \rangle = 2.26$ bin and $0.42^{+0.12}_{-0.11}\mbox{(Ar/O)}_{\odot}$ for the $\langle z \rangle = 3.15$ bin, suggesting minimal SNe Ia and dominant CCSNe enrichment in this sample. Comparison of our abundance measurements of $z\sim 2-3$ 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., 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. △ Less

Submitted 10 June, 2026; v1 submitted 10 December, 2025; originally announced December 2025.

Comments: 19 pages, 4 figures, 1 table, accepted to ApJ

The JWST EXCELS Survey: gas-phase metallicity evolution at 2 < z < 8

Authors: T. M. Stanton, F. Cullen, A. C. Carnall, D. Scholte, K. Z. Arellano-Córdova, A. E. Shapley, D. J. McLeod, C. T. Donnan, R. Begley, R. Davé, J. S. Dunlop, R. J. McLure, K. Rowlands, C. Bondestam, M. L. Hamadouche, H. -H. Leung, S. D. Stevenson, E. Taylor

Abstract: We present an analysis of the gas-phase mass-metallicity relationship (MZR) and fundamental metallicity relationship (FMR) for $65$ star-forming galaxies at $2 < z < 8$ from the JWST/EXCELS survey. We calculate gas-phase metallicities (12 + log(O/H)) using strong-line calibrations explicitly tested against the EXCELS sample, and report direct-method metallicities for $19$ galaxies. Our sample span… ▽ More We present an analysis of the gas-phase mass-metallicity relationship (MZR) and fundamental metallicity relationship (FMR) for $65$ star-forming galaxies at $2 < z < 8$ from the JWST/EXCELS survey. We calculate gas-phase metallicities (12 + log(O/H)) using strong-line calibrations explicitly tested against the EXCELS sample, and report direct-method metallicities for $19$ galaxies. Our sample spans $8.1<\log(\rm M_\star/M_\odot)<10.3$ and $0<\log(\rm SFR/M_\odot \, yr^{-1})<2$, consistent with main-sequence star-forming galaxies at the same redshifts. We find a clear MZR at both $2<z<4$ ($\langle z \rangle = 3.2$) and $4<z<8$ ($\langle z \rangle = 5.5$), with consistent slopes and mild evolution in normalization of $\simeq 0.1 \, \mathrm{dex}$, matching trends from simulations and recent observations. Our results demonstrate rapid gas-phase enrichment in the early Universe; galaxies at $z \simeq 3$ (within the first $\simeq 15$ per cent of cosmic time) are enriched to $\simeq 40$ per cent of the metallicity of equivalent mass galaxies at $z=0$. We find tentative evidence for SFR-dependence in the MZR scatter, though results remain inconclusive and highlight the need for larger high-redshift samples. Comparison with locally derived FMRs reveals a clear offset consistent with other $z > 3$ studies. We discuss potential drivers of this offset, noting that high-redshift samples have significantly different physical properties compared to local samples used to define the $z=0$ FMR. Our results confirm that low-mass, high specific star-formation rate galaxies common at high redshift are inconsistent with the equilibrium conditions underlying the local FMR, and highlight the rapid chemical enrichment at early cosmic epochs. △ Less

Submitted 4 March, 2026; v1 submitted 1 November, 2025; originally announced November 2025.

Comments: 24 pages, 16 figures, 3 tables. Accepted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2026)

The AURORA Survey: Ionizing Photon Production Efficiency with Minimal Nebular Dust Attenuation Systematics

Authors: Anthony J. Pahl, Alice Shapley, Naveen A. Reddy, Ryan Sanders, Michael W. Topping, Danielle A. Berg, Callum T. Donnan, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, K. Glazebrook, Derek J. McLeod, Max Pettini, Daniel Schaerer

Abstract: We present ionizing photon production efficiencies ($ξ_{\rm ion}$) for 63 z=1.5-6.9 star-forming galaxies using precise nebular dust attenuation corrections from the JWST/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… ▽ More We present ionizing photon production efficiencies ($ξ_{\rm ion}$) for 63 z=1.5-6.9 star-forming galaxies using precise nebular dust attenuation corrections from the JWST/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 $ξ_{\rm ion}$ and redshift, equivalent width of [OIII]$λ$5007, and O32=[OIII]$λ$5007/[OII]$λ$3726,3729, and negative correlations between $ξ_{\rm ion}$ and stellar attenuation, UV luminosity (L$_{\rm UV}$), 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 relationships between $ξ_{\rm ion}$ and galaxy property, notably inducing a flat trend between $ξ_{\rm ion}$ and L$_{\rm UV}$ 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 dust systematics on $ξ_{\rm ion}$ for inclusion in reionization models. △ Less

Submitted 14 October, 2025; originally announced October 2025.

Comments: 20 pages, 7 figures, submitted to ApJ

The Star-forming Main Sequence and Bursty Star-formation Histories at $z>1.4$ in JADES and AURORA

Authors: Leonardo Clarke, Alice E. Shapley, Natalie Lam, Michael W. Topping, Gabriel B. Brammer, Ryan L. Sanders, Naveen A. Reddy, Shreya Karthikeyan

Abstract: 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 $10^{8.5}\rm\ M_\odot$ where the sample is largely representative, estimating star-formation rates (SFRs) using the H$α$ line flux and rest-frame far UV (160… ▽ More 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 $10^{8.5}\rm\ M_\odot$ where the sample is largely representative, estimating star-formation rates (SFRs) using the H$α$ 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 ($σ_{\rm int}$) increases with decreasing stellar mass for the H$α$-based SFMS, and we find no mass dependence of $σ_{\rm int}$ in the UV-based SFMS. Additionally, we find that $σ_{\rm int}$ decreases with increasing redshift, from $0.36^{+0.02}_{-0.02}$ dex to $0.22^{+0.08}_{-0.07}$ dex (H$α$ SFMS), and from $0.28^{+0.02}_{-0.02}$ dex to $0.20^{+0.08}_{-0.07}$ dex (UV SFMS) between $z\sim2$ and $z\sim 6.5$. We also measure the redshift evolution of the specific SFR and find that, assuming $\rm sSFR\propto (1+z)^γ$, $γ=1.89^{+0.16}_{-0.15}$ for the H$α$-based SFMS, and $γ=1.36^{+0.13}_{-0.13}$ for the UV-based SFMS. Analyzing the observed H$α$/UV luminosity ratios and star-formation histories from the {\sc 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 $\rm L_{Hα}/νL_{ν,1600}$ vs. $Δ\rm \log(L_{Hα})$. 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. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Comments: 40 pages, 13 figures, 3 tables. Submitted to ApJ

The JWST EXCELS Survey: A spectroscopic investigation of the ionizing properties of star-forming galaxies at 1<z<8

Authors: R. Begley, R. J. McLure, F. Cullen, A. C. Carnall, T. M. Stanton, D. Scholte, D. J. McLeod, J. S. Dunlop, K. Z. Arellano-Córdova, C. Bondestam, C. T. Donnan, M. L. Hamadouch, A. E. Shapley, S. Stevenson

Abstract: Charting the Epoch of Reionization demands robust assessments of what drives the production of ionizing photons in high-redshift star-forming galaxies (SFGs), and requires better predictive capabilities from current observations. Using a sample of $N=159$ SFGs at $1<z<8$, observed with deep medium-resolution spectroscopy from the JWST/NIRSpec EXCELS survey, we perform a statistical analysis of the… ▽ More Charting the Epoch of Reionization demands robust assessments of what drives the production of ionizing photons in high-redshift star-forming galaxies (SFGs), and requires better predictive capabilities from current observations. Using a sample of $N=159$ SFGs at $1<z<8$, observed with deep medium-resolution spectroscopy from the JWST/NIRSpec EXCELS survey, we perform a statistical analysis of their ionizing photon production efficiencies ($ξ_\rm{ion}$). We consider $ξ_\rm{ion}$, measured with Balmer line measurements, in relation to a number of key galaxy properties including; nebular emission line strengths ($W_λ(\rm{Hα})$ and $W_λ$( [OIII])), UV luminosity ($M_\rm{UV}$) and UV slope ($β_\rm{UV}$), as well as dust attenuation ($E(B-V)_\rm{neb}$) and redshift. Implementing a Bayesian linear regression methodology, we fit $ξ_\rm{ion}$ against the principal observables while fully marginalising over all measurement uncertainties, mitigating against the impact of outliers and determining the intrinsic scatter. Significant relations between $ξ_\rm{ion}$ and $ W_λ(\rm{Hα})$, $W_λ$([OIII]) and $β_\rm{UV}$ are recovered. Moreover, the weak trends with $M_\rm{UV}$ and redshift can be fully explained by the remaining property dependencies. Expanding our analysis to multivariate regression, we determine that $W_λ(\rm{Hα})$ or $W_λ$([OIII]), along with $β_\rm{UV}$ and $E(B-V)_\rm{neb}$, are the most important observables for accurately predicting $ξ_\rm{ion,0}$. The latter identifies the most common outliers as SFGs with relatively high $E(B-V)_\rm{neb}\gtrsim0.5$, possibly indicative of obscured star-formation or strong differential attenuation. Combining these properties enable $ξ_\rm{ion,0}$ to be inferred with an accuracy of $\sim0.15\,$dex, with a population intrinsic scatter of $σ_\rm{int}\sim0.035\,$dex. △ Less

Submitted 1 December, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: 20 pages, 14 figures + 1 appendix. Accepted to MNRAS

Journal ref: Mon Not R Astron Soc (2025)

NEXUS: A Search for Nuclear Variability with the First Two JWST NIRCam Epochs

Authors: Zachary Stone, Yue Shen, Ming-Yang Zhuang, Lei Hu, Justin Pierel, Junyao Li, Adam J. Burgasser, Jenny E. Greene, Zhiwei Pan, Alice E. Shapley, Fengwu Sun, Padmavathi Venkatraman, Feige Wang

Abstract: 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 $\sim 25\,$k 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 $1σ$ va… ▽ More 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 $\sim 25\,$k 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 $<25$th 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 $z_{\rm phot}>10$. 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 $3\lesssim z \lesssim 7$, and find none of them show detectable variability in either band. We derive stringent $3σ$ upper limits on the F444W variability of $\sim 3-10\%$ for these LRDs, with a median value of $\sim 5\%$. These constraints imply weak variability in the rest-frame optical continuum of LRDs. △ Less

Submitted 26 July, 2026; v1 submitted 23 September, 2025; originally announced September 2025.

Comments: 16 pages, 10 figures, 1 table. Accepted into ApJ. The source catalog can be accessed here: https://ariel.astro.illinois.edu/nexus/paper_data/nuclear_variability/nexus_wide01_deep01_stacked_sources_allband.fits.gz

Journal ref: ApJ 1006 106 (2026)

The JWST EXCELS survey: Insights into the nature of quenching at cosmic noon

Authors: Maya Skarbinski, Kate Rowlands, Katherine Alatalo, Vivienne Wild, Adam C. Carnall, Omar Almaini, David Maltby, Thomas de Lisle, Timothy Heckman, Ryan Begley, Fergus Cullen, James S. Dunlop, Guillaume Hewitt, Ho-Hin Leung, Derek McLeod, Ross McLure, Justin Atsushi Otter, Pallavi Patil, Andreea Petric, Alice E. Shapley, Struan Stevenson, Elizabeth Taylor

Abstract: We study 24 massive quiescent galaxies with $\log \textrm{M}_*/\textrm{M}_\odot > 10$ 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 ($100\textrm{ M}_{\odot} \textrm{yr}^{-1} -1000 \textrm{ M}_{\odot} \textrm{yr}^{-1}$), follo… ▽ More We study 24 massive quiescent galaxies with $\log \textrm{M}_*/\textrm{M}_\odot > 10$ 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 ($100\textrm{ M}_{\odot} \textrm{yr}^{-1} -1000 \textrm{ M}_{\odot} \textrm{yr}^{-1}$), 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 $\sim600$ Myr, with more massive galaxies ($\log \textrm{M}_*/\textrm{M}_\odot > 10.7$) 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 AGN activity in 4 out of the 8 galaxies with robust emission line detections, based on line ratio diagnostics. Our findings suggest that there are 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. △ Less

Submitted 13 February, 2026; v1 submitted 22 September, 2025; originally announced September 2025.

Comments: Accepted for publication in The Astrophysical Journal

PRIMER & JADES reveal an abundance of massive quiescent galaxies at 2 < z < 5

Authors: Struan D. Stevenson, Adam C. Carnall, Ho-Hin Leung, Elizabeth Taylor, Fergus Cullen, James S. Dunlop, Derek J. McLeod, Ross J. McLure, Ryan Begley, Karla Z. Arellano-Córdova, Laia Barrufet, Cecilia Bondestam, Callum T. Donnan, Richard S. Ellis, Norman A. Grogin, Anton M. Koekemoer, Feng-Yuan Liu, Pablo G. Pérez-González, Kate Rowlands, Ryan L. Sanders, Dirk Scholte, Alice E. Shapley, Maya Skarbinski, Thomas M. Stanton, Vivienne Wild

Abstract: We select a mass-complete sample of 225 quiescent galaxies at $z>2$ with $M_* > 10^{10}\ \mathrm{M}_\odot$ from PRIMER and JADES photometry spanning a total area of $\simeq320$ sq. arcmin. We restrict our analysis to only area with optical coverage in three $HST$ ACS filters, and provide evidence that this is important for selecting the most complete and clean samples of $z>2$ massive quiescent ga… ▽ More We select a mass-complete sample of 225 quiescent galaxies at $z>2$ with $M_* > 10^{10}\ \mathrm{M}_\odot$ from PRIMER and JADES photometry spanning a total area of $\simeq320$ sq. arcmin. We restrict our analysis to only area with optical coverage in three $HST$ ACS filters, and provide evidence that this is important for selecting the most complete and clean samples of $z>2$ massive quiescent galaxy candidates. We investigate the contamination in our sample via $JWST$ NIRSpec spectroscopic validation, $Chandra$ X-ray imaging, and ALMA interferometry, calculating a modest total contamination fraction of $12.9_{-3.1}^{+4.0}$ per cent. The removal of $HST$ data increases star-forming galaxy contamination by $\simeq10$ per cent and results in a $\simeq20$ 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 galaxy evolution simulations, we find that most can now reproduce the observed massive quiescent galaxy number density at $2<z<3$, however they still increasingly fall short at $z>3$, with discrepancies of up to $\simeq 1$ 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. We find a very high incidence of faint AGN in our sample, at a level of $\simeq50$ 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 quenched galaxies from re-igniting star formation. To properly characterise the evolution of early massive quiescent galaxies, greater coverage in optical filters and significantly larger spectroscopic samples will be required. △ Less

Submitted 8 December, 2025; v1 submitted 8 September, 2025; originally announced September 2025.

Comments: 23 pages, 15 figures

Journal ref: Mon Not R Astron Soc (2025)

JWST Spectroscopic Insights Into the Diversity of Galaxies in the First 500 Myr: Short-Lived Snapshots Along a Common Evolutionary Pathway

Authors: Guido Roberts-Borsani, Pascal Oesch, Richard Ellis, Andrea Weibel, Emma Giovinazzo, Rychard Bouwens, Pratika Dayal, Adriano Fontana, Kasper Heintz, Jorryt Matthee, Romain Meyer, Laura Pentericci, Alice Shapley, Sandro Tacchella, Tommaso Treu, Fabian Walter, Hakim Atek, Sownak Bose, Marco Castellano, Yoshinobu Fudamoto, Takahiro Morishita, Rohan Naidu, Ryan Sanders, Arjen van der Wel

Abstract: We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at z>10 with JWST/NIRSpec prism observations. We compare the properties of strong UV line emitters, traced by intense CIV emission, with those of more "typical" sources with weak or undetected CIV. The more typical (or "CIV-weak") sources reveal significant scatter in their CIII] line strengths, UV… ▽ More We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at z>10 with JWST/NIRSpec prism observations. We compare the properties of strong UV line emitters, traced by intense CIV emission, with those of more "typical" sources with weak or undetected CIV. The more typical (or "CIV-weak") sources reveal significant scatter in their CIII] line strengths, UV continuum slopes, and physical sizes, spanning CIII] equivalent widths of ~1-51 Å, UV slopes of $β$~-1.6 to -2.6, and half-light radii of ~50-1000 pc. In contrast, CIV-strong sources occupy the tail of these distributions, with CIII] EWs of 16-51 Å, UV slopes $β$<-2.5, compact morphologies ($r_{50}$<100 pc), and elevated star formation surface densities ($Σ_{SFR}$>100 $M_{\odot}yr^{-1}kpc^{-2}$). 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 timescales (<3 Myr), with strong CIV emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong CIV and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that AGN are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionisation 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. △ Less

Submitted 13 April, 2026; v1 submitted 29 August, 2025; originally announced August 2025.

Comments: 21 pages, 13 figures. Accepted for publication in MNRAS

A Uniform Analysis of Gas-phase Metallicity Evolution with 1-3 Gyr Time Sampling over the Past 12 Billion Years

Authors: Shweta Jain, Ryan L. Sanders, Ali Ahmad Khostovan, Tucker Jones, Alice E. Shapley, Naveen A. Reddy, Alex M. Garcia, Paul Torrey, Alison Coil

Abstract: 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 $z\sim0$ to $z\sim3.3$. We present new Keck/DEIMOS measurements of the [OII]$λ\lambda3726,3729$ emission line doublet for star-forming galaxies at $z\sim1.5$ with existing measurements of redder rest-optical… ▽ More 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 $z\sim0$ to $z\sim3.3$. We present new Keck/DEIMOS measurements of the [OII]$λ\lambda3726,3729$ emission line doublet for star-forming galaxies at $z\sim1.5$ with existing measurements of redder rest-optical lines from the MOSDEF survey. These new observations enable uniform estimation of the gas-phase oxygen abundance using ratios of the [OII], H$β$, and [OIII] lines for mass-binned samples of star-forming galaxies in 6 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 $γ=0.28\pm0.01$, implying the outflow metal loading factor ($ζ_\text{out}=\frac{Z_{\text{out}}}{Z_{\text{ISM}}}\frac{\dot{M}_{\text{out}}}{\text{SFR}}$) scales approximately as $\rm ζ_{out}\propto M_*^{-0.3}$ out to at least $z\sim3.3$. The normalization of the MZR at $10^{10}\ \text{M}_\odot$ decreases with increasing redshift at a rate of $d\log(\text{O/H})/dz =-0.11\pm0.01$ across the full redshift range. We find that any evolution of the FMR is smaller than 0.1 dex out to $z\sim3.3$. 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. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 28 pages, 12 figures, Submitted to ApJ

The AURORA Survey: High-Redshift Empirical Metallicity Calibrations from Electron Temperature Measurements at z=2-10

Authors: Ryan L. Sanders, Alice E. Shapley, Michael W. Topping, Naveen A. Reddy, Danielle A. Berg, Ali Ahmad Khostovan, Rychard J. Bouwens, Gabriel Brammer, Adam C. Carnall, Fergus Cullen, Romeel Davé, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, Steven R. Furlanetto, Karl Glazebrook, Garth D. Illingworth, Tucker Jones, Mariska Kriek, Derek J. McLeod, Ross J. McLure, Desika Narayanan, Pascal A. Oesch, Anthony J. Pahl, Max Pettini , et al. (7 additional authors not shown)

Abstract: We present detections of auroral emission lines of [OIII], [OII], [SIII], and [SII] 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… ▽ More We present detections of auroral emission lines of [OIII], [OII], [SIII], and [SII] 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$_\odot$. 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 $α$ 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 $z\sim0$ galaxy and HII 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. △ Less

Submitted 19 May, 2026; v1 submitted 13 August, 2025; originally announced August 2025.

Comments: 29 pages + 10 pages appendix/references, accepted to ApJ

The AURORA Survey: Robust Helium Abundances at High Redshift Reveal A Subpopulation of Helium-Enhanced Galaxies in the Early Universe

Authors: Danielle A. Berg, Ryan L. Sanders, Alice E. Shapley, Michael W. Topping, Naveen A. Reddy, Evan D. Skillman, Erik Aver, Fergus Cullen, Callum T. Donnan, James S. Dunlop, Tucker Jones, Ali Ahmad Khostovan, Derek J. McLeod, Desika Narayanan, Pascal A. Oesch, Anthony J. Pahl, Max Pettini, N. M. Förster Schreiber, Daniel P. Stark

Abstract: We present the first robust helium (He) abundance measurements in star-forming galaxies at redshifts $1.6\lesssim z\lesssim 3.3$ using deep, moderate-resolution JWST/NIRSpec spectroscopy from the AURORA survey. We establish a High$-z$ HeI Sample consisting of 20 galaxies with multiple high-S/N ($>5σ$) HeI emission-line detections, including the critical near-infrared $λ$10833 line. This is the fir… ▽ More We present the first robust helium (He) abundance measurements in star-forming galaxies at redshifts $1.6\lesssim z\lesssim 3.3$ using deep, moderate-resolution JWST/NIRSpec spectroscopy from the AURORA survey. We establish a High$-z$ HeI Sample consisting of 20 galaxies with multiple high-S/N ($>5σ$) HeI emission-line detections, including the critical near-infrared $λ$10833 line. This is the first study at high redshift leveraging $λ$10833 to break degeneracies between temperature, electron density, optical depth, and He$^+$/H$^+$, enabling reliable He abundance determinations in the early universe. We use a custom MCMC framework incorporating direct-method electron temperature priors, extended optical depth ($τ_{\lambda3890}$) model grids up to densities of $10^6$~cm$^{-3}$, and simultaneous fits of the physical conditions and HeI/HI line ratios to derive ionic He$^+$/H$^+$ abundances. Most of the AURORA galaxies follow the extrapolated $z\sim0$ He/H-O/H trend, indicating modest He enrichment by $z\sim2-3$. However, we identify a subpopulation of four galaxies that exhibit elevated He mass fractions ($ΔY>0.03$) without corresponding enhancements in N/O or $α$-elements ($\sim20$% of the sample). This abundance pattern is inconsistent with enrichment from asymptotic giant branch stars, but favors early He enrichment from very massive stars (VMSs; $M\gtrsim100\ M_\odot$), 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 HeI spectroscopy for tracing early stellar feedback, enrichment pathways, and GC progenitor signatures in the high-z universe. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Comments: 29 pages, 11 figures, 4 tables, submitted to ApJ

MOSDEF-3D: Keck/OSIRIS Maps of the Ionized ISM in $z \sim 2$ Galaxies

Authors: Natalie Lam, Alice E. Shapley, Ryan L. Sanders, Tuan Do, Tucker Jones, Alison Coil, Mariska Kriek, Bahram Mobasher, Naveen A. Reddy, Brian Siana, Leonardo Clarke

Abstract: We present spatially-resolved rest-frame optical emission line maps of four galaxies at $z \sim 2$ observed with Keck/OSIRIS to study the physical conditions of the ISM at Cosmic Noon. Our analysis of strong emission line ratios in these galaxies reveals an offset from the local star-forming locus on the BPT diagram, but agrees with other star-forming galaxies at similar redshifts. Despite the off… ▽ More We present spatially-resolved rest-frame optical emission line maps of four galaxies at $z \sim 2$ observed with Keck/OSIRIS to study the physical conditions of the ISM at Cosmic Noon. Our analysis of strong emission line ratios in these galaxies reveals an offset from the local star-forming locus on the BPT diagram, but agrees with other star-forming galaxies at similar redshifts. Despite the offset towards higher [O III]$\lambda5008$/H$β$ and [N II]$\lambda6585$/H$α$, these strong-line ratios remain consistent with or below the maximum starburst threshold even in the inner $\sim 1$ kpc region of the galaxies, providing no compelling evidence for central AGN activity. The galaxies also exhibit flat radial gas-phase metallicity gradients, consistent with previous studies of $z \sim 2$ galaxies and suggesting efficient radial mixing possibly driven by strong outflows from intense star formation. Overall, our results reveal the highly star-forming nature of these galaxies, with the potential to launch outflows that flatten metallicity gradients through significant radial gas mixing. Future observations with JWST/NIRSpec are crucial to detect fainter emission lines at higher spatial resolution to further constrain the physical processes and ionization mechanisms that shape the ISM during Cosmic Noon. △ Less

Submitted 26 March, 2026; v1 submitted 27 June, 2025; originally announced June 2025.

Comments: 34 pages, 23 figures, 1 table. Accepted for publication in ApJ

REBELS-MOSFIRE: Weak CIII] Emission is Typical Among Extremely UV-bright, Massive Galaxies at $z\sim7$

Authors: Ryan Endsley, Alice E. Shapley, Michael W. Topping, Daniel P. Stark, Rychard J. Bouwens, Lucie E. Rowland, Laura Sommovigo, Hiddo S. B. Algera, Manuel Aravena, Rebecca A. A. Bowler, Elisabete da Cunha, Ilse de Looze, Andrea Ferrara, Rebecca Fisher, Valentino González, Hanae Inami, Themiya Nanayakkara, Sander Schouws, Mengtao Tang

Abstract: 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 REBELS-MOSFIRE 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… ▽ More 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 REBELS-MOSFIRE 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-MOSFIRE 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. △ Less

Submitted 17 January, 2026; v1 submitted 26 June, 2025; originally announced June 2025.

Comments: 16 pages, 4 figures, accepted to ApJ

The JWST/AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. I. A Diversity of Nebular Attenuation Curves and Evidence for Non-Unity Dust Covering Fractions

Authors: Naveen A. Reddy, Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Richard S. Ellis, Max Pettini, Gabriel Brammer, Fergus Cullen, Natascha M. Forster Schreiber, Ali A. Khostovan, Derek J. McLeod, Ross J. McLure, Desika Narayanan, Pascal A. Oesch, Anthony J. Pahl, Charles C. Steidel, Danielle A. Berg

Abstract: 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 heavi… ▽ More 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 heavily reddened 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 reddened and unreddened 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. △ Less

Submitted 13 May, 2026; v1 submitted 20 June, 2025; originally announced June 2025.

Comments: 30 pages, 28 figures, 1 table; published 2026 February 20

Journal ref: ApJ, 999, 15 (2026)

The AURORA Survey: Tracing Galactic Outflows at $z\gtrsim2.5$ with JWST/NIRSpec NUV Absorption Lines

Authors: Emily Kehoe, Alice E. Shapley, Ryan L. Sanders, Naveen A. Reddy, Natalie Lam, Leonardo Clarke, Fergus Cullen, Richard S. Ellis, N. M. Forster Schreiber, Tucker Jones, Ali Ahmad Khostovan, Derek J. McLeod, Ross J. McLure, Desika Narayanan, Pascal Oesch, Anthony J. Pahl

Abstract: We probe galactic-scale outflows in star-forming galaxies at $z\gtrsim2.5$ drawn from the \textit{JWST}/NIRSpec AURORA program. For the first time, we directly compare outflow properties from the early universe to the present day using near-UV absorption lines. We measure ISM kinematics from Fe\,{\sc ii} and Mg\,{\sc ii} absorption features in 41 and 43 galaxies, respectively, and examine how thes… ▽ More We probe galactic-scale outflows in star-forming galaxies at $z\gtrsim2.5$ drawn from the \textit{JWST}/NIRSpec AURORA program. For the first time, we directly compare outflow properties from the early universe to the present day using near-UV absorption lines. We measure ISM kinematics from Fe\,{\sc ii} and Mg\,{\sc ii} absorption features in 41 and 43 galaxies, respectively, and examine how these kinematics correlate with galaxy properties. We find that galaxies with outflows tend to have higher stellar masses, and that maximum outflow velocities increase with stellar mass, SFR, UV slope $β$, $E(B-V)$, and $A_V$. We also find that Mg\,{\sc ii} emission is more common in galaxies with lower masses, higher sSFRs, and less dust. These trends are consistent with those in star-forming galaxies at $z<2$ when using the same outflow tracers, suggesting that the feedback from star formation has played a persistent role in shaping galaxy evolution over cosmic time. We also directly compare near-UV and far-UV features in the same NIRSpec spectrum for a $z=5.19$ galaxy, finding consistent ISM kinematics and demonstrating that different tracers yield comparable measurements. We also detect Na\,D absorption in 10 galaxies, which have higher stellar mass, SFR, and dust attenuation compared to galaxies without Na\,D absorption, which is consistent with $z\sim0$ studies. The broad continuum coverage and sensitivity of NIRSpec will enable future studies with larger samples, allowing for robust tests of these trends across a wider dynamic range of galaxy properties. △ Less

Submitted 22 January, 2026; v1 submitted 20 June, 2025; originally announced June 2025.

Comments: 22 pages, 10 figures, 3 tables, accepted to ApJ

NEXUS: A Spectroscopic Census of Broad-line AGNs and Little Red Dots at $3\lesssim z\lesssim 6$

Authors: Ming-Yang Zhuang, Junyao Li, Yue Shen, Xiaojing Lin, Alice E. Shapley, Feige Wang, Qiaoya Wu, Qian Yang

Abstract: We present a spectroscopic sample of 23 broad-line AGNs (BLAGNs) at $3\lesssim z\lesssim 6$ selected using F322W2+F444W NIRCam/WFSS grism spectroscopy of the central 100 ${\rm arcmin^2}$ 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… ▽ More We present a spectroscopic sample of 23 broad-line AGNs (BLAGNs) at $3\lesssim z\lesssim 6$ selected using F322W2+F444W NIRCam/WFSS grism spectroscopy of the central 100 ${\rm arcmin^2}$ 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 $\sim 10^{-5}\,{\rm cMpc^{-3}}$, with a hint of declining towards the lower end of the probed redshift range. These BLAGNs and LRDs span broad H$α$ luminosities of $\sim 10^{42.2}-10^{43.7}\,{\rm erg\,s^{-1}}$, black hole masses of $\sim 10^{6.3}-10^{8.4}\,M_\odot$, and Eddington ratios of $\sim 0.1-1$ (median value 0.4), though the black hole mass and Eddington ratio estimates 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 parsec) 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. This host emission largely accounts for the peculiar UV upturn of the LRD spectral energy distribution. We also measure the small-scale ($\lesssim 1\,{\rm cMpc}$) 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 $3.30_{-2.04}^{+2.88}$ and typical halo masses of a few $\times 10^{11}\,h^{-1}M_\odot$ for BLAGNs at the sample median redshift of $z\sim 4.5$. However, the inferred linear bias and halo masses of LRDs, while formally consistent with those for BLAGNs at $\sim 1.5σ$, appear too large to be compatible with their space density, suggesting LRDs may have strong excess clustering on small scales. △ Less

Submitted 26 May, 2025; originally announced May 2025.

Comments: 26 pages, 17 figures, 4 tables. Submitted to ApJ

Stacking PANCAKEZ: sPectroscopic Analysis with NirspeC stAcKs in the Epoch of reioniZation. Weak ISM Absorption and Implications for Ionizing Photon Escape at $z\sim7$

Authors: Kelsey S. Glazer, Tucker Jones, Yuguang Chen, Ryan L. Sanders, Marusa Bradac, Anthony J. Pahl, Alice E. Shapley, Richard S. Ellis, Michael W. Topping, Naveen A. Reddy

Abstract: We present a spectral stacking analysis of galaxies at $z\geq6$ observed with the James Webb Space Telescope (JWST). We curate a sample of $64$ galaxies spanning redshifts $z_{\rm spec} = 6.0 - 9.4$ which have NIRSpec medium resolution data. The stacks achieve sufficient signal-to-noise to measure equivalent widths (EW) and velocity centroids ($v_{\rm{cen}}$) of low-ionization species (LIS) absorp… ▽ More We present a spectral stacking analysis of galaxies at $z\geq6$ observed with the James Webb Space Telescope (JWST). We curate a sample of $64$ galaxies spanning redshifts $z_{\rm spec} = 6.0 - 9.4$ which have NIRSpec medium resolution data. The stacks achieve sufficient signal-to-noise to measure equivalent widths (EW) and velocity centroids ($v_{\rm{cen}}$) of low-ionization species (LIS) absorption features, transmitted Lyman-alpha ($\rm{Lyα}$) emission, and nebular emission lines. Overall, we find our sample has weaker LIS absorption lines ($\rm{EW}(\rm{LIS}) \approx 1 Å$), smaller $v_{\rm{cen,LIS}} \approx -20 \pm 50~ \rm{km} \; \rm{s}^{-1}$, and significantly suppressed $\rm{Lyα}$ emission ($\rm{EW}(\rm{Lyα}) \approx 5~Å$), compared to similar studies undertaken at lower redshift. The weaker LIS absorption may suggest a lower covering fraction of HI and larger escape fraction of ionizing photons from our sample. Additionally, the smaller blueshifted $v_{\rm{cen,LIS}}$ indicates less prevalent or weaker outflows in $z>6$ galaxies. Stacking our sub-sample of $\rm{Lyα}$ emitters (LAEs), we find high EW$(\rm{H}β) \approx 170 \pm 4~Å$ and a detection of nebular $\rm{C}\; \rm{IV}$ emission suggesting higher $ξ_{ion}$ in LAEs at $z>6$. This work showcases the enormous potential for stacked JWST spectra revealing properties of galaxies and their diffuse interstellar medium in the epoch of reionization. △ Less

Submitted 29 April, 2025; originally announced April 2025.

Comments: 23 pages, 13 figures, 5 tables

No [CII] or dust detection in two Little Red Dots at z$_{\rm spec}$ > 7

Authors: Mengyuan Xiao, Pascal A. Oesch, Longji Bing, David Elbaz, Jorryt Matthee, Yoshinobu Fudamoto, Seiji Fujimoto, Rui Marques-Chaves, Christina C. Williams, Miroslava Dessauges-Zavadsky, Francesco Valentino, Gabriel Brammer, Alba Covelo-Paz, Emanuele Daddi, Johan P. U. Fynbo, Steven Gillman, Michele Ginolfi, Emma Giovinazzo, Jenny E. Greene, Qiusheng Gu, Garth Illingworth, Kohei Inayoshi, Vasily Kokorev, Romain A. Meyer, Rohan P. Naidu , et al. (8 additional authors not shown)

Abstract: Little Red Dots (LRDs) are compact, point-like sources characterized by their red color and broad Balmer lines, which have been debated to be either dominated by active galactic nuclei (AGN) or dusty star-forming galaxies (DSFGs). Here we report two LRDs (ID9094 and ID2756) at z$_{\rm spec}$>7, recently discovered in the JWST FRESCO GOODS-North field. Both satisfy the "v-shape" colors and compactn… ▽ More Little Red Dots (LRDs) are compact, point-like sources characterized by their red color and broad Balmer lines, which have been debated to be either dominated by active galactic nuclei (AGN) or dusty star-forming galaxies (DSFGs). Here we report two LRDs (ID9094 and ID2756) at z$_{\rm spec}$>7, recently discovered in the JWST FRESCO GOODS-North field. Both satisfy the "v-shape" colors and compactness criteria for LRDs and are identified as Type-I AGN candidates based on their broad H$β$ emission lines (full width at half maximum: 2280$\pm$490 km/s for ID9094 and 1070$\pm$240 km/s for ID2756) and narrow [OI] lines ($\sim$ 300-400 km/s). To investigate their nature, we conduct deep NOEMA follow-up observations targeting the [CII] 158${\rm μm}$ emission line and the 1.3 mm dust continuum. We do not detect [CII] or 1.3 mm continuum emission for either source. Notably, in the scenario that the two LRDs were DSFGs, we would expect significant detections: $>16σ$ for [CII] and $>3σ$ for the 1.3 mm continuum of ID9094, and $>5σ$ for [CII] of ID2756. Using the 3$σ$ upper limits of [CII] and 1.3 mm, we perform two analyses: (1) UV-to-FIR spectral energy distribution (SED) fitting with and without AGN components, and (2) comparison of their properties with the L$_{[CII]}$-SFR$_{tot}$ empirical relation. Both analyses are consistent with a scenario where AGN activity may contribute to the observed properties, though a dusty star-forming origin cannot be fully ruled out. Our results highlight the importance of far-infrared observations for studying LRDs, a regime that remains largely unexplored. △ Less

Submitted 2 July, 2025; v1 submitted 3 March, 2025; originally announced March 2025.

Comments: 12 pages, 5 main figures, 1 extended figure, 3 tables; accepted by A&A

Journal ref: A&A 700, A231 (2025)

The JWST EXCELS survey: Probing strong-line diagnostics and the chemical evolution of galaxies over cosmic time using Te-metallicities

Authors: D. Scholte, F. Cullen, A. C. Carnall, K. Z. Arellano-Córdova, T. M. Stanton, L. Barrufet, C. T. Donnan, J. S. Dunlop, H. -H. Leung, D. J. McLeod, R. J. McLure, J. M. Moustakas, C. L. Pollock, A. E. Shapley, S. Stevenson, H. Zou

Abstract: We present an analysis of the rest-frame optical spectra of 22 [OIII]$λ$4363 detected galaxies in the redshift range $1.65 < z < 7.92$ (with $\langle z \rangle$ = 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 [OIII]$λ$4363 detected galaxies from the DESI Early Data Release… ▽ More We present an analysis of the rest-frame optical spectra of 22 [OIII]$λ$4363 detected galaxies in the redshift range $1.65 < z < 7.92$ (with $\langle z \rangle$ = 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 [OIII]$λ$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 $\widehat{R}$ 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, $\widehat{RNe}$, which can be used to robustly estimate metallicities when the [OIII]$λ$5007 is redshifted out of the wavelength range of JWST/NIRSpec at $z > 9.5$. We also show that strong-line diagnostics using the [NII]$λ$6584 emission line are likely to be biased at high-redshift due to a moderate enhancement in the average N/O abundance ratios (at fixed O/H) in these sources. Finally, we discuss the location of our new [OIII]$λ$4363 detected galaxies at $z \simeq 4$ 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 fundamental metallicity relation. △ Less

Submitted 14 February, 2025; originally announced February 2025.

Comments: 27 pages, 15 figures. Submitted to MNRAS

The AURORA Survey: The Evolution of Multi-phase Electron Densities at High Redshift

Authors: Michael W. Topping, Ryan L. Sanders, Alice E. Shapley, Anthony J. Pahl, Naveen A. Reddy, Daniel P. Stark, Danielle A. Berg, Leonardo Clarke, Fergus Cullen, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, Garth D. Illingworth, Tucker Jones, Desika Narayanan, Max Pettini, Daniel Schaerer

Abstract: We present an analysis of deep $\textit{JWST}$/NIRSpec spectra of star-forming galaxies at $z\simeq1.4-10$, observed as part of the AURORA survey. We infer median low-ionization electron densities of $268_{-49}^{+45}~\rm cm^{-3}$, $350_{-76}^{+140}~\rm cm^{-3}$, and $480_{-310}^{+390}~\rm cm^{-3}$ at redshifts z$=2.3$, $z=3.2$, and $z=5.3$, respectively, revealing an evolutionary trend following… ▽ More We present an analysis of deep $\textit{JWST}$/NIRSpec spectra of star-forming galaxies at $z\simeq1.4-10$, observed as part of the AURORA survey. We infer median low-ionization electron densities of $268_{-49}^{+45}~\rm cm^{-3}$, $350_{-76}^{+140}~\rm cm^{-3}$, and $480_{-310}^{+390}~\rm cm^{-3}$ at redshifts z$=2.3$, $z=3.2$, and $z=5.3$, respectively, revealing an evolutionary trend following $(1+z)^{1.5\pm0.6}$. 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 $\rm [NeIII]\lambda3869/[OII]\lambda3727$ and, potentially, $\rm [OIII]\lambda5007/[OII]\lambda3727$, although variations in dust attenuation complicate the latter. Additionally, electron density is more strongly correlated with distance from the local BPT sequence than can be explained by simple photoionization models. We further derive electron densities from the CIII] doublet probing higher-ionization gas, and find a median value of $1.4_{-0.5}^{+0.7}\times10^4~\rm cm^{-3}$, $\sim30$ times higher than densities inferred from [SII]. 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. △ Less

Submitted 12 February, 2025; originally announced February 2025.

Comments: 16 pages, 8 figures; submitted

The JWST EXCELS survey: an extremely metal-poor galaxy at $z=8.271$ hosting an unusual population of massive stars

Authors: F. Cullen, A. C. Carnall, D. Scholte, D. J. McLeod, R. J. McLure, K. Z. Arellano-Córdova, T. M Stanton, C. T. Donnan, J. S. Dunlop, A. E. Shapley, L. Barrufet, R. Begley, C. Bondestam, M. Cirasuolo, H. -H. Leung, C. L. Pollock, S. Stevenson

Abstract: We present an analysis of the rest-frame optical ($λ\simeq 3100-5600 \,$Å) spectrum of a $\mathrm{log}_{10}(M_*/\mathrm{M_\odot}) = 8.6$ star-forming galaxy at $z=8.271$ from JWST/NIRSpec medium-resolution observations taken as part of the EXCELS survey. The galaxy (EXCELS-63107) is compact, with a size consistent with the size of local star-forming cluster complexes ($r_e < 200 \, \rm{pc}$) and h… ▽ More We present an analysis of the rest-frame optical ($λ\simeq 3100-5600 \,$Å) spectrum of a $\mathrm{log}_{10}(M_*/\mathrm{M_\odot}) = 8.6$ star-forming galaxy at $z=8.271$ from JWST/NIRSpec medium-resolution observations taken as part of the EXCELS survey. The galaxy (EXCELS-63107) is compact, with a size consistent with the size of local star-forming cluster complexes ($r_e < 200 \, \rm{pc}$) and has an extremely steep UV continuum measured from JWST/NIRCam photometry ($β=-3.3\pm0.3$). The JWST/NIRSpec G395M spectrum of EXCELS-63107 is notable for its strong [OIII]$\lambda4363$ auroral-line emission relative to the [OIII]$\lambda5007$ forbidden line. Via a detailed emission-line and photoionization-modelling analysis, we find that the the observed properties of EXCELS-63107 are consistent with the presence of an ionizing source with an effective temperature of $T_{\rm eff} \gtrsim 80 \, 000\,\rm{K}$ heating ionized gas with a density of $n_e < 10^4 \, \rm{cm}^{-3}$ to a volume-averaged electron temperature of $T_e \simeq 34 \, 000\,\rm{K}$. Crucially, we find that stellar population models assuming a standard IMF are not capable of producing the required heating. We determine an oxygen abundance of ${12+\mathrm{log(O/H)}= 6.89^{+0.26}_{-0.21}}$ which is one of the lowest directly constrained oxygen abundances measured in any galaxy to date, and $\simeq 10 \times$ lower than is typical for $z\simeq8$ 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 $\simeq 10-30 \, \times$ excess of $M > 50 \, \rm{M}_{\odot}$ 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. △ Less

Submitted 2 June, 2025; v1 submitted 19 January, 2025; originally announced January 2025.

Comments: 18 pages, 11 figures, updated to the final MNRAS accepted version

The JWST EXCELS survey: direct estimates of C, N, and O abundances in two relatively metal-rich galaxies at $\mathbf{z\simeq5}$

Authors: K. Z. Arellano-Córdova, F. Cullen, A. C. Carnall, D. Scholte, T. M. Stanton, C. Kobayashi, Z. Martinez, D. A. Berg, L. Barrufet, R. Begley, C. T. Donnan, J. S. Dunlop, M. L. Hamadouche, D. J. McLeod, R. J. McLure, K. Rowlands, A. E. Shapley

Abstract: We present a spectroscopic analysis of two star-forming galaxies at $z\simeq5$ observed with JWST/NIRSpec as part of the EXCELS survey. The detection of the CIII]~$λλ$1906,09, [OII] $λλ$3726,29, [OIII] $λλ$4363,5007, and [NII] $λ$6584 emission lines enables an investigation of the $\mathrm{C/O}$, $\mathrm{N/O}$, and $\mathrm{C/N}$ abundance ratios using the temperature-sensitive method. The galaxi… ▽ More We present a spectroscopic analysis of two star-forming galaxies at $z\simeq5$ observed with JWST/NIRSpec as part of the EXCELS survey. The detection of the CIII]~$λλ$1906,09, [OII] $λλ$3726,29, [OIII] $λλ$4363,5007, and [NII] $λ$6584 emission lines enables an investigation of the $\mathrm{C/O}$, $\mathrm{N/O}$, and $\mathrm{C/N}$ abundance ratios using the temperature-sensitive method. The galaxies have stellar masses of ${\mathrm{log}(M_{\star}/\mathrm{M}_{\odot}) = 8.09^{+\, 0.24}_{-0.15}}$ and ${\mathrm{log}(M_{\star}/\mathrm{M}_{\odot}) = 8.02^{+\, 0.06}_{-0.08}}$ with metallicities of $Z \simeq 0.2 \, \rm{Z_{\odot}}$ and $Z \simeq 0.3 \, \rm{Z_{\odot}}$. These metallicities are somewhat higher than is typical for other $z\gtrsim 5$ galaxies with similar stellar mass and are comparable to $z \simeq 0$ analogues. Both galaxies display evidence for elevated N/O ratios with respect to the typical star-forming galaxies at $z\simeq0$, with ${\mathrm{log(N/O)} = -1.07^{+\,0.17}_{-0.13}}$ and ${\mathrm{log(N/O)} = -0.86^{+\,0.15}_{-0.11}}$ respectively. In contrast, we find low C abundances, with ${\mathrm{log(C/O)}=-0.82\pm0.22}$ and ${\mathrm{log(C/O)}=-1.02\pm0.22}$, consistent with the predicted yields of core-collapse supernovae. Following the trend observed in other high-redshift sources, we find that the $\mathrm{C/N}$ ratios are lower at fixed $\mathrm{O/H}$ compared to the majority of local galaxies. Via a comparison to detailed chemical evolution models, we find that a standard or bottom-heavy IMF can explain the observed abundance ratios where the N-enrichment comes from intermediate mass ($\simeq 4-7 \, \mathrm{M}_{\odot}$) stars. Our results demonstrate that robust measurements of CNO abundances with \emph{JWST} can reveal unique enrichment pathways in galaxies as a function of both metallicity and redshift. △ Less

Submitted 22 May, 2025; v1 submitted 13 December, 2024; originally announced December 2024.

Comments: 17 pages, 8 Figures, and 3 Tables. Accepted in MNRAS

The JWST EXCELS survey: tracing the chemical enrichment pathways of high-redshift star-forming galaxies with O, Ar and Ne abundances

Authors: T. M. Stanton, F. Cullen, A. C. Carnall, D. Scholte, K. Z. Arellano-Córdova, D. J. McLeod, R. Begley, C. T. Donnan, J. S. Dunlop, M. L. Hamadouche, R. J. McLure, A. E. Shapley, C. Bondestam, S. Stevenson

Abstract: We present an analysis of eight star-forming galaxies with $\langle z \rangle = 4.0$ from the JWST EXCELS survey for which we obtain robust chemical abundance estimates for the $α$-elements O, Ne and Ar. The $α$-elements are primarily produced via core-collapse supernovae (CCSNe) which should result in $α$-element abundance ratios that do not vary significantly across cosmic time. However, Type Ia… ▽ More We present an analysis of eight star-forming galaxies with $\langle z \rangle = 4.0$ from the JWST EXCELS survey for which we obtain robust chemical abundance estimates for the $α$-elements O, Ne and Ar. The $α$-elements are primarily produced via core-collapse supernovae (CCSNe) which should result in $α$-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 ${\rm Ar/O}$ at $z > 2$, and we find that our sample exhibits sub-solar Ar/O ratios on average, with $\rm{Ar/O} = 0.65 \pm 0.10 \, (\rm{Ar/O})_{\odot}$. In contrast, the average Ne/O abundance is fully consistent with the solar ratio, with $\rm{Ne/O} = 1.07 \pm 0.12 \, (\rm{Ne/O})_{\odot}$. 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. △ Less

Submitted 22 January, 2025; v1 submitted 18 November, 2024; originally announced November 2024.

Comments: 14 pages, 9 figures. Accepted for publication in MNRAS

NEXUS Early Data Release: NIRCam Imaging and WFSS Spectroscopy from the First (Partial) Wide Epoch

Authors: Ming-Yang Zhuang, Feige Wang, Fengwu Sun, Yue Shen, Junyao Li, Adam J. Burgasser, Xiaohui Fan, Jenny E. Greene, Gautham Narayan, Alice E. Shapley, Qian Yang

Abstract: We present the Early Data Release of the Multi-Cycle JWST-NEXUS Treasury program (2024-2028), which includes NIRCam imaging and WFSS observations from the first (partial) NEXUS-Wide epoch covering the central 100 ${\rm arcmin^2}$ of the NEXUS field, located near the North Ecliptic Pole and within the Euclid Ultra-Deep Field. We release reduced NIRCam mosaics (F090W, F115W, F150W, F200W, F356W, F44… ▽ More We present the Early Data Release of the Multi-Cycle JWST-NEXUS Treasury program (2024-2028), which includes NIRCam imaging and WFSS observations from the first (partial) NEXUS-Wide epoch covering the central 100 ${\rm arcmin^2}$ of the NEXUS field, located near the North Ecliptic Pole and within the Euclid Ultra-Deep Field. We release reduced NIRCam mosaics (F090W, F115W, F150W, F200W, F356W, F444W), photometric source catalogs, as well as preliminary WFSS spectra (in F322W2 and F444W) for the subset of bright sources (F356W$<$21 mag or F444W$<$21 mag). These observations fully cover the NEXUS-Deep area, and anchor the long-term baseline of the program. These data will be used for initial target selection for the NIRSpec/MSA spectroscopy starting from June 2025. The NIRCam imaging reaches depths of 27.4--28.2 (AB) mags in F090W--F444W. Upcoming NEXUS-Wide epochs will expand the area to the full $\sim 400\,{\rm arcmin^2}$, and improve the NIRCam exposure depths in the Wide tier by a factor of three. In addition, this central region will be repeatedly covered by the NEXUS-Deep observations (NIRCam imaging and NIRSpec/MSA PRISM spectroscopy) over 18 epochs with a $\sim 2$-month cadence. We demonstrate the data quality of the first NEXUS observations, and showcase some example science cases enabled by these data. △ Less

Submitted 10 November, 2024; originally announced November 2024.

Comments: 14 pages, 9 figures, 2 tables. Data products are publicly accessible at https://ariel.astro.illinois.edu/nexus/edr/ Online interactive map for quick visualization of released images and WFSS spectra can be found at https://ariel.astro.illinois.edu/nexus/map/

The evolution of [OIII]$+\rm{H}β$ equivalent width from $\mathbf{z\simeq3-8}$: implications for the production and escape of ionizing photons during reionization

Authors: R. Begley, R. J. McLure, F. Cullen, D. J. McLeod, J. S. Dunlop, A. C. Carnall, T. M. Stanton, A. E. Shapley, R. Cochrane, C. T. Donnan, R. S. Ellis, A. Fontana, N. A. Grogin, A. M. Koekemoer

Abstract: Accurately quantifying the ionizing photon production efficiency ($ξ_\rm{ion}$) of $z>6$ star-forming galaxies (SFGs) is necessary to understand their contribution to reionization. We investigate the ionizing properties of N=279 SFGs selected at $z=6.9-7.6$ from the JWST Cycle-1 imaging programmes; PRIMER and JADES. We use BAGPIPES to consistently infer the equivalent widths of their [OIII]+… ▽ More Accurately quantifying the ionizing photon production efficiency ($ξ_\rm{ion}$) of $z>6$ star-forming galaxies (SFGs) is necessary to understand their contribution to reionization. We investigate the ionizing properties of N=279 SFGs selected at $z=6.9-7.6$ from the JWST Cycle-1 imaging programmes; PRIMER and JADES. We use BAGPIPES to consistently infer the equivalent widths of their [OIII]+$\rm{Hβ}$ emission lines ($W_λ$) and their physical properties. To supplement our high-redshift galaxies, we measure $W_λ$ photometrically for a sample of N=253 $z=3.2-3.6$ SFGs selected from the VANDELS spectroscopic survey. Comparing these samples, we find a strong apparent redshift evolution in their median $W_λ$, increasing from $W_λ=310\pm25\,Å$ in VANDELS to $W_λ=540\pm25\,Å$ in our JWST-based sample. In the JWST sample at $z>7$, we find that $W_λ$ correlates with both stellar mass and UV luminosity, with high-mass, $M_{ UV}-$faint galaxies producing systematically weaker emission lines. Moreover, we discover a departure from the standard log-normal shape of the $W_λ$ distribution, characterised by a more pronounced tail at lower $W_λ$, consistent with increasingly bursty star formation. Using $W_λ$ as a proxy for $ξ_\rm{ion}$, and UV spectral slope as a proxy for LyC escape fraction ($f_\rm{esc}$), we find a minority of galaxies with high $ξ_\rm{ion}$ and $f_\rm{esc}$ (e.g., $\rm{log(ξ_{ion}/erg^{-1}Hz})\sim25.6$ and $f_\rm{esc}\sim0.15$). However, we find that the LyC photon budget at $z>7$ is dominated by galaxies with more moderate output, close to the sample median of $\rm{log(ξ_{ion}/erg^{-1}Hz})\sim25.3$ and $f_\rm{esc}\sim0.05$. This is consistent with estimates for the number of LyC photons required to power reionization at $z>7$, with no evidence for over or under-production. △ Less

Submitted 3 February, 2025; v1 submitted 14 October, 2024; originally announced October 2024.

Comments: 18 pages, 9 figures + 1 appendix. Accepted to MNRAS

The AURORA Survey: An Extraordinarily Mature, Star-forming Galaxy at $z\sim 7$

Authors: Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Naveen A. Reddy, Anthony J. Pahl, Pascal A. Oesch, Danielle A. Berg, Rychard J. Bouwens, Gabriel Brammer, Adam C. Carnall, Fergus Cullen, Romeel Davé, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, Steven R . Furlanetto, Karl Glazebrook, Garth D. Illingworth, Tucker Jones, Mariska Kriek, Derek J. McLeod, Ross J. McLure, Desika Narayanan, Max Pettini, Daniel Schaerer , et al. (6 additional authors not shown)

Abstract: 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 AURORA survey, and is also covered by public multi-wavelength HST and JWST imaging. While the large stellar mass of GOODSN-100182 (~10^10 M_sun) was indicated prior to JWST, NIRCam rest-optical imaging now reveals the presence of an exten… ▽ More 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 AURORA survey, and is also covered by public multi-wavelength HST and JWST imaging. While the large stellar mass of GOODSN-100182 (~10^10 M_sun) was indicated prior to JWST, NIRCam rest-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-optical nebular emission lines ranging in wavelength from [OII]3727 up to [NII]6583. The ratios of Balmer lines suggest significant dust attenuation (E(B-V)_gas=0.40+0.10/-0.09), consistent with the red rest-UV slope inferred for GOODSN-100182 (beta=-0.50+/-0.09). The star-formation rate based on dust-corrected H-alpha emission is log(SFR(H-alpha)/ M_sun/yr)=2.02+0.13/-0.14, well above the z~7 star-forming main sequence in terms of specific SFR. Strikingly, the ratio of [NII]6583/H-alpha emission suggests almost solar metallicity, as does the ratio ([OIII]5007/H-beta)/([NII]6583/H-alpha) and the detection of the faint [FeII]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. △ Less

Submitted 31 January, 2025; v1 submitted 30 September, 2024; originally announced October 2024.

Comments: 16 pages, 13 figures, accepted to ApJ

Stacking and Analyzing $z\approx 2$ MOSDEF Galaxies by Spectral Types: Implications for Dust Geometry and Galaxy Evolution

Authors: Brian Lorenz, Mariska Kriek, Alice E. Shapley, Ryan L. Sanders, Alison L. Coil, Joel Leja, Bahram Mobasher, Erica Nelson, Sedona H. Price, Naveen A. Reddy, Jordan N. Runco, Katherine A. Suess, Irene Shivaei, Brian Siana, Daniel R. Weisz

Abstract: We examine star-formation and dust properties for a sample of 660 galaxies at $1.37\leq z\leq 2.61$ in the MOSDEF survey by dividing them into groups with similarly-shaped spectral energy distributions (SEDs). For each group, we combine the galaxy photometry into a finely-sampled composite SED, and stack their spectra. This method enables the study of more complete galaxy samples, including galaxi… ▽ More We examine star-formation and dust properties for a sample of 660 galaxies at $1.37\leq z\leq 2.61$ in the MOSDEF survey by dividing them into groups with similarly-shaped spectral energy distributions (SEDs). For each group, we combine the galaxy photometry into a finely-sampled composite SED, and stack their spectra. This method enables the study of more complete galaxy samples, including galaxies with very faint emission lines. We fit these composite SEDs with Prospector to measure the stellar attenuation and SED-based star-formation rates (SFRs). We also derive emission-line properties from the spectral stacks, including Balmer decrements, dust-corrected SFRs, and metallicities. We find that stellar attenuation correlates most strongly with mass, while nebular attenuation correlates strongly with both mass and SFR. Furthermore, the excess of nebular compared to stellar attenuation correlates most strongly with SFR. The highest SFR group has 2 mag of excess nebular attenuation. Our results are consistent with a model in which star-forming regions become more dusty as galaxy mass increases. To explain the increasing excess nebular attenuation, we require a progressively larger fraction of star formation to occur in highly-obscured regions with increasing SFR. This highly-obscured star formation could occur in dusty clumps or central starbursts. Additionally, as each galaxy group represents a different evolutionary stage, we study their locations on the UVJ and SFR-mass diagrams. As mass increases, metallicity and dust attenuation increase, while sSFR decreases. However, the most massive group moves towards the quiescent region of the UVJ diagram, while showing less obscuration, potentially indicating removal of dust. △ Less

Submitted 26 September, 2024; originally announced September 2024.

Comments: 21 pages, 7 figures, accepted for publication in ApJ

NEXUS: the North ecliptic pole EXtragalactic Unified Survey

Authors: Yue Shen, Ming-Yang Zhuang, Junyao Li, Adam J. Burgasser, Xiaohui Fan, Jenny E. Greene, Gautham Narayan, Alice E. Shapley, Fengwu Sun, Feige Wang, Qian Yang

Abstract: NEXUS is a JWST Multi-Cycle (Cycles 3-5; 368 primary hrs) GO Treasury imaging and spectroscopic survey around the North Ecliptic Pole. It contains two overlapping tiers. The Wide tier ($\sim 400~{\rm arcmin}^2$) performs NIRCam/WFSS 2.4-5 micron grism spectroscopy with three epochs over 3 years (final continuum ${\rm S/N/pixel>3}$ at F444W$<22.2$). The Deep tier ($\sim 50~{\rm arcmin}^2$) performs… ▽ More NEXUS is a JWST Multi-Cycle (Cycles 3-5; 368 primary hrs) GO Treasury imaging and spectroscopic survey around the North Ecliptic Pole. It contains two overlapping tiers. The Wide tier ($\sim 400~{\rm arcmin}^2$) performs NIRCam/WFSS 2.4-5 micron grism spectroscopy with three epochs over 3 years (final continuum ${\rm S/N/pixel>3}$ at F444W$<22.2$). The Deep tier ($\sim 50~{\rm arcmin}^2$) performs high-multiplexing NIRSpec 0.6-5.3 micron MOS/PRISM spectroscopy for $\sim 10,000$ targets, over 18 epochs with a 2-month cadence (epoch/final continuum ${\rm S/N/pixel>3}$ at F200W$\lesssim 27/29$). All epochs have simultaneous multi-band NIRCam and MIRI imaging ($5σ$ final depths of $\sim 28-29$ in NIRCam and $\sim 25$ in MIRI). The field is within the continuous viewing zone of JWST, and is fully covered by the Euclid Ultra-Deep Field, with 0.9-2 micron deep Euclid spectroscopy and cadenced photometry. NEXUS has three science pillars. First, with its massive and nearly complete (flux-limited) spectroscopic samples and deep photometry, it will perform efficient classification and physical characterization of galaxies and AGNs from $z\sim 1$ to Cosmic Dawn. With the large contiguous area coverage, it will measure the spatial clustering and demography of the first galaxies and SMBHs at $z>6$. Second, multi-epoch observations enable systematic time-domain investigations, focusing on $z>3$ transients and low-mass AGN reverberation mapping. Third, the comprehensive data set will enable knowledge transfer to other legacy fields, create data challenges, and initiate benchmark work for future space missions. With rapid public releases of processed data and an open invitation for collaboration, NEXUS aims for broad and swift community engagement, to become a powerhouse to drive transformative advancements in multiple key science areas of astronomy. △ Less

Submitted 22 August, 2024; originally announced August 2024.

Comments: 19 pages

MSA-3D: dissecting galaxies at z~1 with high spatial and spectral resolution

Authors: Ivana Barišić, Tucker Jones, Kris Mortensen, Themiya Nanayakkara, Yuguang Chen, Ryan Sanders, James S. Bullock, Kevin Bundy, Claude-André Faucher-Giguère, Karl Glazebrook, Alaina Henry, Mengting Ju, Matthew Malkan, Takahiro Morishita, Danail Obreschkow, Namrata Roy, Juan M. Espejo Salcedo, Alice E. Shapley, Tommaso Treu, Xin Wang, Kyle B. Westfall

Abstract: 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 $0.5 \lesssim z \lesssim 1.5$, correspondin… ▽ More 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 $0.5 \lesssim z \lesssim 1.5$, corresponding to the epoch when spiral thin-disk galaxies of the modern Hubble sequence are thought to emerge, obtaining kpc-scale maps of rest-frame optical nebular emission lines with spectral resolution $R\simeq2700$. 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 $M_{*} = 10^{10.3}~M_{\odot}$, star formation rate~$=3~M_{\odot}$ yr$^{-1}$) with prominent face-on spiral structure. We show that the galaxy exhibits a rotationally supported disk with moderate velocity dispersion ($σ= 36^{+5}_{-4}$~\kms), a negative radial metallicity gradient ($-0.020\pm0.002$~dex\,kpc$^{-1}$), a dust attenuation gradient, and an exponential star formation rate density profile which closely matches the stellar continuum. These properties are characteristic of local spirals, indicating that mature galaxies are in place at $z\sim1$. We also describe the customized data reduction and original cube-building software pipelines which 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 $z\sim0.1$ universe. △ Less

Submitted 10 October, 2024; v1 submitted 15 August, 2024; originally announced August 2024.

Comments: 24 pages, 12 figures, 1 table; submitted to ApJ, comments welcome. Our custom designed data reduction pipeline (MSA3D) and example processed data-cube will be publicly released before the JWST Cycle 4 deadline. MSA3D package on GitHub: https://github.com/barisiciv/msa3d.git

The AURORA Survey: The Nebular Attenuation Curve of a Galaxy at z=4.41 from Ultraviolet to Near-Infrared Wavelengths

Authors: Ryan L. Sanders, Alice E. Shapley, Michael W. Topping, Naveen A. Reddy, Danielle A. Berg, Rychard J. Bouwens, Gabriel Brammer, Adam C. Carnall, Fergus Cullen, Romeel Davé, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, Steven R. Furlanetto, Karl Glazebrook, Garth D. Illingworth, Tucker Jones, Mariska Kriek, Derek J. McLeod, Ross J. McLure, Desika Narayanan, Pascal A. Oesch, Anthony J. Pahl, Max Pettini, Daniel Schaerer , et al. (6 additional authors not shown)

Abstract: We use JWST/NIRSpec observations from the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey to constrain the shape of the nebular attenuation curve of a star-forming galaxy at z=4.41, GOODSN-17940. We utilize 11 unblended HI recombination lines to derive the attenuation curve spanning optical to near-infrared wavelengths (3751-9550 Å). We then leverage a high-S… ▽ More We use JWST/NIRSpec observations from the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey to constrain the shape of the nebular attenuation curve of a star-forming galaxy at z=4.41, GOODSN-17940. We utilize 11 unblended HI recombination lines to derive the attenuation curve spanning optical to near-infrared wavelengths (3751-9550 Å). We then leverage a high-S/N 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 the same attenuation as 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. △ Less

Submitted 19 May, 2026; v1 submitted 9 August, 2024; originally announced August 2024.

Comments: 24 pages, 7 figures, 1 table, accepted to ApJ

A spectroscopic analysis of the ionizing photon production efficiency in JADES and CEERS: implications for the ionizing photon budget

Authors: Anthony J. Pahl, Michael W. Topping, Alice Shapley, Ryan Sanders, Naveen A. Reddy, Leonardo Clarke, Emily Kehoe, Trinity Bento, Gabe Brammer

Abstract: We have used a combined sample of JADES and CEERS objects in order to constrain ionizing photon production efficiency ($ξ_{\rm ion}$) from JWST/NIRSpec and JWST/NIRCam data. We examine 163 objects at 1.06 < z < 6.71 with significant (3$σ$) spectroscopic detections of H$α$ and H$β$ in order to constrain intrinsic H$α$ luminosities corrected from nebular dust attenuation via Balmer decrements. We co… ▽ More We have used a combined sample of JADES and CEERS objects in order to constrain ionizing photon production efficiency ($ξ_{\rm ion}$) from JWST/NIRSpec and JWST/NIRCam data. We examine 163 objects at 1.06 < z < 6.71 with significant (3$σ$) spectroscopic detections of H$α$ and H$β$ in order to constrain intrinsic H$α$ luminosities corrected from nebular dust attenuation via Balmer decrements. We constrain dust-corrected UV luminosities from best-fit spectral-energy distribution modeling. We find a sample median log$_{10}$($ξ{\rm ion,0}$/erg Hz$^{-1}$) = $25.29^{+0.29}_{-0.37}$, assuming f$_{\rm esc}$=0 for the escape fraction of Lyman continuum emission. We find significant correlation between $ξ_{\rm ion,0}$ and z, with 17 objects at z > 4.64 having median log$_{10}$($ξ_{\rm ion,0}$/erg Hz$^{-1}$) = $25.38^{+0.38}){-0.38}$, with those below having log$_{10}$($ξ_{\rm ion,0}$/erg Hz$^{-1}$) = $25.24^{+0.30}_{-0.33}$. We also find significant, positive correlations between $ξ_{\rm ion,0}$ and LUV; Wλ([O iii]); [O iii]λ5007/[O ii]λλ3726, 3729; and inverse correlations with metallicity. In contrast with some previous results, we find no trends between $ξ_{\rm ion,0}$ and stellar mass, stellar dust attenuation, or UV slope. Applying a multivariate fit to $ξ_{\rm ion,0}$, z, and MUV to an empirically-motivated model of reionization, and folding in f$_{\rm esc}$ estimates from direct observations of the Lyman continuum at z ~ 3 from the Keck Lyman Continuum Spectroscopic survey, we find that the number of ionizing photons entering the IGM causes reionization to end at z ~ 5 - 7. △ Less

Submitted 3 July, 2024; originally announced July 2024.

Comments: 17 pages, 8 figures, submitted to ApJ

Carbon and Iron Deficiencies in Quiescent Galaxies at z=1-3 from JWST-SUSPENSE: Implications for the Formation Histories of Massive Galaxies

Authors: Aliza G. Beverage, Martje Slob, Mariska Kriek, Charlie Conroy, Guillermo Barro, Rachel Bezanson, Gabriel Brammer, Chloe M. Cheng, Anna de Graaff, Natascha M. Förster Schreiber, Marijn Franx, Brian Lorenz, Pavel E. Mancera Piña, Danilo Marchesini, Adam Muzzin, Andrew B. Newman, Sedona H. Price, Alice E. Shapley, Mauro Stefanon, Katherine A. Suess, Pieter van Dokkum, David Weinberg, Daniel R. Weisz

Abstract: We present the stellar metallicities and multi-element abundances (C, Mg, Si, Ca, Ti, Cr, and Fe) of 15 massive (log $M/M_\odot=10.2-11.2$) quiescent galaxies at z=1-3, derived from ultradeep JWST-SUSPENSE spectra. Compared to quiescent galaxies at z~0, these galaxies exhibit a deficiency of 0.26$\pm0.04$ dex in [C/H], 0.16$\pm0.03$ dex in [Fe/H], and 0.07$\pm0.04$ dex in [Mg/H], implying rapid fo… ▽ More We present the stellar metallicities and multi-element abundances (C, Mg, Si, Ca, Ti, Cr, and Fe) of 15 massive (log $M/M_\odot=10.2-11.2$) quiescent galaxies at z=1-3, derived from ultradeep JWST-SUSPENSE spectra. Compared to quiescent galaxies at z~0, these galaxies exhibit a deficiency of 0.26$\pm0.04$ dex in [C/H], 0.16$\pm0.03$ dex in [Fe/H], and 0.07$\pm0.04$ dex in [Mg/H], implying rapid formation and quenching before significant enrichment from asymptotic giant branch stars and Type Ia supernovae. Additionally, we find that galaxies forming at higher redshift consistently show higher [Mg/Fe] and lower [Fe/H] and [Mg/H], regardless of their observed redshift. The evolution in [Fe/H] and [C/H] is therefore primarily driven by lower-redshift samples naturally including galaxies with longer star-formation timescales. In contrast, the lower [Mg/H] likely reflects earlier-forming galaxies expelling larger gas reservoirs during their quenching phase. Consequently, the mass-metallicity relation, primarily reflecting [Mg/H], is somewhat lower at z=1-3 compared to the lower redshift relation. Finally, we compare our results to standard stellar population modeling approaches employing solar abundance patterns and non-parametric star-formation histories (using Prospector). Our SSP-equivalent ages agree with the mass-weighted ages from Prospector, while the metallicities disagree significantly. Nonetheless, the metallicities better reflect [Fe/H] than total [Z/H]. We also find that star-formation timescales inferred from elemental abundances are significantly shorter than those from Prospector, and we discuss the resulting implications for the early formation of massive galaxies. △ Less

Submitted 22 October, 2024; v1 submitted 2 July, 2024; originally announced July 2024.

Comments: Accepted to ApJ; 22 pages, 6 figures, 3 tables

The AURORA Survey: A New Era of Emission-line Diagrams with JWST/NIRSpec

Authors: Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Naveen A. Reddy, Danielle A. Berg, Rychard J. Bouwens, Gabriel Brammer, Adam C. Carnall, Fergus Cullen, Romeel Davé, James S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, Steven R . Furlanetto, Karl Glazebrook, Garth D. Illingworth, Tucker Jones, Mariska Kriek, Derek J. McLeod, Ross J. McLure, Desika Narayanan, Pascal Oesch, Anthony J. Pahl, Max Pettini, Daniel Schaerer , et al. (6 additional authors not shown)

Abstract: 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--5 microns, and medium spectral resolution (R~1000), AURORA includes detections of a large suite of nebular emission lines spanning a broad… ▽ More 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--5 microns, and medium spectral resolution (R~1000), AURORA includes detections of a large suite of nebular emission lines spanning a broad range in rest wavelength. We investigate the locations of AURORA galaxies in multiple different emission-line diagrams, including traditional "BPT" diagrams of [OIII]/Hbeta vs. [NII]/Halpha, [SII]/Halpha, and [OI]/Halpha, and the "ionization-metallicity" diagram of [OIII]/[OII] (O32) vs. ([OIII]+[OII])/Hbeta (R23). We also consider a bluer rest-frame "ionization-metallicity" diagram introduced recently to characterize z>10 galaxies: [NeIII]/[OII] vs. ([NeIII]+[OII])/Hdelta; as well as longer-wavelength diagnostic diagrams extending into the rest-frame near-IR: [OIII]/Hbeta vs. [SIII]/[SII] (S32); and HeI/Pagamma and [SIII]/Pagamma vs. [FeII]/Pabeta. With a significant boost in signal-to-noise and large, representative samples of individual galaxy detections, the AURORA emission-line diagrams presented here definitively confirm a physical picture in which chemically-young, alpha-enhanced, massive stars photoionize the 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 [OIII]/Hbeta vs. [NII]/Halpha 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 [FeII], we must obtain better constraints on dust depletion in the high-redshift ISM. △ Less

Submitted 25 January, 2025; v1 submitted 28 June, 2024; originally announced July 2024.

Comments: 18 pages, 8 figures, accepted to ApJ

The First Combined H$α$ and Rest-UV Spectroscopic Probe of Galactic Outflows at High Redshift

Authors: Emily Kehoe, Alice E. Shapley, N. M Forster Schreiber, Anthony J. Pahl, Michael W. Topping, Naveen A. Reddy, Reinhard Genzel, Sedona H. Price, L. J. Tacconi

Abstract: We investigate the multi-phase structure of gas flows in galaxies. We study 80 galaxies during the epoch of peak star formation ($1.4\leq z\leq2.7$) using data from Keck/LRIS and VLT/KMOS. Our analysis provides a simultaneous probe of outflows using UV emission and absorption features and H$α$ emission. With this unprecedented data set, we examine the properties of gas flows estimated from LRIS an… ▽ More We investigate the multi-phase structure of gas flows in galaxies. We study 80 galaxies during the epoch of peak star formation ($1.4\leq z\leq2.7$) using data from Keck/LRIS and VLT/KMOS. Our analysis provides a simultaneous probe of outflows using UV emission and absorption features and H$α$ emission. With this unprecedented data set, we examine the properties of gas flows estimated from LRIS and KMOS in relation to other galaxy properties, such as star formation rate (SFR), star formation rate surface density ($Σ_{\rm SFR}$), stellar mass (M$_*$), and main sequence offset ($Δ$MS). We find no strong correlations between outflow velocity measured from rest-UV lines centroids and galaxy properties. However, we find that galaxies with detected outflows show higher averages in SFR, $Σ_{\rm SFR}$, and $Δ$MS than those lacking outflow detections, indicating a connection between outflow and galaxy properties. Furthermore, we find a lower average outflow velocity than previously reported, suggesting greater absorption at the systemic redshift of the galaxy. Finally, we detect outflows in 49% of our LRIS sample and 30% in the KMOS sample, and find no significant correlation between outflow detection and inclination. These results may indicate that outflows are not collimated and that H$α$ outflows have a lower covering fraction than low-ionization interstellar absorption lines. Additionally, these tracers may be sensitive to different physical scales of outflow activity. A larger sample size with a wider dynamic range in galaxy properties is needed to further test this picture. △ Less

Submitted 16 September, 2024; v1 submitted 11 June, 2024; originally announced June 2024.

Comments: 20 pages, 10 figures, 6 tables, accepted by ApJ

The Star-Forming Main Sequence in JADES and CEERS at $z>1.4$: Investigating the Burstiness of Star Formation

Authors: Leonardo Clarke, Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Gabriel B. Brammer, Trinity Bento, Naveen A. Reddy, Emily Kehoe

Abstract: We have used public JWST/NIRSpec and JWST/NIRCam observations from the CEERS and JADES surveys in order to analyze the star-forming main sequence (SFMS) over the redshift range $1.4 \leq z < 7$. We calculate the star-formation rates (SFRs) of the galaxy sample using three approaches: Balmer line luminosity, spectral energy distribution (SED) fitting, and UV luminosity. We find a larger degree of s… ▽ More We have used public JWST/NIRSpec and JWST/NIRCam observations from the CEERS and JADES surveys in order to analyze the star-forming main sequence (SFMS) over the redshift range $1.4 \leq z < 7$. We calculate the star-formation rates (SFRs) of the galaxy sample using three approaches: Balmer line luminosity, spectral energy distribution (SED) fitting, and UV luminosity. We find a larger degree of scatter about the SFMS using the Balmer-based SFRs compared to the UV-based SFRs. Because these SFR indicators are sensitive to star formation on different time scales, the difference in scatter may be evidence of bursty star-formation histories in the early universe. We additionally compare the H$α$-to-UV luminosity ratio (L(H$α$)/$ν$L$_{ν,1600}$) for individual galaxies in the sample and find that 29\%$-$52\% of the ratios across the sample are poorly described by predictions from a smooth star-formation history. Measuring the burstiness of star formation in the early universe has multiple significant implications, such as deriving accurate physical parameters from SED fitting, explaining the evolution of the UV luminosity function, and providing constraints for sub-grid models of feedback in simulations of galaxy formation and evolution. △ Less

Submitted 24 October, 2024; v1 submitted 7 June, 2024; originally announced June 2024.

Comments: 23 pages, 7 figures, accepted by ApJ

The First Billion Years, According to JWST

Authors: Angela Adamo, Hakim Atek, Micaela B. Bagley, Eduardo Bañados, Kirk S. S. Barrow, Danielle A. Berg, Rachel Bezanson, Maruša Bradač, Gabriel Brammer, Adam C. Carnall, John Chisholm, Dan Coe, Pratika Dayal, Daniel J. Eisenstein, Jan J. Eldridge, Andrea Ferrara, Seiji Fujimoto, Anna de Graaff, Melanie Habouzit, Taylor A. Hutchison, Jeyhan S. Kartaltepe, Susan A. Kassin, Mariska Kriek, Ivo Labbé, Roberto Maiolino , et al. (24 additional authors not shown)

Abstract: 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.… ▽ More 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. △ Less

Submitted 31 May, 2024; originally announced May 2024.

Comments: review article written by the attendees of the 2024 ISSI breakthrough workshop "The first billion year of the Universe", submitted. Comments welcome