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1. MOSDEF-3D: Keck/OSIRIS Maps of the Ionized Interstellar Medium in z ∼ 2 Galaxies

   https://doi.org/10.3847/1538-4357/ae5704  

   Lam, Natalie; Shapley, Alice E; Sanders, Ryan L; Do, Tuan; Jones, Tucker; Coil, Alison; Kriek, Mariska; Mobasher, Bahram; Reddy, Naveen A; Siana, Brian; et al (April 2026, The Astrophysical Journal)

   Abstract We present spatially resolved rest-frame optical emission line maps of four galaxies atz ∼ 2 observed with the Keck/OH-Suppressing Infra-Red Imaging Spectrograph to study the physical conditions of the interstellar medium (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 Baldwin–Phillips–Terlevich diagram but agrees with other star-forming galaxies at similar redshifts. Despite the offset toward higher [Oiii]λ5008/Hβand [Nii]λ6585/Hα, these strong line ratios remain consistent with or below the maximum starburst threshold even in the inner ∼1 kpc region of the galaxies, providing no compelling evidence for central active galactic nucleus activity. The galaxies also exhibit flat radial gas-phase metallicity gradients, consistent with previous studies ofz ∼ 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. 

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2. The MOSDEF survey: a comprehensive analysis of the rest-optical emission-line properties of z ∼ 2.3 star-forming galaxies

   https://doi.org/10.1093/mnras/stab119  

   Runco, Jordan N; Shapley, Alice E; Sanders, Ryan L; Topping, Michael W; Kriek, Mariska; Reddy, Naveen A; Coil, Alison L; Mobasher, Bahram; Siana, Brian; Freeman, William R; et al (February 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We analyse the rest-optical emission-line spectra of z ∼ 2.3 star-forming galaxies in the complete MOSFIRE Deep Evolution Field (MOSDEF) survey. In investigating the origin of the well-known offset between the sequences of high-redshift and local galaxies in the [O iii]λ5008/Hβ versus [N ii]λ6585/Hα (‘[N ii] BPT’) diagram, we define two populations of z ∼ 2.3 MOSDEF galaxies. These include the high population that is offset towards higher [O iii]λ5008/Hβ and/or [N ii]λ6585/Hα with respect to the local SDSS sequence and the low population that overlaps the SDSS sequence. These two groups are also segregated within the [O  iii]λ5008/Hβ versus [S ii]λλ6718,6733/Hα and the [O iii]λλ4960,5008/[O ii ]λλ3727,3730 (O32) versus ([O  iii]λλ4960,5008+[O ii]λλ3727,3730)/Hβ (R23) diagrams, which suggests qualitatively that star-forming regions in the more offset galaxies are characterized by harder ionizing spectra at fixed nebular oxygen abundance. We also investigate many galaxy properties of the split sample and find that the high sample is on average smaller in size and less massive, but has higher specific star formation rate (SFR) and SFR surface density values and is slightly younger compared to the low population. From Cloudy+BPASS photoionization models, we estimate that the high population has a lower stellar metallicity (i.e. harder ionizing spectrum) but slightly higher nebular metallicity and higher ionization parameter compared to the low population. While the high population is more α-enhanced (i.e. higher α/Fe) than the low population, both samples are significantly more α-enhanced compared to local star-forming galaxies with similar rest-optical line ratios. These differences must be accounted for in all high-redshift star-forming galaxies – not only those ‘offset’ from local excitation sequences. 

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3. Emission-line Ratios and Ionization Conditions of CEERS Star-forming Galaxies with JWST/NIRSpec

   https://doi.org/10.3847/2515-5172/ad888e  

   Gupta, Ansh R; Kirkpatrick, Allison; Fernández, Vital; Arrabal_Haro, Pablo; Backhaus, Bren E; Cleri, Nikko J; Grogin, Norman A; Koekemoer, Anton M (October 2024, Research Notes of the AAS)

   Abstract Galaxy emission-line fluxes can constrain star formation rates (SFRs) and interstellar medium (ISM) ionization. We investigate rest-frame optical emission lines of 71 star-forming galaxies (SFGs) at redshift 0.7 < z < 7 using JWST/NIRSpec measurements from the Cosmic Evolution Early Release Science survey. We use Hαto measure SFR and utilize Hubble Space Telescope CANDELS stellar mass estimates to determine specific SFR (sSFR) and compare with the SFG main sequence (MS). We create [O iii]λ5008/Hβversus [Ne iii]λ3870/[O ii]λ3728 line ratio diagrams. The line ratios appear to correlate with sSFR, and our results suggest that sSFR is the parameter that governs ionization conditions rather than SFR or a galaxy’s distance from the MS. These measurements reveal a rich diversity of ISM conditions and physical galaxy properties throughout cosmic time. 

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4. Ultra-deep Keck/MOSFIRE Spectroscopic Observations of z ∼ 2 Galaxies: Direct Oxygen Abundances and Nebular Excitation Properties

   https://doi.org/10.3847/1538-4357/acfedb  

   Clarke, Leonardo; Shapley, Alice; Sanders, Ryan L; Topping, Michael W; Jones, Tucker; Kriek, Mariska; Reddy, Naveen A; Stark, Daniel P; Tang, Mengtao (November 2023, The Astrophysical Journal)

   Abstract Using deep near-infrared Keck/MOSFIRE observations, we analyze the rest-optical spectra of eight star-forming galaxies in the COSMOS and GOODS-N fields. We reach integration times of ∼10 hr in the deepest bands, pushing the limits on current ground-based observational capabilities. The targets fall into two redshift bins, of five galaxies atz∼ 1.7 and three galaxies atz∼ 2.5, and were selected as likely to yield significant auroral-line detections. Even with long integration times, detection of the auroral lines remains challenging. We stack the spectra together into subsets based on redshift, improving the signal-to-noise ratio on the [Oiii]λ4364 auroral emission line and, in turn, enabling a direct measurement of the oxygen abundance for each stack. We compare these measurements to commonly employed strong-line ratios alongside measurements from the literature. We find that the stacks fall within the distribution ofz> 1 literature measurements, but a larger sample size is needed to robustly constrain the relationships between strong-line ratios and oxygen abundance at high redshift. We additionally report detections of [Oi]λ6302 for nine individual galaxies and composite spectra of 21 targets in the MOSFIRE pointings. We plot their line ratios on the [Oiii]λ5008/Hβversus [Oi]λ6302/Hαdiagnostic diagram, comparing our targets to local galaxies and Hiiregions. We find that the [Oi]/Hαratios in our sample of galaxies are consistent with being produced in gas ionized byα-enhanced massive stars, as has been previously inferred for rapidly forming galaxies at early cosmic times. 

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5. A GLIMPSE into the very faint end of the H β +[O III] λλ 4960,5008 luminosity function at z ∼ 7 – 9 behind Abell S1063

   https://doi.org/10.1051/0004-6361/202556868  

   Korber, Damien; Chemerynska, Iryna; Furtak, Lukas J; Atek, Hakim; Endsley, Ryan; Schaerer, Daniel; Chisholm, John; Kokorev, Vasily; Saldana-Lopez, Alberto; Adamo, Angela; et al (April 2026, Astronomy & Astrophysics)

   We used the ultra-deep GLIMPSE JWST/NIRCam survey to constrain the faint end of the [O III]+Hβluminosity function (LF) down to 10³⁹erg s⁻¹atz ∼ 7 − 9 behind the lensed Hubble Frontier Field galaxy cluster Abell S1063. We applied a spectral energy distribution fitting on a Lyman-break galaxy selected sample of 164 lensed galaxies and measured their combined Hβ+[O III]λλ4960, 5008 flux to build the emission line LF. We found a [O III]+HβLF with a faint-end slope (α= −1.78^+0.06_−0.06forz = 7 − 8 andα= −1.55^+0.11_−0.11forz = 8 − 9), which is flatter than the UV LF at similar redshifts (α ≤ −2) and suggests a lower number density of weak [O III]+Hβemitting galaxies at fixedM_UV. We analysed several possible explanations: (i) a decrease in the [O III]+Hβ-to-UV ratio due to bursty star formation histories (SFHs), (ii) the effect of metallicity on the [O III]-to-Hβratio, or (iii) signs of a faint-end turnover in the UV LF. Under the assumption of an evolving [O III]-to-Hβratio, we separated the contribution of [O III]λ5008 and Hβand obtained a flatter [O III]λ5008 LF (α= −1.66^+0.05_−0.05forz = 7 − 8 andα= −1.45^+0.09_−0.10forz = 8 − 9) but steeper HβLF ($$ \alpha=-1.95_{-0.08}^{+0.08} $$ forz = 7 − 8 andα= −1.68^+0.13_−0.14forz = 8 − 9). The combination of a decreasing metallicity and bursty SFH can reconcile the observed differences between the UV and [O III]+HβLF. By converting this LF into the ionising photon-production rateṄ_ion, we show that galaxies withL_Hα ≥ 10³⁹erg s⁻¹, that is, with a star formation rate (SFR) (Hα)  ≥  5 × 10⁻³M_⊙yr⁻¹) cause 31%−90% and 46%−156% of the ionising photon budget (at 7 < z < 8 and 8 < z < 9), when we assume a constant escape fraction of Lyman-continuum photon (f_esc = 0.14). The shape of the LF further shows the negligible contribution of faint galaxies to theṄ_ion. Additionally, we derived the cosmic star formation rate density (SFRD), finding results consistent with previous estimates. However, the sensitivity of GLIMPSE to lower SFRs reinforces the conclusion that very faint galaxies contribute very little toṄ_ionand the SFRD. Our results suggests that GLIMPSE has detected the bulk of the total [O III]+Hβemission from star-forming galaxies, and that galaxies below our detection limits are likely minor contributors to cosmic re-ionisation. 

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