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1. Emission-line Diagnostics at z > 4: [OIII]λ4364 / Hγ versus [NeIII]λ3870 / [OII]λ3730

   https://doi.org/10.3847/1538-4357/ae1136  

   Backhaus, Bren E; Cleri, Nikko J; Trump, Jonathan R; Kirkpatrick, Allison; Simons, Raymond C; Amorín, Ricardo O; Arrabal_Haro, Pablo; Bagley, Micaela B; Brooks, Madisyn; Calabrò, Antonello; et al (November 2025, The Astrophysical Journal)

   We use JWST Near-Infrared Spectrograph observations from the Cosmic Evolution Early Release survey, GLASS-JWST ERS (GLASS), and JWST Advanced Deep Extragalactic Survey to measure rest-frame optical emission-line ratios of 89 galaxies atz > 4. The stacked spectra of galaxies with and without a broad-line feature reveal a difference in the [Oiii]λ4364 and Hγratios. This motivated our investigation of the [Oiii]λ4364/Hγversus [Neiii]/[Oii] diagram. We define two active galactic nucleus (AGN)/star formation (SF) classification lines based on 21,048 Sloan Digital Sky Survey galaxies atz ∼ 0. After applying a redshift correction to the AGN/SF lines, we find 69.2% of broad-line active galactic nuclei (BLAGN) continue to land in the AGN region of the diagnostic, largely due to the [Neiii]/[Oii] ratio. However, 33.0% of non-BLAGN land is in the AGN region as well. The [Oiii]λ4364/Hγversus [Neiii]/[Oii] diagram does not robustly separate BLAGN from non-broad-line galaxies atz> 4. This could be due to star-forming galaxies having harder ionization, or these galaxies contain a narrow line AGN, which are not accounted for. We further inspected galaxies without broad emission lines in each region of [Oiii]λ4364/Hγversus [Neiii]/[Oii] diagram and found that they have slightly stronger Ciii]λ1908 fluxes and equivalent width when landing in the BLAGN region. However, the cause of this higher ionization is unclear and may be revealed by observing UV lines. 

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2. Nuclear Activity in the Low-metallicity Dwarf Galaxy SDSS J0944-0038 : A Glimpse into the Primordial Universe

   https://doi.org/10.3847/2041-8213/acb4e4  

   Reefe, Michael; Satyapal, Shobita; Sexton, Remington O.; Secrest, Nathan J.; Matzko, William; Schwartzman, Emma; Nyland, Kristina; Canalizo, Gabriela; Rothberg, Barry; Pfeifle, Ryan W.; et al (March 2023, The Astrophysical Journal Letters)

   Abstract Local low-metallicity dwarf galaxies are relics of the early universe and are thought to hold clues into the origins of supermassive black holes. While recent studies are uncovering a growing population of active galactic nuclei (AGNs) in dwarf galaxies, the vast majority reside in galaxies with solar or supersolar metallicities and stellar masses comparable to that of the LMC. Using Multi-Unit Spectroscopic Explorer (MUSE) and Very Large Telescope observations, we report the detection of [Fex]λ6374 coronal line emission and a broad Hαline in the nucleus of SDSS J094401.87−003832.1, a nearby (z= 0.0049) metal-poor dwarf galaxy almost 500 times less massive than the LMC. Unlike the emission from the lower-ionization nebular lines, the [Fex]λ6374 emission is compact and centered on the brightest nuclear source, with a spatial extent of ≈100 pc, similar to that seen in well-known AGNs. The [Fex] luminosity is ≈10³⁷erg s⁻¹, within the range seen in previously identified AGNs in the dwarf-galaxy population. The [Fex] emission has persisted over the roughly 19 yr time period between the SDSS and MUSE observations, ruling out supernovae as the origin for the emission. The FWHM of the broad component of the Hαline is 446 ± 17 km s⁻¹and its luminosity is ≈1.5 × 10³⁸erg s⁻¹, corresponding to a black hole mass of ≈ 3150M_⊙, in line with its stellar mass if virial mass relations and black hole–galaxy scaling relations apply in this mass regime. These observations, together with previously reported multiwavelength observations, can most plausibly be explained by the presence of an accreting intermediate-mass black hole in a primordial galaxy analog. 

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3. Disentangling the Physical Origin of Emission Line Ratio Offsets at High Redshift with Spatially Resolved Spectroscopy

   https://doi.org/10.3847/1538-4357/ac1d52  

   Hirtenstein, Jessie; Jones, Tucker; Sanders, Ryan L.; Martin, Crystal L.; Cooper, M. C.; Brammer, Gabriel; Treu, Tommaso; Schmidt, Kasper; Shapley, Alice (November 2021, The Astrophysical Journal)

   Abstract We present spatially resolved Hubble Space Telescope grism spectroscopy of 15 galaxies at z ∼ 0.8 drawn from the DEEP2 survey. We analyze H α +[N ii ], [S ii ], and [S iii ] emission on kiloparsec scales to explore which mechanisms are powering emission lines at high redshifts, testing which processes may be responsible for the well-known offset of high-redshift galaxies from the z ∼ 0 locus in the [O iii ]/H β versus [N ii ]/H α Baldwin—Phillips—Terlevich (BPT) excitation diagram. We study spatially resolved emission-line maps to examine evidence for active galactic nuclei (AGN), shocks, diffuse ionized gas (DIG), or escaping ionizing radiation, all of which may contribute to the BPT offsets observed in our sample. We do not find significant evidence of AGN in our sample and quantify that, on average, AGN would need to contribute ∼25% of the H α flux in the central resolution element in order to cause the observed BPT offsets. We find weak (2 σ ) evidence of DIG emission at low surface brightnesses, yielding an implied total DIG emission fraction of ∼20%, which is not significant enough to be the dominant emission line driver in our sample. In general we find that the observed emission is dominated by star-forming H ii regions. We discuss trends with demographic properties and the possible role of α -enhanced abundance patterns in the emission spectra of high-redshift galaxies. Our results indicate that photoionization modeling with stellar population synthesis inputs is a valid tool to explore the specific star formation properties which may cause BPT offsets, to be explored in future work. 

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4. Mapping AGN winds: A connection between radio-mode AGNs and the AGN feedback cycle

   https://doi.org/10.1051/0004-6361/202451738  

   Albán, M; Wylezalek, D; Comerford, J M; Greene, J E; Riffel, R A (November 2024, Astronomy & Astrophysics)

   We present a kinematic analysis based on the large integral field spectroscopy (IFS) dataset of SDSS-IV MaNGA (Sloan Digital Sky Survey/Mapping Nearby Galaxies at Apache Point Observatory; ∼10 000 galaxies). We have compiled a diverse sample of 594 unique active galactic nuclei (AGNs), identified through a variety of independent selection techniques, encompassing radio (1.4 GHz) observations, optical emission-line diagnostics (BPT), broad Balmer emission lines, mid-infrared colors, and hard X-ray emission. We investigated how ionized gas kinematics behave in these different AGN populations through stacked radial profiles of the [O III] 5007 emission-line width across each AGN population. We contrasted AGN populations against each other (and non-AGN galaxies) by matching samples by stellar mass, [O III] 5007 luminosity, morphology, and redshift. We find similar kinematics between AGNs selected by BPT diagnostics compared to broad-line-selected AGNs. We also identify a population of non-AGNs with similar radial profiles as AGNs, indicative of the presence of remnant outflows (or fossil outflows) of past AGN activity. We find that purely radio-selected AGNs display enhanced ionized gas line widths across all radii. This suggests that our radio-selection technique is sensitive to a population in which AGN-driven kinematic perturbations have been active for longer durations (potentially due to recurrent activity) than in purely optically selected AGNs. This connection between radio activity and extended ionized gas outflow signatures is consistent with recent evidence that suggests radio emission (expected to be diffuse) originated due to shocks from outflows. We conclude that different selection techniques can trace different AGN populations not only in terms of energetics but also in terms of AGN evolutionary stages. Our results are important in the context of the AGN duty cycle and highlight integral field unit data’s potential to deepen our knowledge of AGNs and galaxy evolution. 

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5. CLEAR: Emission-line Ratios at Cosmic High Noon

   https://doi.org/10.3847/1538-4357/ac3919  

   Backhaus, Bren E.; Trump, Jonathan R.; Cleri, Nikko J.; Simons, Raymond; Momcheva, Ivelina; Papovich, Casey; Estrada-Carpenter, Vicente; Finkelstein, Steven L.; Matharu, Jasleen; Ji, Zhiyuan; et al (February 2022, The Astrophysical Journal)

   Abstract We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies at z ∼ 1.5 in the CANDELS Ly α Emission at Reionization survey. We compare [O iii ]/H β versus [S ii ]/(H α + [N ii ]) as an “unVO87” diagram for 461 galaxies and [O iii ]/H β versus [Ne iii ]/[O ii ] as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Ne v ] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures at z > 1. The OHNO diagram does effectively separate X-ray AGN and [Ne v ]-emitting galaxies from the rest of the population. We find that the [O iii ]/H β line ratios are significantly anticorrelated with stellar mass and significantly correlated with log ( L H β ) , while [S ii ]/(H α + [N ii ]) is significantly anticorrelated with log ( L H β ) . Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [O iii ]/H β versus [Ne iii ]/[O ii ] will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope. 

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