Weekly issue

Week 39, 2026

Sep 21–27, 2026

Week 39, 2026 includes 17 curated papers, centered on spectroscopy, LRD, high-z.

2609.27130v1

Search for High-Ionization Nebular Emission (SHINE). I. A Systematically Selected [Ne V] Sample at z > 3 with JWST/NIRSpec PRISM

Shobita Satyapal, Sara Doan, Daniel Schaerer, Rui Marques-Chaves, Anurag Sawarkar, William Matzko, Camilo Vazquez, C. Daoutis, D. Korber, I. Morel, Mengyuan Xia

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SHINE presents the first systematic [Ne V]λ3426 search in JWST/NIRSpec PRISM spectra at z>3, identifying 25 luminous emitters from a parent sample of more than 9,000 galaxies across z=3.059–9.444. Their [Ne V] luminosities and hard line ratios favor black-hole accretion, yet the sample is heterogeneous in morphology, stellar mass, continuum shape, and broad-Balmer properties, and overlaps only partly with standard broad-line and rest-optical narrow-line AGN selections. Six secure Chandra counterparts demonstrate that X-ray weakness is not universal, while the lack of significant evolution in the observed luminous [Ne V] incidence supports [Ne V] as a complementary route to finding early accretion beyond conventional JWST AGN selections.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This establishes the selection’s luminosity regime: SHINE [Ne V] emitters overlap local [Ne V]-selected AGNs and sit above the known local metal-poor comparison population, framing why accretion is favored for the detected sources.
Figure 4. The high-ionization diagnostic planes show where the 25 [Ne V] sources fall relative to JWST broad-line AGNs, LRDs, narrow-line selections, local AGNs, and metal-poor galaxies, directly illustrating the sample’s incomplete overlap with conventional AGN criteria.
Figure 6. This comparison tests whether independently selected broad-line AGNs, LRDs, and S2–VO87 AGNs lack [Ne V] relative to [Ne III]; the shallow upper limits make clear why the paper cannot claim a population-wide [Ne V] deficit in those samples.
Figure 10. This is the population-level conclusion figure: after imposing a common apparent [Ne V] luminosity threshold and sensitivity requirement, the observed luminous-emitter fraction shows no significant evolution across z>3, with the stated caveat that it is not completeness-corrected.

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2609.22507v1

Inflated Supermassive Stars as Little Red Dots and Progenitors of Supermassive Black Holes

Wenbin Lu

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Lu develops hydrostatic, thermally relaxed models of metal-enriched, hydrogen-burning supermassive stars as a stellar interpretation for JWST little red dots. In the most metal-rich cases, an iron-opacity bump inflates a low-mass envelope to cool photospheric temperatures near 7000 K, producing compact, luminous, nearly Eddington sources in the LRD-like regime while naturally remaining weak in X-rays and high-ionization lines. General-relativistic instability limits their masses to roughly 3×10^5–3×10^6 Msun depending on core rotation, yielding a luminosity ceiling near 10^44 erg s^-1 that matches the observed bright-end LRD cutoff; hydrogen depletion can then trigger collapse after about 1 Myr, leaving massive black-hole seeds. The key caveat is atmospheric physics: non-LTE Lyα trapping and hydrogen-level populations could substantially alter Balmer features, continuum opacity, and the predicted effective temperature.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 7. This HR diagram provides the clearest population-level link to LRD phenomenology: increasing metallicity moves the models onto a cool, inflated branch, with Z≈10^-2 solutions reaching the LRD-like temperature range while retaining near-Eddington luminosities.
Figure 9. This figure shows how general-relativistic instability sets the model’s maximum mass and how rotation materially shifts that threshold, underpinning the proposed 3×10^5–3×10^6 Msun progenitor mass range and luminosity cutoff.
Figure 11. This remnant-abundance calculation connects the short SMS phase to the present-day supermassive-black-hole population, showing that an order-1 Myr lifetime can yield a descendant density comparable to local SMBH estimates after allowing for mergers.
Figure 1. The representative stellar cross section makes the physical mechanism concrete: a CNO-burning core radiates near the Thomson Eddington limit, while the Fe-opacity bump drives the extended convective envelope that creates the cool photosphere.

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2609.20920v1

Little Red Dots As Super-Eddington Fountain Flows

Nicholas Kaaz, Eliot Quataert, Taya Govreen-Segal, Hanpu Liu

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Kaaz et al. propose that little red dots are off-axis, super-Eddington accretors embedded in slow, marginally unbound, potentially photon-tired winds, while faster outflows escape through polar funnels. Their Sirocco radiative-transfer models reproduce a progression from little blue dots to V-shaped and fully red LRD spectra as the wind mass-loss rate rises, and produce P Cygni absorption atop broad electron-scattering wings. The key physical ingredient is a Compton-thick “Balmer cocoon,” where Lyman-α trapping maintains the hydrogen n=2 population and Balmer-continuum depletion, rather than Lyman-continuum absorption alone, controls ionization and enables strong Balmer breaks at comparatively modest densities.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 2. This figure frames the paper’s central motivation by comparing the observed 100–300 km s⁻¹-scale line-trough offsets and narrow-core velocities with the much faster winds expected from ordinary super-Eddington disk launching and thermal-photosphere escape speeds. It makes the case that the relevant LRD outflow must be slow and only marginally unbound.
Figure 4. The synthetic continua show the paper’s main phenomenological result: increasing mass loss transforms a little-blue-dot spectrum into a V-shaped LRD with a partial Balmer break and then a red source with a complete break. This is the clearest figure for assessing whether the fountain-wind models span the observed diversity of LRD spectral shapes.
Figure 5. These synthetic Balmer-line profiles connect the model directly to the defining spectroscopy of LRDs, combining narrow emission cores and blueshifted P Cygni absorption with broad exponential electron-scattering wings. The figure supports the argument that broad wings need not imply correspondingly rapid bulk gas motions.
Figure 13. This figure isolates the proposed Balmer-cocoon physics by showing that the simulated n=2 neutral-hydrogen abundance beyond the Lyman transition radius follows Balmer-continuum photoionization equilibrium rather than local thermodynamic equilibrium. It provides the most direct physical diagnostic for why strong Balmer opacity and breaks can arise in these non-LTE winds.

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2609.29072v1

High-z galaxies with the JWST and the ELT: Toward Ever-finer Detail

Eros Vanzella

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Vanzella reviews how JWST’s infrared imaging and spectroscopy have opened the first half-gyr of cosmic history to resolved studies of massive blue and red galaxies, little red dots, metal-poor systems, and lensed star-forming clumps. The central forward-looking result is that diffraction-limited ELT imaging, with near-infrared PSF FWHM of roughly 8–12 mas, should resolve sub-100-pc scales at essentially any redshift up to z≈18, about six times finer than JWST. Combined with moderate gravitational magnification (μ≈4–8), ELT and adaptive-optics facilities could routinely reach ≲25-pc, star-cluster-scale structure in distant galaxies, connecting early star formation, bound clusters, and possible black-hole-seed environments.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This figure establishes the paper’s core resolution argument by comparing the physical scales reached by HST, JWST, VLT/MAVIS, and ELT/MORFEO–MICADO over redshift. It makes clear why a 10-mas-class ELT PSF changes the science case from galaxy-scale morphology to resolving ∼100-pc structures even in the earliest accessible galaxies.
Figure 2. This diagnostic combines telescope diffraction limit with lensing magnification for a source at z=10, directly quantifying the route to star-cluster-scale measurements. It shows that modest magnification lets the ELT probe below 25 pc, while stronger lensing opens sub-parsec regimes that the paper identifies as genuinely new observational territory.

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2609.26999v1

The lifetimes and properties of Little Red Dots in the AMBRA simulation

Patrick LaChance, Yihao Zhou, Aklant Kumar Bhowmick, Rupert A. C. Croft, Tiziana Di Matteo, Laura Blecha, Fabio Pacucci, Paul Torrey, Simeon Bird

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LaChance et al. build mock JWST photometry for AMBRA black hole–galaxy systems at z=5–8 and apply LRD color and compactness selection under both standard and gas-enshrouded AGN emission models. A gas-enshrouded AGN is essential for reproducing the dim F444W>26 LRDs, while added unresolved AGN variability flattens AMBRA’s otherwise overly steep decline in LRD abundance toward high redshift. The simulated LRDs are not a distinct newborn population but ordinary pre-existing black hole–host systems caught in an AGN-dominated observable phase. Their inferred LRD windows are mostly ~3–300 Myr, rising with black hole and host mass: lower-mass, enshrouded systems persist for roughly 30 Myr, whereas compact higher-mass hosts can remain LRDs for roughly 100 Myr or longer.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 3. This is the selection-function figure: it shows how the mock AMBRA population occupies the color–magnitude, color–color, and compactness cuts, and directly contrasts the gas-enshrouded and standard AGN prescriptions used to define simulated LRDs.
Figure 6. This figure carries the population-level comparison, showing AMBRA’s redshift evolution against observational estimates and other theoretical datasets. It makes clear why unresolved luminosity variability is consequential: it flattens the predicted decline toward z~8 and brings the model closer to the observed trend.
Figure 9. This diagnostic establishes the paper’s physical interpretation of selection by showing the AGN contribution to F444W emission across the AMBRA population. It supports the conclusion that an LRD phase is primarily set by the AGN becoming bright relative to its host rather than by a wholly separate class of objects.
Figure 11. This is the conclusion-driving lifetime measurement, relating the duration of each LRD window to host stellar mass, black hole mass, and bolometric luminosity. It captures the central mass dependence and the important caveat that ongoing high-mass phases provide lower limits rather than fully measured durations.

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2609.25349v1

Calcium Triplet Absorption is Common around Little Red Dots

Jenny E. Greene, Hanpu Liu, Raphael E. Hviding, Rohan P. Naidu, David J. Setton, Bingjie Wang, Ivo Labbe, Vasily Kokorev, Xiaojing Lin, Hollis B. Akins, Anna de Graaff, Joel Leja, Jorryt Matthee, Alberto Torralba, Karl Glazebrook, Rachel Bezanson, Leindert A. Boogaard, Gabriel Brammer, Caitlin M. Casey, John Chisholm, Xiaohui Fan, Lukas Furtak, Seiji Fujimoto, Yan-Fei Jiang, Yilun Ma, Themiya Nanayakkara, Erica J. Nelson, Richard Pan, Eliot Quataert, Anthony J. Taylor, Christina Williams, Adi Zitrin

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Using JWST/NIRSpec grating spectra of 17 spectroscopically identified little red dots at 2 < z < 5, Greene et al. search the rest-frame 8500 Å region for calcium-triplet absorption, a stellar-atmosphere-like feature previously seen in the local LRD analog the Egg. They detect CaT absorption in three individual sources, including the robust JADES-28074/Rosetta Stone case, and obtain a stacked mean equivalent width of roughly −5 Å, arguing that the absorption is associated with the central engine rather than host starlight. The result supplies direct evidence for cool, optically thick gas around LRDs: the observed strengths can arise in low-metallicity hydrostatic photospheres with T_eff > 4500 K, or in lower-density gas whose required structure is dynamically non-hydrostatic.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. Shows the individual CaT detections and matched non-detections, making the line-model decomposition and the strength of the JADES-28074/Rosetta Stone evidence immediately visible. It also conveys the important fit sensitivity in GLIMPSE ID17775 and the role of broad CaT emission in setting the local continuum.
Figure 2. Presents the stack across the full grating sample, demonstrating that CaT absorption persists at similar depth even beyond the individually detected objects. This is the clearest population-level evidence that the feature is common around LRDs rather than confined to a few exceptional spectra.
Figure 3. Places individual CaT measurements, upper limits, the stack, and the low-redshift analogs on a common equivalent-width versus optical-luminosity plane. The figure shows that the limited current sample does not establish a significant CaT–luminosity trend despite the unusually strong absorption in the Egg.
Figure 4. Connects the observed CaT equivalent-width distribution to atmosphere calculations, isolating the temperature, metallicity, and surface-gravity or density conditions compatible with the data. It is the conclusion-driving physical diagnostic and makes clear the systematic uncertainty from unknown triplet line ratios and possible line or continuum infill.

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2609.26553v1

Constraining Inflation with Little Red Dots

Dionysios Karagiannis, P. Daniel Meerburg

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Karagiannis and Meerburg forecast how a 14,000 deg² spectroscopic survey of JWST little red dots across 4<z<9 could constrain primordial non-Gaussianity through the joint redshift-space galaxy power spectrum and bispectrum. Using an HOD-calibrated LRD bias hierarchy, 32 marginalized nuisance parameters, and a non-Gaussian bispectrum covariance, they obtain σ(fNLloc)=0.32, σ(fNLequil)=32, and σ(fNLorth)=10. The local result would improve on Planck by a factor of 16 and fall roughly threefold below the σ(fNLloc)≈1 benchmark separating broad single- and multi-field inflation classes, making LRD clustering a compelling science case for wide near- to mid-infrared spectroscopy. A central forecasting lesson is that non-Gaussian covariance degrades the local constraint by a factor of four to six relative to a Gaussian-diagonal treatment, because squeezed configurations are strongly coupled.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This is the headline comparison: it places the conservative LRD forecast for local, equilateral, and orthogonal PNG alongside selected CMB and large-scale-structure forecasts, directly showing the claimed improvement over Planck and the crossing of the σ(fNLloc)=1 benchmark.
Figure 2. This figure identifies which assumptions control the forecast robustness. In particular, it shows that LRD abundance dominates the astrophysical uncertainty budget, while equilateral and orthogonal constraints are especially exposed because their information is carried by shot-noise-limited small-scale triangles.
Figure 5. This survey-area scaling figure translates the inflation forecast into an observational design requirement. It contrasts Gaussian and non-Gaussian covariance treatments across sky fraction and shows how the local, equilateral, and orthogonal constraints respond differently to widening the spectroscopic footprint.

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2609.22623v1

Balmer Absorption Series and Broad Metal Lines in Two Luminous Little Red Dots

Bingjie Wang, Jenny E. Greene, Hanpu Liu, Nicholas Kaaz, Gabriel B. Brammer, Raphael E. Hviding, Ivo Labbé, Joel Leja, Jorryt Matthee, Rohan P. Naidu, Alberto Torralba, Josephine F. W. Baggen, Nikko J. Cleri, Seiji Fujimoto, Lukas J. Furtak, Anna de Graaff, Michaela Hirschmann, Vasily Kokorev, Erini Lambrides, Ian McConachie, Erica J. Nelson, Adèle Plat, Weichen Wang, Adi Zitrin

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Using deep JWST/NIRSpec spectra of the exceptionally red, luminous LRDs RUBIES-EGS-49140 at z=6.68 and lensed UNCOVER-A2744-45924 at z=4.46, Wang et al. resolve near-systemic Balmer absorption from Hα through Hδ and broad metal-line emission. The Balmer troughs shift progressively redward at higher order while their equivalent widths decline much more weakly than a single foreground screen predicts; Ca II K instead follows Hα, pointing to stratified absorbing gas. Broad [Ne III], [O III], and He I emission, together with weak or absent He II and an unusually high He I λ7067/λ5877 ratio, favors very dense AGN gas over standard low-density photoionization models. The authors argue that optically thick re-emission can reshape the Balmer-series absorption strengths, while the velocity progression may trace a stratified, possibly failed-wind inflow geometry.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 2. Shows the resolved Hα–Hδ profile decompositions in both LRDs, establishing the deep near-systemic absorption and the distinct narrow, broad, and absorption components on which the paper’s Balmer-series results rest.
Figure 3. Condenses the velocity offsets and widths of all fitted components, making the mild but systematic redward shift of higher-order Balmer absorption immediately visible relative to narrow [O III] systemic redshifts.
Figure 6. Presents the metal-line fits that reveal broad [Ne III] and [O III] emission as well as Ca II K absorption, connecting the Balmer absorber to independent gas-phase diagnostics.
Figure 7. Provides the conclusion-driving photoionization comparison: both LRDs fall outside standard low-density AGN grids, while higher-density narrow-line-region models reach the observed ratios and support dense AGN gas.
Figure 8. Illustrates the proposed failed-wind interpretation in which Hα traces slow outer gas and higher-order Balmer lines probe deeper, faster infalling material, naturally producing the observed redward velocity progression.

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2609.24987v1

EPOCHS-DR2 I: Expanded data release and properties of $6.5<z<16.5$ photometrically selected galaxies across NIRCam deep fields covering $\sim700\,\rm arcmin^2$ with the galfind software

Duncan Austin, Christopher J. Conselice, Thomas Harvey, Nathan J. Adams, Louis Quilley, Jordan C. J. D'Silva, Vadim Rusakov, Qiong Li, Lewi Westcott, Caio Goolsby, James Arcidiacono, Kai Madgwick, William J. Roper, Brenda Frye, Norman A. Grogin, Rafael Ortiz, Rogier Windhorst

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EPOCHS-DR2 releases a homogeneous galfind-based catalog of 2,452 photometrically selected star-forming galaxies at 6.5<zphot<16.5 across six JWST/NIRCam deep fields spanning roughly 650–740 arcmin², together with imaging products, empirical PSFs, and multiple SED-fitting outputs. Its photo-z selection is benchmarked against 293 spectroscopic confirmations, achieving σNMAD=0.017 with a 4.3% outlier rate, while explicitly identifying and removing 34 V-shaped-SED little red dots and 107 brown-dwarf candidates. The catalog also isolates 62 zphot>10.5 “gold” candidates, including 15 at zphot>13.5; GS-W-4608 and GN-Med-1881 are particularly robust owing to very blue UV slopes, strong Lyman-break colors, and supporting F335M/F410M detections. The measured flattening of the βUV–MUV relation, with βUV(MUV=-19)≈-2.32 at z≈12.5, points to moderately dust-polluted stellar populations even at the highest redshifts.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 3. This is the clearest overview of the full photometric selection in redshift–UV-luminosity space, distinguishing the z>10.5 gold sample from the larger catalog and placing it alongside spectroscopically confirmed sources.
Figure 4. This diagnostic directly shows how the 34 LRDs and 107 brown-dwarf candidates separate from the fiducial galaxy sample in photometric-redshift, luminosity, compactness, and stellar-mass space, making the contaminant removal central to the release tangible.
Figure 5. The spectroscopic-versus-photometric redshift comparison substantiates the catalog’s claimed photo-z performance and explains the adoption of the sfhz_blue_agn template set as the fiducial solution.
Figure 11. This Lyman/Balmer-break versus UV/optical-slope diagnostic tests the most extreme zphot=13.5–16.5 gold candidates against likely z≈4 LRD and quiescent-galaxy contaminants, providing the key physical caveat for the highest-redshift sample.

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2609.24588v1

LATED: Ly$α$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon

Mingyu Li, Zheng Cai, Roberto Maiolino, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Qiao Duan, Eiichi Egami, Xiaohui Fan, Yuki Isobe, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Boyuan Liu, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, Zijin Su, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Hannah Übler, Yunjing Wu, Fujiang Yu, Zijian Zhang

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Li et al. introduce LATED, a Lyα-emitter–anchored three-band selection that uses the contrast between [O III]+Hβ, Hα, and nearby continuum emission to isolate metal-free and extremely metal-poor star-formation candidates across five windows at z=1.92–6.60. The method rejects ordinary enriched star-forming and AGN templates, flags little red dots through additional colours, selects none of 1,126 JADES spectroscopic galaxies in the NIRCam windows, and recovers the confirmed extremely metal-poor Abell 2744 source AMORE6 while identifying three new z=3–5 candidates. Its accompanying photometric line-inference package recovers spectroscopic R3=[O III]/Hβ with 0.12 dex scatter, making LATED a scalable way to prioritize targets for the spectroscopy still required to establish genuinely metal-free star formation.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This workflow figure succinctly shows the full LATED logic: a tomographic Lyα-emitter parent sample, redshift-window construction, the EW(Hα)–oxygen-abundance colour plane, little-red-dot contaminant flags, and photometric line-ratio inference feeding spectroscopic follow-up.
Figure 5. The W 2.1 selection plane demonstrates the core physical discriminator in practice: strong Hα combined with weak [O III]+Hβ places Pop III-like templates in a distinct colour corner, while the mock catalogue shows how photometric noise affects contamination and recovery.
Figure 10. This figure supplies the redshift-dependent x and y boundaries that operationalize LATED across all five windows, clarifying that the selection follows the extrema of the forward-modelled Pop III locus rather than imposing a single fixed colour cut.
Figure 15. The JADES validation directly supports the empirical cleanliness claim: 1,126 spectroscopically confirmed galaxies populate the four NIRCam colour planes but none satisfy the appropriate redshift-dependent LATED criteria.
Figure 20. This validation figure tests the released three-band inference machinery against simulations and NIRSpec measurements, showing how photometric [O III]/Hβ estimates and upper limits connect the candidate selection to a quantitative metallicity-sensitive diagnostic.

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2609.21337v1

A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30

Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer, Dazhi Zhou, Hollis Akins, Manuel Aravena, James R. Burgoyne, Caitlin M. Casey, Erin Foley, Leah Fryer, Ryley Hill, Nicholas LeVar, Monica Natalia Isla Llave, Matt Malkan, Vismaya Pillai, William Rasakanya, Manuel Solimano, Justin S. Spilker, Aurelie Torti, Joaquin D. Vieira, Fabio Vito, David Vizgan, George Wang

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Chapman et al. identify 11 ultra-red JWST/NIRCam sources in the compact core of the z=4.30 SPT2349-56 protocluster, selected by m200−m444 > 2.0 and reaching a projected number density at least 2000 times that of comparable field populations. Their colors overlap little red dot selections, but all except ERD5/LRD1 are resolved, favoring substantial stellar emission over continuum dominated by an unresolved AGN; ALMA Band 7 limits further place most of the extended red dots below the star-forming main sequence. ERD1/Q1 stands out as a bright, massive candidate quiescent or recently quenched member, making this core a striking coexistence of dusty starbursts and galaxies already transitioning toward the passive population, although spectroscopic confirmation of the red sources remains outstanding.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This JWST overview establishes the extraordinary spatial context: all 11 red sources sit in the SPT2349-56 core, including a compact subgroup of six ERDs near SMG-A amid known ALMA members and radio AGN.
Figure 2. This is the key selection and morphology diagnostic, showing the m200−m444 > 2.0 cut relative to cluster SMGs and field sources while separating the mostly resolved ERDs from the single source satisfying the compact LRD criterion.
Figure 5. The full ERD SED comparison connects the red colors to predominantly old stellar populations and low obscured-AGN contributions, while highlighting ERD1/Q1 as a massive system comparable in stellar mass to previously known high-SFR cluster members.
Figure 6. This figure carries the paper's central evolutionary claim by placing ERDs below the star-forming main sequence relative to the protocluster SMGs; the ALMA stack indicates that the population is quenched on average, with the high-mass end most clearly quiescent.

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2609.20913v1

Free-Free Radio Emission from Little Red Dots as a Probe of Ionized Gas

Takumi S. Tanaka, Kohei Inayoshi, Zu Yan, Tomokazu Kiyota, Yuichi Harikane, John D. Silverman

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Tanaka et al. propose thermal free-free radio emission as an independent probe of the dense ionized gas thought to surround little red dots. Free-free self-absorption should imprint a spectral turnover whose frequency and luminosity jointly constrain the electron column density and characteristic size of the ionized region, while the low-frequency slope distinguishes a uniform medium from a radially stratified one. Using representative low- and high-redshift LRDs, including J1025+1402 and A2744-45924, they show that 10-hour SKA1-Mid, ngVLA, and ALMA observations can access the relevant parameter space and recover column and size constraints from mock photometry. The approach offers a radio-to-millimeter test of whether the gas geometry invoked to explain LRD optical/infrared spectra is physically viable on unresolved scales.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This is the core observable-to-physics map: a turnover frequency and luminosity translate into ionized-region radius, electron column density, and density, while the shaded [O III] collisional-de-excitation regime marks an important physical boundary.
Figure 2. The representative SEDs make the proposal observationally concrete by placing Model II and density-gradient Model V free-free spectra beside A2744-45924 and J1025+1402, dust/blackbody alternatives, and instrument sensitivities.
Figure 3. This figure identifies which combinations of ionized-gas size and density are detectable in 10-hour SKA1-Mid, ngVLA, and ALMA exposures, directly testing the paper's feasibility claim across low- and high-redshift cases.
Figure 4. The mock-fitting posteriors show the diagnostic payoff after detection: even with an intrinsic degeneracy among temperature, size, and density-profile parameters, the electron column density and characteristic radius remain recoverable to useful precision.

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2609.30232v1

Breaking the Blend: A multi-tracer kinematic decomposition method for IFS data applied to disentangling the AGN outflow and circumnuclear ring in NGC 5728 with JWST

Oscar Veenema, Niranjan Thatte, Dimitra Rigopoulou, Richard I. Davies, Miguel Pereira-Santaella, Ismael García-Bernete, Almudena Alonso-Herrero, Anelise Audibert, Enrica Bellocchi, Andrew J. Bunker, Françoise Combes, Tanio Díaz Santos, Fergus R. Donnan, Donaji Esparza-Arredondo, Federico Esposito, Santiago García-Burillo, Begoña García-Lorenzo, Omaira Gonzalez Martin, Laura Hermosa Muñoz, Erin K. S. Hicks, Sebastian F. Hönig, Masatoshi Imanishi, Alvaro Labiano, Nancy A. Levenson, Enrique Lopez-Rodriguez, Cristina Ramos Almeida, Claudio Ricci, Rogemar A. Riffel, Marko Stalevski

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Veenema et al. introduce a spaxel-by-spaxel IFS decomposition framework that stacks kinematic information from multiple emission lines, then imposes those component kinematics to apportion flux between physically distinct structures. Applied to combined JWST/NIRSpec and MIRI/MRS data for the Compton-thick Seyfert 2 NGC 5728, the method uses twelve mid-infrared fine-structure lines spanning ionisation potentials of 7.9–126.2 eV to separate its circumnuclear star-forming ring from the AGN-driven biconical outflow. The resulting maps recover the detailed morphology of both components even where low-ionisation tracers blend ring and outflow emission, while high-ionisation [Ne V] is confined to the AGN/outflow. This provides a scalable route to interpreting blended line structures and deriving component-resolved IFS measurements across facilities and wavelength ranges.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This side-by-side comparison establishes the observational problem the method solves: low-ionisation [Ne II] contains both the circumnuclear ring and outflow signatures, whereas high-ionisation [Ne V] isolates the AGN and biconical outflow. The flux and velocity maps make the contrasting spatial and kinematic tracers immediately visible.
Figure 2. This is the conclusion-driving product of the stacked multi-line decomposition: the outflow flux-fraction map assigns each spaxel to AGN-driven outflow or star-forming disc dominance. It shows that the framework converts blended emission-line data into a physically interpretable, component-resolved view of the central region.

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2609.28474v1

A sub-100 pc view at z~5 of a Multiply-Imaged Massive Quiescent Galaxy

Richard Pan, Danilo Marchesini, Joseph F. V. Allingham, Seiji Fujimoto, Adi Zitrin, Dan Coe, Vasily Kokorev, Lukas J. Furtak, Jacqueline Antwi-Danso, Yoshihisa Asada, Franz E. Bauer, Maruša Bradač, Larry D. Bradley, Chloe M. Cheng, Pratika Dayal, Andreas L. Faisst, Brenda L. Frye, Norman A. Grogin, Tiger Yu-Yang Hsiao, Gourav Khullar, Anton M. Koekemoer, Conor Larison, Ray A. Lucas, Vladan Markov, Nicholas S. Martis, Minami Nakane, Gaël Noirot, Johan Richard, Massimo Ricotti, Luke Robbins, Fengwu Sun, Francesco Valentino, Eros Vanzella, Chris Willott, Rogier A. Windhorst, Hiroto Yanagisawa, Anita Zanella

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Pan et al. use cluster lensing by CL J0152.7-1357 to resolve the triply imaged post-starburst galaxy VENUS-CLJ0152-QG1 at z=5.18 on roughly 70 pc scales, far beyond the effective physical resolution available for comparable unlensed JWST targets. Spatially resolved mass, light, color, and medium-band line maps show an extended system with a half-light radius about twice that of field analogs, a central stellar-mass surface density lower by about 0.5 dex, and ionized-gas emission offset from the luminous core. The combination argues that this massive galaxy quenched abruptly without a preceding compact central buildup or an obvious unobscured AGN, implying that unresolved measurements can overstate early-galaxy densities and that models need quenching channels beyond compaction-driven evolution.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. Use this overview to establish the three lensed images of VCQG1, their consistent spectral breaks and redshift solutions, and the rapidly declining recent star-formation histories that motivate its post-starburst classification.
Figure 2. This is the central structural result: the lensing-resolved light, stellar-mass, and SFR-density maps show that VCQG1 is extended relative to field quiescent analogs and contains a localized star-forming enhancement offset from the light peak.
Figure 3. The resolved rest-frame UV-optical color diagnostics and radial gradients test quenching geometry directly, disfavoring uniform or inside-out quenching interpretations for the source.
Figure 4. This figure provides the clearest physical diagnostic for the paper's conclusion, showing that the medium-band emission-line excess is spatially separated from the stellar core; without lensing, it could be misidentified as a central starburst or AGN.

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2609.22428v1

Star Formation and Nebular Attenuation from Pa$α$, Br$α$, and Br$β$ in Massive Dust-obscured Galaxies at Cosmic Noon using JWST

Virginia Vanicek, Jed McKinney, Alexandra Pope, Anna Sajina, Stacey Alberts, Meredith Stone, Lee Armus, Sinclaire M. Manning, Olivia Cooper, Tanio DÍaz-Santos, Miriam Eleazer, Caitlin Casey, Thomas S. -Y. Lai, Steven Finkelstein, Leonid Sajkov, Allison Kirkpatrick, Anthony Taylor

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Vanicek et al. use combined JWST/MIRI LRS and archival Spitzer/IRS spectra to detect Paα, Brα, and Brβ in 27 massive infrared-luminous galaxies at z≈1–2, spanning star-forming systems, obscured AGN, and composites. Multiple recombination-line measurements yield substantial nebular attenuation, with Aλ≈3 mag near 2 μm but still ≈1 mag near 4 μm, demonstrating that even near-IR SFR indicators require meaningful dust corrections in these galaxies. The attenuation-corrected, ≈10 Myr nebular SFRs agree across Paα, Brα, and Brβ, yet remain systematically lower than standard LIR-based, ≈100 Myr SFRs by a factor of about 2.5. The mismatch suggests that IR luminosities may retain signatures of earlier star formation or receive additional heating from evolved stars and/or an AGN, complicating their interpretation as instantaneous SFRs at cosmic noon.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 5. This is the key attenuation result: it shows the line-by-line nebular extinction from Paα through Brα and directly establishes the strong wavelength dependence, including the contrast with continuum attenuation.
Figure 7. This comparison demonstrates that Paα-, Brα-, and Brβ-based SFRs converge after the authors' attenuation corrections, providing the internal validation for their recombination-line methodology.
Figure 8. This is the central timescale comparison, placing the short-timescale recombination-line SFRs against LIR-derived SFRs and visualizing the systematic offset that motivates the paper's physical interpretation.
Figure 10. This synthesis figure shows the consequence for galaxy classification: nebular-line SFRs place the sources closer to the mass–redshift main sequence, whereas LIR SFRs would label them as exclusively starburst systems.

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2609.26931v1

Radio Quasars in the Cosmic Dawn: A Spectroscopic Sample from the DESI Survey

Anniek J. Gloudemans, Jinyi Yang, David M. Alexander, Arjun Dey, Xiaohui Fan, Victoria A. Fawcett, Martin J. Hardcastle, Stephanie Juneau, George K. Miley, Leah K. Morabito, Adam D. Myers, Swayamtrupta Panda, Huub J. A. Röttgering, Timothy Shimwell, Daniel J. B. Smith, Feige Wang, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. Cuceu, A. de la Macorra, P. Doel, S. Ferraro, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, C. Hahn, M. Ishak, R. Joyce, R. Kehoe, D. Kirkby, T. Kisner, A. Kremin, M. Landriau, L. Le Guillou, M. E. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, W. J. Percival, F. Prada, I. Pérez-Ràfols, A. Robertson, G. Rossi, E. Sanchez, E. F. Schlafly, D. Schlegel, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, R. Zhou, H. Zou

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Gloudemans et al. assemble the largest spectroscopic sample of radio quasars at 4.7<z<6.7, matching 646 DESI-confirmed quasars to 144 MHz LoTSS-DR3 data and identifying 83 radio detections, including 26 radio-loud objects. Their 10^25-10^28 W Hz^-1 radio luminosities imply jet-dominated emission, establishing that powerful jets were already in place by z~5. Rest-UV composites and C IV velocity shifts are broadly indistinguishable from radio non-detections, although radio-detected sources have modestly smaller Lyα and C IV equivalent widths and no significant excess of weak-line quasars. BAL quasars are mainly radio-quiet, with no absorption-index--radio-loudness correlation, favoring physically distinct jet and BAL-outflow phenomena.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 2. This is the core sample-definition figure: it places the DESI-LoTSS quasars in radio-loudness--redshift space, shows the R>10 threshold, and demonstrates the substantial expansion of the known z>4.7 radio-quasar population.
Figure 5. This figure directly quantifies the weak-line-quasar comparison across radio-loud, radio-quiet, and pure subsamples, making clear that the apparent WLQ difference is limited by small-number uncertainties rather than a significant demographic excess.
Figure 6. This is the key diagnostic for the paper's BAL conclusion, showing that BAL quasars avoid the extreme radio-loud tail and that C IV absorption strength does not significantly track radio loudness.
Figure 10. The composite-spectrum comparison provides the strongest visual synthesis of the UV result: residuals between radio-detected versus non-detected and radio-loud versus radio-quiet stacks remain within 3σ, supporting broadly similar rest-UV spectral properties.

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2609.22449v1

LoTSS of dual AGN: enhanced detectability and prospects for a systematic search

Q. D'Amato, F. Mannucci, E. De Rubeis, I. Prandoni, A. De Rosa, M. Scialpi, M. Kunert-Bajraszewska, A. Janiuk, A. Krauze, L. Battistini, E. Bertola, C. Bracci, A. Chakraborty, M. Ceci, C. Cicone, G. Cresci, A. Marconi, C. Marconcini, E. Nardini, M. Parvatikar, A. Peca, K. Rubinur, P. Severgnini, C. Spingola, L. Ulivi, G. Venturi, C. Vignali, M. V. Zanchettin

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D’Amato et al. test whether sub-arcsecond 144 MHz LOFAR imaging can identify and characterize kpc-scale dual AGN, cross-matching 92 spectroscopically confirmed systems at z > 0.3 and reprocessing international-LOFAR data for three targets at 0.59 < z < 2.39. The pilot resolves both nuclei in J1120+6711 at z = 1.49 at >5σ, making it among the highest-redshift and faintest radio-detected dual AGN, while brightness temperatures show that even sub-mJy low-frequency emission can be AGN-powered. Only one nucleus is detected in each of J0930+4614 and J1643+3156; in the latter, the compact steep-spectrum morphology is attributed to jet–ISM interaction rather than the companion. Across the parent sample, LoTSS detects about 24% of dual AGN versus 9–10% of matched single AGN, positioning iLoTSS-like imaging as a dust-unbiased route toward systematic dual-AGN searches and SKA-era samples.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This is the core observational result: 0.3-arcsec 144 MHz ILT maps show both radio AGN in J1120+6711 while marking the undetected companions in J0930+4614 and J1643+3156. It directly conveys both the demonstrable resolving power for a z = 1.49 dual detection and the incompleteness implied by single-component detections.
Figure 3. The component-by-component radio spectra of J1643+3156 provide the physical diagnostic behind the paper’s interpretation of this system. They show how the new 144 MHz constraints distinguish core and hotspot behavior and support jet–ISM interaction, rather than the companion galaxy, as the origin of its complex radio morphology.
Figure 4. This synthesis figure connects the pilot to survey-scale prospects by comparing simulated dual-AGN surface densities with expected 144 MHz and 1.4 GHz flux densities and LoTSS/SKA detection limits. It makes clear why sensitive, wide-area low-frequency imaging can turn individual dual-AGN detections into a statistically useful census.