Weekly archive
LRDigestWeekly digests of little red dots and JWST-selected AGN papers, with curated reading notes and archive pages.
654 indexed papers · 430 research notes
![Figure 4 from Search for High-Ionization Nebular Emission (SHINE). I. A Systematically Selected [Ne V] Sample at z > 3 with JWST/NIRSpec PRISM](/lrdigest/research/figures/2609.27130v1/figure-4-1.png?v=1f796e8992092206)
SHINE identifies 25 luminous [Ne V] emitters at z=3.06–9.44 from >9,000 JWST/NIRSpec PRISM galaxies. Their hard-ionization lines favor accretion, but heterogeneous selection and incomplete diagnostic overlap preclude an intrinsic AGN-incidence measurement.
One-dimensional equilibrium models suggest that metal-enriched, hydrogen-burning supermassive stars can attain LRD-like cool photospheres through Fe-opacity-driven envelope inflation, while general-relativistic collapse could leave massive black-hole remnants. The proposed interpretation remains sensitive to atmospheric physics and formation assumptions.
VIPERS yields 14 compact, LRD-like sources at 0.5<z<1.75 selected through V-shaped photometric slopes and broad lines. Their inferred abundance declines sharply below z~1, while one unresolved X-ray source is consistent with a low-inclination, radiatively efficient disk.
RUBIES-EGS-9809 is a single, heavily obscured broad-line AGN host at z=5.7 whose resolved Balmer break and declining-SFR SED fit make it a quenching candidate, not a confirmed post-starburst. Outflow signatures make AGN feedback plausible but unproven.
This strategic report argues that Lynx-class subarcsecond, high-throughput X-ray imaging spectroscopy would test why JWST little red dots are X-ray weak, while simulations illustrate broader gains for feedback, accretion, and circumgalactic-gas studies.
Ighina et al. construct an eRASS:1-selected sample of extreme radio quasars by cross-matching eROSITA X-ray sources with RACS radio detections and DELVE optical/NIR dropout candidates, then spectroscopically following up 46 of 68 candidates. They confirm 39 quasars at z>3.5, including 14 new z>4 radio quasars, increasing the population above the same flux limits and area by about 65%. Their X-ray-to-optical and radio-loudness diagnostics identify a predominantly blazar-like subset, whose cumulative z>4 counts agree reasonably well with a fractional IC/CMB X-ray-enhancement model. The resulting uniformly selected sample provides a stronger basis for testing early jetted-SMBH growth and relativistic-jet evolution, although the redshift distribution remains affected by incomplete spectroscopy and blazar-classification choices.
Using a Soltan-normalized black-hole accretion history and a gas-dynamical upper envelope, the authors find black-hole horizons dominate cosmic entropy production but operate 4–7 dex below their proposed maximum at z=4–12.
XRISM/Resolve spectroscopy of the z=0.297 quasar cluster H1821+643 measures unusually broad ICM Fe XXV lines, implying substantial non-thermal motions on 20–100 kpc scales. The authors interpret these motions as quasar-feedback coupling, but resonance scattering and sloshing remain relevant alternatives.
XMM J130514.64-493311.27 is a soft, recurrent off-nuclear X-ray transient in NGC 4945. Its 2022 XMM-Newton luminosity of about 2.3×10^38 erg s^-1 and disk-like spectrum favor an X-ray binary, while the compact object remains unresolved.
Chandra and Keck/DEIMOS observations identify two obscured, broad-line AGN in the interacting Green Pea system J1622+3521, separated by 8.4 kpc. The authors therefore report a confirmed dual AGN in a compact low-mass Green Pea environment.
Using X-ray spectra of the single nearby, long-quenched galaxy KUG 1208+386, the authors report a ≈0.07c nuclear ultra-fast outflow. Its ≥3σ trial-corrected line evidence makes feedback in a quiescent host plausible, but not yet a demonstrated maintenance mechanism.
In one EIGER/J1030 field, five X-ray-undetected broad-line candidates imply an LRD density at z≈2.4 consistent with no decline from z≈7 above Lbol=3×10^44 erg s−1, but the large counting uncertainty and small sample preclude a precise evolutionary constraint.
SDSS color selection identifies ~1,300 low-redshift “LoRD” quasars whose V-shaped subset resembles LRD spectral energy distributions, but host contamination, unresolved morphology, and weak high-z X-ray limits prevent establishing them as a uniformly faithful analog population.
Monte Carlo torus calculations predict that metal-poor, Compton-thick AGN can transmit more X-ray flux than solar-metallicity counterparts, potentially aiding z≳10 detection. The result is model-based: geometry, viewing angle, abundance pattern, and cold-gas assumptions remain consequential.
In 36 GOODS LRDs/LBDs at z=2.26–7.89, the authors find AGN-like narrow-line excitation, extreme X-ray weakness, and LRD Lyα excess with a broad component resembling Hα. They argue against completely enclosing cocoon geometries, while retaining obscured-LBD interpretations.
This modeling paper interprets little red dots as high-inclination, hyper-Eddington SMBHs analogous to SS 433: self-shielding in a puffed-up disk can produce cool red continua and Balmer breaks, while making several inclination-dependent predictions testable.
Swift eclipse monitoring of ESO 362-G18 uses time-resolved absorption changes to constrain an X-ray source within ~35 Rg. The authors infer a structured cloud and a soft-excess region ~50% larger than, yet overlapping, the hot corona.
KOOLS-IFU maps of NGC 6552 find broad [O III] emission declining with radius but no significant full-sample association between local kinematics and [O III]/Hβ excitation, favoring spatial dynamical structure over a detected excitation–kinematics coupling.
Radiative-transfer models and three illustrative spectra support a hypothesis that little blue dots are lower-column, gas-cocooned AGN related to little red dots. Balmer-jump offsets are suggestive, but population-level fitting and discriminating tests remain outstanding.
Using X-ray spectra and infrared-informed absorption priors, the authors infer that Compton-thick AGN comprise 17% of AGN at z=3–6. The revision sharply reduces candidate classifications, but supports no significant redshift evolution in this fraction.
Across a large SDSS–eROSITA quasar sample, bolometric luminosity scales nearly linearly with virial black-hole mass while hard X-rays rise more slowly. The authors argue this disfavors classical Bondi feeding and favors CCA, but redshift covariances and JWST line-based systematics limit interpretation.
This theoretical magnetized black-hole-envelope model links cool LRD continua, broad-line shapes, and weak X-rays to super-Eddington spherical inflow onto a rotating envelope, but its quantitative success remains conditional on assumed envelope structure, opacity, magnetism, and line-scattering physics.
Using simulation-based inference on a synthetic local AGN population, the authors find an intrinsic Compton-thick fraction of 40±3%. Their radiation-regulated geometry broadly reproduces several X-ray observables, but depends materially on fixed, simplified broad-line-region and torus assumptions.
Sirocco cocoon models suggest that current LRD X-ray non-detections require both moderately enriched, Compton-thick gas and intrinsically X-ray-weak/soft AGN emission. The inference is conditional on assumed intrinsic SEDs, metallicities, columns, and redshift-dependent observing bandpasses.
eROSITA-triggered monitoring of HE 1237-2252/J1240−2309 links a changing-look transition to intrinsic accretion-rate recovery and an evolving two-component Balmer-line profile. A diskline-like component strengthens with UV flux, while the proposed corona/illumination mechanism remains interpretive.
Across four optical and three X-ray epochs, J0413-0050 changed from broad Balmer emission in 2004 to an Hβ-free 2021 state and back to broad plus narrow Hβ in 2023. The authors favor changing accretion over obscuration, but X-ray column density is unconstrained.
After image decomposition and host-only SED fitting, 36 NIRCam-selected NEP-TDF AGN candidates separate into a likely AGN “branch” and an ambiguous, largely early-type “bridge” near quenching; the reported SFR–AGN-fraction trend is weakly explanatory.
For the single $M_\star\sim10^{10}\,M_\odot$ host GAMA 376183, NuSTAR and multiwavelength data support a heavily obscured, rapidly accreting AGN in a disturbed system; the proposed merger-triggered starburst/accretion connection remains suggestive rather than demonstrated.
A semi-numerical PBH-seeded AGN model predicts that PBH X-ray heating makes cosmic-dawn 21-cm absorption shallower and suppresses power, with outcomes strongly dependent on the assumed PBH mass function and X-ray escape fraction.
XRISM Resolve spectroscopy of the crowded Galactic-centre field isolates narrow iron-line emission attributed to the black-hole candidate MAXI J1744-294, including static highly ionized gas and atypical features consistent with blueshifted material, though plasma origin and background systematics remain unresolved.
A reanalysis of UHZ1’s full Chandra exposure and new MIRI non-detections reduces the evidence for its proposed luminous, Compton-thick direct-collapse black hole: the X-ray excess is marginal and non-persistent, while infrared limits exclude the originally inferred luminosity scale.
In a 140 deg² eROSITA field, the authors identify eight z=0.3–0.8/1 quasars with inferred M•/M⋆>5%. Their abundance supports recurrent black-hole/host offsets among rapidly accreting AGN, but single-epoch masses and often upper-limited host masses temper the conclusion.
Two z≈0.7 compact dwarfs combine blue, burst-dominated UV–optical emission with a MIRI hot-dust excess. SED-inferred AGN luminosities imply candidate black holes disproportionately massive for ≈10^7 M⊙ hosts, but masses depend strongly on the assumed Eddington ratio.
A radio-loud quasar at z=1.715 has a ∼10,000 K curved UV continuum and broad lines, making it a plausible—but unconfirmed—low-redshift analogue of an LRD-to-quasar transition.
High-redshift LRDs and JWST-selected broad-line AGN are X-ray weak relative to broad Hα, plausibly resembling highly accreting local systems; however, predominantly upper-limit-based X-ray constraints leave intrinsic coronal suppression and obscuration unresolved.
Joint modelling of broad lines and Chandra non-detections for 14 JWST high-redshift broad-line AGNs favors low-mass, highly super-Eddington black holes with over-cooled coronæ over massive, weakly accreting alternatives, but the inference remains model-dependent and bimodal.
Using X-ray non-detections of Little Red Dots, the authors model collisionally formed black-hole seeds and argue that heavy-seed evolutionary tracks can meet flux limits, conditional on degenerate assumptions about structural evolution, accretion, metallicity, and absorption.
Among 10 UV-selected, extremely luminous radio-quiet non-BAL quasars with confirmed C IV outflows, only two are X-ray weak. A possible X-ray-weakness/outflow link appears only above 3000 km s⁻¹ and is tentative (~2σ).
For 194 X-ray AGN at z<1.5 in GOODS, the authors find predominantly obscured SEDs and mainly disk-dominated hosts. A statistically distinct, faint obscured SED class is more spheroid-rich, while the observed interaction fraction does not establish triggering causality.
A two-object JWST comparison finds that a prototypical Little Red Dot and Little Blue Dot share broad, non-Gaussian Balmer emission, weak hot dust, and X-ray weakness, but differ sharply in helium emission and Balmer absorption.
JWST/NIRSpec spectroscopy of 16 ALMA-selected HUDF faint SMGs finds dusty, massive z=1–4 galaxies with mostly obscured AGN classifications, yet star-formation, metallicity, and bulk-ISM properties broadly consistent with comparable high-redshift star-forming populations.
In local merging (U)LIRGs, 230-GHz continuum combined with X-ray luminosity and IR-based SFR can conservatively separate star-formation-compatible systems from candidate obscured AGN; the authors identify one confirmed AGN and two strong candidates, but calibration remains preliminary.
A radiation-hydrodynamic direct-collapse black-hole model can fit one prototypical Little Red Dot spectrum with low residuals while producing Compton-thick obscuration. The result is a model-based explanation, not yet a population-level demonstration that all LRDs are DCBHs.
A single z=3.28 compact “X-Ray Dot” combines Little Red Dot-like optical spectra with luminous hard X-rays. The authors favor, but do not establish, a transitional gas-envelope geometry over unusual nuclear dust.
This mini-review argues that little red dots are probably heterogeneous: broad Balmer lines and compact, V-shaped SEDs support accretion in some, whereas pervasive multiwavelength non-detections and viable stellar fits prevent a population-wide AGN identification.
The authors propose that LRDs are transient, Compton-thick inflows within fuzzy-dark-matter soliton cores. Their size-and-column arguments favor boson masses of a few ×10^-22 eV, but the mechanism remains an analytic, idealized-merger scenario requiring radiation-hydrodynamic tests.
New Chandra coverage makes the X-ray census nearly complete for the brightest known z~7 quasars, finding broadly familiar UV–X-ray scaling but substantial scatter, a tentative wind–SED association, and a soft stacked X-ray spectrum consistent with high accretion rates.
Reports two COSMOS LRDs—Forge I (z=2.868) and Forge II (z=2.925)—whose V-shaped UV–optical SEDs, compact morphologies, and broad Paschen/He I lines meet LRD criteria. Unlike typical LRDs, they show strong X-ray, radio, and mid-IR emission, moderate X-ray obscuration, a 6.4 keV Fe K line in Forge II, and unusually large year-scale X-ray variability while UV broad lines remain weak/absent. The spectra reveal strong He I absorption in both and rare Pa absorption in Forge II, indicating dense, low-ionization gas with mixed inflow/outflow kinematics as the envelope thins. Authors argue these hybrids are LRDs in transition, with dispersing dense gas and an emerging dust torus, implying some LRDs evolve into normal AGN/quasars.
Two z~3 X-ray AGNs with He I λ10830 absorption indicate dense, broad-line-region-scale circumnuclear gas, but their contrasting obscuration, accretion rates, and outflow signatures provide only a two-object, model-dependent case for an evolutionary sequence.
A 184-object COSMOS sample selected through [Ne V] or C IV combines X-ray–radio SED fitting with Simba analogues. The authors infer obscured, high-accretion transitional populations, with [Ne V] hosts pre-quenching and C IV hosts more often quenched.
A 280 ks Chandra study identifies the z=3.631 Hot DOG W0410-09 as a Compton-thick, intrinsically luminous quasar and finds tentative stacked Fe Kα evidence for obscured AGN among nearby Lyα emitters, but not individual LAE detections.
ID830 is a z=3.4351 radio-loud quasar with extreme, steep X-ray emission and a UV-based super-Eddington estimate. The authors interpret its X-ray excess as corona-plus-jet emission during a possible post-burst transition, not a demonstrated evolutionary state.
For 87 CEERS X-ray AGN at 0.1<z<4, JWST F115W Sérsic+PSF decompositions recover host and AGN magnitudes more robustly than morphology: Sérsic index and effective radius depend strongly on fitting code and are mutually covariant.
A joint luminosity-function and escape-fraction model attributes 31–75% of z>5 ionizing photons to AGN, but the result depends on assumed galaxy escape fractions and an outflow-based AGN LyC-escape prescription available here only in the abstract.
For 88 X-ray-selected CEERS AGN at 0.7≤z≤3.5, simultaneous central and integrated JWST/archival SED fitting yields tighter torus constraints. Among 66 luminous sources, torus covering fraction peaks near 0.25 and is not statistically distinguishable from a luminosity-matched local comparison.
Joint NuSTAR–XMM-Newton spectroscopy of the 60-source NEP hard-X-ray catalog yields an observed Compton-thick fraction of 0.13^{+0.15}_{-0.04}; correcting absorption bias raises the inferred underlying fraction to 0.32^{+0.23}_{-0.08}.
XRISM/Resolve resolves a Compton-thick, warm-obscured yet sub-Eddington GRS 1915+105 into narrow photoionized emission zones, supporting outer-disk occultation. A warped, precessing disk is favored over inner-disk thickening, but residual spectral structure and geometry remain unresolved.
A nuclear-star-cluster model suggests that dense, gas-fed clusters can grow an intermediate-mass seed into an LRD-scale massive black hole by z~5, while predicting tidal disruptions more frequently than stellar-mass-BH captures at z=4–6.
JWST/NIRCam morphologies and matched controls indicate that obscured, Seyfert-luminosity AGN hosts at cosmic noon are more disturbed than inactive galaxies. The authors interpret the combined trends with column density and X-ray/IR selection as a major-merger evolutionary branch.
In XMM-LSS, mass-controlled IR-selected AGN incidence is higher in dense environments at z>1.2 but higher in sparse environments at z<1.2; X-ray AGN show no significant trend. Bootstrap resampling supports the IR reversal, not a causal triggering mechanism.