654 indexed papers · 430 research notes

Research archive

2025-08-29 · 2508.21678v1

Investigating Little Red Dots with UV Excess: Are They the High-Redshift Siblings of Blue Hot DOGs?

Lulu Bao, Chao-Wei Tsai, Jingwen Wu, et al.

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The authors stack NIRCam+MIRI photometry for 326 “V-shape” LRDs (from Akins24 and Kokorev24) and compare their UV–NIR SEDs to median-stacked Blue-excess Hot DOGs (BHDs) to test the analog hypothesis. Despite superficially similar “V-shapes,” LRDs turn over at shorter wavelengths, have much bluer rest-IR continua, show F1800W non-detections in stacks, and require far lower dust attenuation in SED fits—indicating little or no AGN-heated hot dust. They also argue the UV excess in LRDs is unlikely to be scattered AGN light, and note compact morphologies plus lower X-ray detection frequencies. Bottom line: LRDs are not simply high‑z siblings of BHDs, pointing to a distinct early SMBH growth pathway from the super‑Eddington, merger-driven Hot DOG phase.

LRD v-shaped SED obscured AGN demographics X-ray high-z

2025-08-27 · 2508.20177v1

MEGA: Spectrophotometric SED Fitting of Little Red Dots Detected in JWST MIRI

Kaila Ronayne, Casey Papovich, Allison Kirkpatrick, et al.

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MEGA fits JWST/NIRCam+NIRSpec+MIRI SEDs for eight spectroscopically confirmed Little Red Dots at z=5.1–8.7 using CIGALE and Prospector across star-forming, AGN-dominated, and composite scenarios. By BIC, six of eight prefer AGN-dominated solutions, consistent with red F150W–F444W > 1 but flat F444W–F770W and −1.0 < F1000W–F1500W < 1.1 colors that imply weak hot dust. Two Balmer-break LRDs with broad Hα are matched by hot, dense-gas (log T=5–5.7; log n=9–11) plus an added 800–1400 K thermal component, with total Lbol/L_sun < 10^12 and consistency with far-IR/radio limits. However, no single template reproduces all observables—the dense-gas fits miss the rest-UV and narrow [O III]—arguing for non-standard gas conditions and mixed AGN–star-formation.

LRD spectroscopy broad Balmer high-z

2025-08-25 · 2508.18358v1

The Missing Hard Photons of Little Red Dots: Their Incident Ionizing Spectra Resemble Massive Stars

Bingjie Wang, Joel Leja, Harley Katz, et al.

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Using recombination lines rather than continuum, the authors analyze uniformly selected RUBIES LRDs plus an 8 hr G395M spectrum of RUBIES‑EGS‑49140 to infer the incident ionizing spectra. They find a strong tension: very large Hα equivalent widths demand abundant H-ionizing photons, yet HeII is only marginally detected with HeII/Hβ ~10^-2, far below local AGN, implying an unusually soft spectrum missing hard photons. Cloudy modeling rules out standard AGN accretion-disk SEDs and favors soft, star-like ionizing fields (e.g., cold disks or AGN+stars composites) and/or high gas/dust optical depths, with HeII remaining an optically thin, robust tracer even in dense neutral hydrogen “black-hole star” envelopes. The HeII-based diagnostic reframes the LRD central-engine debate by highlighting missing hard photons and incident spectra that resemble massive stars.

LRD spectroscopy stellar envelope high-z

2025-08-22 · 2508.16795v1

On the Variability Features of Active Galactic Nuclei in Little Red Dots

Shuying Zhou, Mouyuan Sun, Zijian Zhang, et al.

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Applies the CHAR (corona-heated disk reprocessing) model to the Tee et al. (2025) 22-object LRD sample to interpret their multi-epoch photometry. Finds that the measured |Δm| is dominated by photometric uncertainties; within CHAR the non-detections are consistent with either AGN light fractions ≲30% or intrinsically luminous AGN whose fractional variability is small. Simulations specify what it would take to break this degeneracy: ≈200 LRDs, two epochs separated by ≥2 years (observed frame), and σ_phot ≤0.07 mag. If variability still fails to appear, it would point to accretion modes unlike those of low‑z quasars, offering independent constraints on what powers LRDs.

LRD variability v-shaped SED simulation high-z

2025-08-20 · 2508.14897v1

Little Red Dots as Direct-collapse Black Hole Nurseries

Elia Cenci, Melanie Habouzit

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Preliminary MELIORA cosmological simulations implement a direct-collapse BH formation model that tracks Lyman–Werner irradiation and halo inflow rates to test whether newborn heavy seeds can resemble Little Red Dots. The simulated population of newly formed DCBHs drops sharply at z<6 as inflows wane, mirroring the observed emergence-and-decline trend of LRDs. DCBH birth coincides with a strong gas-compaction event and a short, bright AGN phase lasting ~200 Myr, after which the first Pop III stars appear and the AGN fades. If LRDs trace this nursery phase, their weak X-ray and hot-dust signatures follow naturally from the scenario.

LRD BH seeds simulation high-z X-ray

2025-08-19 · 2508.14155v1

Little Red Dots and their Progenitors from Direct Collapse Black Holes

Junehyoung Jeon, Boyuan Liu, Volker Bromm, et al.

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Using the A-SLOTH semi-analytic framework, the authors generate a DCBH-seeded SMBH population and benchmark it against Little Red Dot (LRD) demographics and spectra. Heavy (DCBH) seeds reproduce the observed LRD BH mass functions, number densities, and host-halo trends better than stellar-remnant seeds. For the most extreme early LRDs (e.g., MoM-BH*-1), DCBH scenarios with either strong dust attenuation or dense, dust-free gas can match the distinctive V-shaped, Balmer-break–dominated SEDs, whereas even super-Eddington growth on light seeds cannot. The work points to gas metallicity as a crucial observable, beyond BH-to-stellar mass ratios, to pin down LRD progenitors.

LRD BH seeds simulation demographics v-shaped SED high-z

2025-08-19 · 2508.13541v1

Little Red reionization factories

Fan Zhang

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Proposes Little Red Dots as “reionization factories,” where a Weyl-curvature–driven Cosmic Tide funnels intergalactic HI into colliding streams that shock, compress, and trigger rapid starbursts whose LyC reionizes hydrogen. In this picture, hot HII escapes along interstitial directions, so reionization proceeds via outflowing plasma rather than requiring extreme photon escape fractions. The model predicts a gas-dominated rest‑optical continuum—HII bremsstrahlung with a minimum‑timescale red cutoff and an IR rollover from opacity—while the UV is stellar, naturally producing strong Balmer breaks. It also anticipates narrow+broad Balmer components and slightly shifted Balmer absorption from bulk‑moving n=2 HI, with a proof‑of‑concept SED fit to J1025+1402; the scenario is explicitly speculative.

LRD reionization nebular continuum high-z

2025-08-12 · 2508.08768v1

Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots

Seok-Jun Chang, Max Gronke, Jorryt Matthee, et al.

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The authors run 3D Monte Carlo radiative transfer to test how resonance, Raman, and Thomson scattering sculpt Balmer lines in Little Red Dots. Resonance scattering in an n=2–populated H I medium drives strong departures from Case B and distinct Hα vs Hβ shapes, but Hβ is funneled into Paα, preventing broad Hβ wings. Raman scattering of higher Lyman-series emission can explain Hα/Hβ wing-width ratios ≳1.28, whereas Ramanization of a UV continuum is disfavored by the near-constant FWHM across transitions. Thomson scattering with Te≈10^4 K and electron column ≈10^24 cm−2 reproduces the ≳1000 km s−1 wings and implies virial BH masses can be overestimated by ≳10 if widths are taken at face value.

LRD broad Balmer simulation overmassive BH spectroscopy

2025-08-02 · 2508.01372v1

A Nitrogen-rich AGN Powering a Large Ionizing Bubble at z=8.63

Takahiro Morishita, Massimo Stiavelli, Charlotte A. Mason, et al.

New NIRSpec/MSA G140H/F070LP data reveal broad Lyα in CANUCS-LRD-z8.6 (z=8.63) centered near systemic (FWHM 1540±260 km/s), implying transmission through a large reionized region. Simple Strömgren modeling of the line shape yields an ionized-bubble radius Rb=1.5^{+0.3}_{-0.2} pMpc and a Lyα escape fraction fesc=11±3%. The intrinsic width is even broader (≈2200±280 km/s), consistent with a BLR in a low-luminosity AGN, while high N IV]/C IV and N IV]/O III] ratios from PRISM indicate nitrogen enrichment. A mild local overdensity (δ≈1.8) suggests neighboring galaxies may help sustain the bubble, linking this LRD to the emerging class of nitrogen-rich systems like GN-z11 and GHZ2/GLASSz12.

LRD broad-line AGN reionization spectroscopy high-z

2025-08-01 · 2508.00774v1

A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes

Saiyang Zhang, Boyuan Liu, Volker Bromm

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High-resolution hydrodynamics around ∼10^6 M⊙ primordial black holes show that accretion-driven LW fields plus strong baryon–DM streaming (v_bχ ≳ 0.8 σ_bχ) push gas onto an atomic-cooling track and trigger collapse in the PBH wake. The collapsing clouds sustain inflow rates ≳0.01–0.1 M⊙ yr⁻¹, enabling ∼10^5 M⊙ supermassive stars that rapidly form direct-collapse BHs at z ∼ 20–10. These secondary DCBHs pair with the primary PBH to yield in-situ SMBH binaries with initial q ≈ O(0.1) at ∼10 pc separations. The channel predicts compact, LRD-like sources and low-frequency GW emitters accessible to JWST/ALMA and LISA/TianQin.

BH seeds simulation high-z stellar envelope LRD

2025-07-31 · 2508.00057v1

Discovery of a Little Red Dot candidate at $z\gtrsim10$ in COSMOS-Web based on MIRI-NIRCam selection

Takumi S. Tanaka, Hollis B. Akins, Yuichi Harikane, et al.

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Using COSMOS-Web’s joint NIRCam–MIRI imaging, the authors conduct the first targeted search for little red dots beyond z≈10, leveraging F770W to isolate the V‑shaped SED signature and cull Balmer‑break contaminants. They uncover one robust source, CW-LRD-z10, with zphot=10.5(+0.7/−0.6), MUV=−19.9(+0.1/−0.2), compact morphology, a clear V‑shaped SED, and an F115W non‑detection consistent with an LRD at z∼10. From this single detection they infer a number density at MUV≈−20 of 1.2(+2.7/−1.0)×10⁻⁶ Mpc⁻³ mag⁻¹, implying the LRD fraction rises with redshift to ≈3% at z∼10. If confirmed, this points to LRDs as a common early population potentially tied to the first SMBH growth; deep spectroscopy is still required to secure the redshift and nature of CW-LRD-z10.

LRD v-shaped SED high-z demographics compact red

2025-07-31 · 2507.23774v1

Lord of LRDs: Insights into a "Little Red Dot" with a low-ionization spectrum at z = 0.1

Xihan Ji, Francesco D'Eugenio, Ignas Juodžbalis, et al.

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A nearby LRD analog is uncovered: the broad-line AGN SDSS J102530.29+140207.3 at z=0.1 shows the hallmark V-shaped SED, broad Balmer emission (FWHM 1000–2000 km/s), and deep Balmer absorption. New GTC optical spectra reveal a G–K-giant-like continuum with a clear CH G-band and unusually deep low-ionization absorption, plus a series of [Fe II] emission lines; similar [Fe II] features are identified in a JWST-selected LRD at z=2.26. Multi-epoch data show small but significant Hα variability, and NuSTAR confirms extreme X-ray weakness consistent with Compton-thick obscuration (NH>10^24 cm^-2). Together these point to a dense, complex nuclear environment that reproduces LRD hallmarks locally and informs early black-hole growth, though the strength of the ionic/atomic/molecular absorptions remains challenging for standard stellar/AGN models.

LRD v-shaped SED broad Balmer obscured AGN X-ray low-z

2025-07-29 · 2507.22014v1

Little Red Dots as self-gravitating discs accreting on supermassive stars: Spectral appearance and formation pathway of the progenitors to direct collapse black holes

Lorenz Zwick, Christopher Tiede, Lucio Mayer

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Models little red dots as supermassive stars fed by massive self‑gravitating discs assembled in gas‑rich major mergers, reproducing the V‑shaped SED as two blackbodies and attributing Balmer broadening to disc rotation—without invoking extra AGN, stellar, or dust components. MCMC fits to two representative LRDs (J0647‑1045 and COS‑756434) yield sub‑Eddington disc accretion and SMS masses of a few ×10^6 Msun with physically motivated parameters. The framework predicts a luminosity cut‑off of order few ×10^44 erg/s and ties the observed redshift distribution of LRDs to merger rates, matching current trends. Acknowledged caveat: reproducing the absolute abundance of LRDs remains challenging, though the fits are robust to observed diversity.

LRD stellar envelope BH seeds v-shaped SED broad Balmer simulation

2025-07-28 · 2507.20684v1

A deep dive down the broad-line region: permitted OI, CaII and FeII emission in an AGN Little Red Dot at z=5.3

Roberta Tripodi, Maruša Bradač, Francesco D'Eugenio, et al.

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JWST/NIRCam imaging and NIRSpec prism spectroscopy of the Bullet‑cluster LRD Bz5.3 (zspec=5.2907) reveal broad Balmer emission plus strong low‑ionization Fe II, O I, and Ca II triplet lines, confirming a bona fide BLR around an accreting SMBH. The work reports the first high‑z detection of the O I λ1304 bump (O I+Si II), alongside prominent O I λ8446 and Ca II λλ8498,8542,8662. A markedly low O I λ1304/λ8446 photon ratio (0.1–0.3) implies internal dust with AV≈0.4–1.0 and points to Lyβ fluorescence as the dominant excitation, consistent with high EW O I λ8446 and weak O I λ7774. Photoionization modeling of O I and Ca II favors multiple BLR gas phases with distinct densities/ionization states, supporting a stratified BLR at early times.

LRD broad-line AGN broad Balmer spectroscopy high-z

2025-07-23 · 2507.17833v1

Not-quite-primordial black holes seeded by cosmic string loops

Bryce Cyr

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This work builds an improved, unified framework for the halo mass function seeded by cosmic string loops, treating arbitrary loop-velocity distributions and capturing both spherical and filamentary growth. From this mass function, it isolates halos that meet direct-collapse conditions at high redshift, producing black-hole seeds of ~10^4–10^5 Msun. For reasonable string parameters, the predicted seed abundance reproduces the observed number density of JWST’s Little Red Dots, offering a non-Gaussian small-scale route to early SMBH growth. Because loop formation lacks large acoustic waves, the scenario avoids CMB spectral-distortion bounds, and a velocity–tension phase diagram (including fragmentation into “beads”) clarifies where this channel dominates.

BH seeds simulation LRD high-z demographics

2025-07-23 · 2507.17738v1

Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs

Pierluigi Rinaldi, George H. Rieke, Zihao Wu, et al.

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The authors present WISEA J123635.56+621424.2 (“the Saguaro”) at z=2.0145 in GOODS‑North as an LRD analog: a compact, LRD‑like nucleus with a face‑on spiral host and a clear V‑shaped nuclear SED from NIRSpec. Redshifting the system to z≈7 renders the host undetectable via surface‑brightness dimming, reproducing a canonical LRD appearance and implying many high‑z LRDs could be visible galactic nuclei embedded in extended hosts. A stack of rest‑UV images for 99 photometrically selected LRDs reveals faint diffuse emission and mild radial growth with redshift, consistent with galaxy size evolution. A simple analytic model shows surface‑brightness dimming alone can explain the compact morphology, arguing LRDs are a short‑lived, AGN‑dominated phase rather than a distinct population.

LRD v-shaped SED JWST AGN demographics

2025-07-21 · 2507.15556v1

Signatures of Exploding Supermassive PopIII Stars at High Redshift in JWST, EUCLID and Roman Space Telescope

Cédric Jockel, Kyohei Kawaguchi, Sho Fujibayashi, et al.

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Semi-analytic models, anchored to stellar-evolution and GR collapse simulations, follow ejecta–CSM shocks from exploding supermassive Pop III stars to predict light curves, spectra, and photometry. The events peak at ~10^45–10^47 erg/s and last 10–200 yr in the source frame (observed 250–3000 yr), yielding quasi-persistent variability indistinguishable from little red dots/AGN on 0.5–9(1+z) yr baselines. Bright explosions should be detectable in long-wavelength JWST filters to z≤20 at 24–26 mag, with pulsating SMSs to z≤15; Euclid and Roman reach z<11–12. Deep fields could constrain the event rate to ~10^-11 Mpc^-3 yr^-1 and yield several hundred (Euclid) to dozens (Roman) detections, directly testing heavy-seed SMBH pathways.

BH seeds simulation high-z variability LRD

2025-07-16 · 2507.12618v1

Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots

Devesh Nandal, Abraham Loeb

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First-principles synthetic spectra for non-rotating, metal-free supermassive stars (up to 10^6 M⊙) are used to test whether LRDs are direct photospheres of SMSs. The model’s luminosity at 4050 Å (Lλ ≈ 1.7×10^44 erg s^-1 μm^-1) and NLTE physics reproduce hallmark LRD traits—a V-shaped Balmer break and strong Hβ emission with other Balmer lines in absorption—with wind/macroturbulent broadening matching observed profiles. Quantitative fits to sources at z=7.76 and z=3.55 include an Hβ width match for MoM‑BH*-1 to within 4%, offering a self-consistent alternative to multi-component obscured AGN. A luminosity-dependent visibility window of ~10^4 yr for the brightest systems and 10^5–10^6 yr for objects 1–2 dex fainter implies LRDs may capture brief, pre-collapse stages of SMBH progenitors.

LRD stellar envelope BH seeds v-shaped SED broad Balmer high-z

2025-07-14 · 2507.10659v1

The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes

Xiaojing Lin, Xiaohui Fan, Zheng Cai, et al.

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Reports three SDSS-selected local little red dots at z=0.1–0.2 with LBT/MODS and Magellan/FIRE follow-up, showing the same hallmarks as high‑z LRDs: compact morphologies, V‑shaped UV–optical SEDs with declining NIR continua, broad H/He lines, full Balmer+Paschen series, and minimal variability. All display blue‑shifted He I absorption; two show Hα and Na D absorption, and two have abundant narrow [Fe II]; J1025+1402 (The Egg) further exhibits extreme Na D, K I, and Ca II triplet absorption consistent with a cool (~5000 K), metal‑enriched envelope. Line diagnostics point to AGN‑powered, metal‑poor narrow lines with little dust, very high‑density inner regions for the broad lines (or unusual dust), and [Fe II] from dense gas between them; two targets are X‑ray non‑detections and WISE photometry implies only weak dust (T ~10^2–10^3 K). The authors propose a largely thermalized cool‑gas envelope plus an extended, high‑density outflow to unify these features, positioning local LRDs as resolvable analogs of early BH growth.

LRD low-z v-shaped SED broad Balmer stellar envelope outflows

2025-07-12 · 2507.09085v1

Little Red Dots As Late-stage Quasi-stars

Mitchell C. Begelman, Jason Dexter

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Begelman and Dexter propose that JWST “Little Red Dots” are late-stage quasi-stars: black holes embedded in massive envelopes accreting at super‑Eddington rates once the BH exceeds ~10% of the total mass. In this regime the models predict mass‑insensitive global properties, yielding reddish continua with a pronounced Balmer break and Balmer lines broadened primarily by electron scattering rather than Doppler motions. The enormous electron columns naturally quench X‑rays, while BHs grow roughly linearly in time; late-stage objects with MBH ≳10^6 Msun should dominate the quasi-star population. Given lifetimes of only tens of Myr yet high observed LRD number densities, the authors argue most SMBHs likely pass through this quasi‑star/LRD phase.

LRD stellar envelope super-Eddington broad Balmer X-ray

2025-07-11 · 2507.08929v1

Ruling out dominant electron scattering in Little Red Dots' Rosetta Stone using multiple hydrogen lines

Matilde Brazzini, Francesco D'Eugenio, Roberto Maiolino, et al.

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Targets the LRD “Rosetta Stone” GN-28074 (z=2.26) and tests whether broad Balmer/Paβ wings are dominated by wavelength-independent electron scattering. Using JWST/NIRSpec MSA medium-resolution data (∼1.7 hr), the authors compare Hα, Hβ, and Paβ profiles in velocity space and find mismatched wing shapes, contrary to the electron-scattering prediction of identical profiles. Joint fits with Gaussian BLR components plus exponential scattering wings cannot simultaneously match all three lines with physically plausible parameters. Result: dominant electron scattering around the BLR is ruled out for GN-28074, arguing against a universal systematic BH-mass overestimation in LRDs.

LRD broad Balmer spectroscopy

2025-07-09 · 2507.07190v1

The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion

Hanpu Liu, Yan-Fei Jiang, Eliot Quataert, et al.

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Semi-analytic atmospheres plus radiative-transfer show that super-Eddington flows can reproduce LRDs’ red rest-optical continua and Balmer breaks without dust or an external absorbing shell. A cool, low-density photosphere (ρ < 10^{-9} g cm^{-3}) creates a strong opacity jump at the Balmer limit, yielding a break even at T_eff ≈ 5000 K. Thin disks match the color only with a fine-tuned inner truncation giving T_eff ~ 5000 K, whereas a geometrically thick, quasi-spherical flow naturally produces T_eff ≈ 4000–6000 K largely insensitive to Ṁ (Hayashi-line-like). The resulting continua agree with current LRD spectra and motivate predictions for future super-Eddington simulations.

LRD super-Eddington broad Balmer

2025-07-09 · 2507.07171v1

Little Red Dots from Small-Scale Primordial Black Hole Clustering

Borui Zhang, Wei-Xiang Feng, Haipeng An

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Proposes LRD heavy seeds as runaway-merger products of primordial black holes initially clustered by small-scale long–short mode coupling. Monte Carlo solutions of the Smoluchowski equation yield merger timescales sufficient to assemble 10^5–10^8 Msun SMBHs within the first Gyr while evading CMB distortion limits. The scenario predicts a distinctive stochastic gravitational-wave background and high birth spins inherited from cluster tidal torques. Interpretation assumes LRDs host obscured AGN.

LRD BH seeds simulation high-z obscured AGN

2025-07-05 · 2507.04011v1

Investigating the Growth of Little Red Dot Descendants at z<4 with the JWST

Jean-Baptiste Billand, David Elbaz, Fabrizio Gentile, et al.

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Using CEERS imaging, the authors select z<4 “post-LRD” candidates by requiring a compact, very red core plus a blue star-forming envelope, then model inner/outskirts with stellar-only SED fits and single-Sérsic morphologies. The sample shows LRD-like cores with M* ~1e10 Msun, Σ* ~1e11 Msun kpc^-2, and compact sizes about 1 kpc below the size–mass relation, while adding an extended young component; their number density at z=3±0.5 (~10^-4.15 Mpc^-3) matches that of LRDs at 5<z<7, indicating an evolutionary link. Outskirts mass fraction and size increase toward lower redshift (≈250 pc at z=5 to ≈600 pc at z=3), as the core stays red/compact and the hallmark V-shaped SED fades, consistent with growth by cold accretion. This offers an explanation for the apparent decline of LRD counts at lower z, with the caveat that it assumes a single evolutionary path and stellar-only modeling.

LRD compact red v-shaped SED demographics

2025-07-04 · 2507.03230v1

Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter

M. Grant Roberts, Lila Braff, Aarna Garg, et al.

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Proposes ultra-strongly self-interacting dark matter (uSIDM) as a route to rapid gravothermal core collapse in early halos, yielding massive black hole seeds (≳10^5 Msun) by z≳5 that can power Little Red Dots. Builds a semi-analytic framework tracking halo evolution, collapse redshifts z_coll, and the SMBH mass function with stochastic growth via a log-normal Eddington ratio and finite duty cycle. Finds that uSIDM reproduces LRD abundance, compactness, and characteristic BH masses, with a z≈5 SMBH mass function matching LRD data and SIDM merger-tree results, especially at m_BH≳10^7 Msun. Implies LRDs could be incisive tracers of non-gravitational dark sector physics and that early SMBH assembly may depart from CDM expectations.

LRD BH seeds simulation high-z obscured AGN

2025-06-25 · 2506.20634v1

The VLA Frontier Fields Survey: A 6GHz High-resolution Radio Survey of Abell 2744

Esteban A. Orozco, Eric F. Jiménez-Andrade, Eric J. Murphy, et al.

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Ultra-deep 6 GHz VLA imaging of Abell 2744 (z=0.307) reaches ≈1 µJy beam−1 at 0.82″, yielding 93 detections, 46 with optical/NIR counterparts spanning z=0.15–3.55 (median z=0.93; median M⋆≈2.3×10^10 M⊙). Radio-inferred SFRs exceed UV–NIR estimates by roughly an order of magnitude, pointing to heavily obscured star formation missed by rest-UV/optical tracers. No individual radio counterparts are found for the z≈6 Little Red Dots; stacking sets a stringent 3σ limit of L6 GHz < 4.1×10^39 erg s−1. The survey also assembles 22 μ≳2 lensed systems, enabling sub-arcsecond probes of main-sequence galaxies at z∼1–2.

radio LRD high-z

2025-06-24 · 2506.19589v1

Black Holes in the Red-sequence Elliptical Galaxies at Redshifts $\sim 0.7-2.5$: Not Dark Energy Source but Remanants of Little Red Dots

Lei Lei, Ze-Fan Wang, Yi-Ying Wang, et al.

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Uses a JWST-selected set of very high‑z AGNs in red‑sequence ellipticals to test black‑hole cosmological coupling via the MBH–M* fundamental plane. The sample aligns with the local relation and yields a posterior on the coupling strength that rejects the “BHs as dark energy” scenario at >10σ, contradicting earlier claims of strong coupling. Simulations and data further show that low‑accretion Little Red Dots can evolve into the z≈0.7–2.5 red‑sequence ellipticals hosting relatively low‑mass BHs, eliminating the need for cosmological coupling. This links JWST LRD demographics to later ETG BH masses while removing BHs as a viable dark‑energy source.

LRD JWST AGN demographics high-z simulation

2025-06-21 · 2506.17641v1

Dark Bondi Accretion Aided by Baryons and the Origin of JWST Little Red Dots

Wei-Xiang Feng, Hai-Bo Yu, Yi-Ming Zhong

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Proposes an SIDM-driven seeding pathway for JWST little red dots in which gravothermal core collapse, sped up by central baryons, makes a tiny seed that grows first via baryonic Eddington accretion and then rapidly through dark Bondi inflow of SIDM. Demonstrates that black holes can reach ~10^7 Msun within ~500 Myr after the formation of ~10^9 Msun halos at z≈4–11, with most of the final mass supplied by dark matter rather than gas. Fluid simulations with and without a Plummer-fit baryonic potential show that baryons substantially shorten the collapse timescale and establish conditions for efficient dark-sector Bondi growth. The framework naturally explains the overmassive BH-to-stellar ratios in LRDs and links them to SIDM cross sections consistent with galaxy-scale structure data.

LRD BH seeds overmassive BH simulation high-z

2025-06-17 · 2506.14870v1

JADES and BlackTHUNDER: rest-frame Balmer-line absorption and the local environment in a Little Red Dot at z = 5

Francesco D'Eugenio, Ignas Juodžbalis, Xihan Ji, et al.

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Reports a broad-line Little Red Dot at z=5.077 (JADES-GS+033223.41-275404.5/159717) with NIRSpec MSA+IFU, revealing multi-component Hα including two broad Gaussians. A virial black hole mass of log(MBH/M⊙)=7.65 and a narrow [O III] λ5007-based dynamical mass of log(Mdyn/M⊙)=9.1 imply a BH overmassive relative to its host. The source sits in a 7-kpc pool of ionized gas with three neighbors (a satellite, a possible satellite/gas cloud, and a tentatively detected spatially detached outflow). A deep rest-frame Hα absorber (deeper than the continuum; v=-13 km s−1, σ=120 km s−1) appears in G395H but not G395M, with tentative EW variability over two rest-frame months (2.6σ), underscoring resolution- and time-dependent incidence of absorbers in LRDs.

LRD broad Balmer overmassive BH spectroscopy outflows variability

2025-06-13 · 2506.12141v1

A big red dot at cosmic noon

Federica Loiacono, Roberto Gilli, Marco Mignoli, et al.

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JWST reveals BiRD, a luminous little red dot at z=2.33 in the J1030 field, flagged as a bright outlier in the F200W−F356W vs F356W diagram. NIRCam/WFSS detects He I λ10830 and Paγ with both narrow and broad components (FWHM ≳ 2000 km s−1), plus a blueshifted He I absorption indicating dense outflowing gas with N(He I*, 2^3S) ≈ 0.5–1.2×10^14 cm−2 at Δv ≈ −830 km s−1; the source lacks X-ray and radio emission. The Paγ broad component implies MBH ≈ 10^8 M⊙ and Lbol ≈ 2.9×10^45 erg s−1, echoing GN-28074 and RUBIES-BLAGN-1 where similar He I absorption is seen. A first JWST-based census places the LRD space density at z<3 within a factor ∼2–3 of UV-selected quasars at comparable Lbol and MBH, arguing that LRDs contribute meaningfully to AGN demographics at cosmic noon and may trace rapid seed growth.

LRD broad-line AGN spectroscopy outflows demographics BH seeds

2025-06-05 · 2506.05459v1

RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines

Raphael E. Hviding, Anna de Graaff, Tim B. Miller, et al.

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RUBIES delivers uniform NIRSpec PRISM+G395M spectroscopy for ~1500 z>3.1 sources, identifying 80 broad-Balmer emitters, including 28 (35%) at z>6. A coherent subpopulation of 36 shows v-shaped UV–to–optical continua with dominant rest‑optical point sources; these are defined as spectroscopic LRDs, the largest such sample to date. The key result is that every v‑shaped point source exhibits broad Balmer lines, tying continuum shape, compact morphology, and AGN kinematics together. Photometric LRD searches recover only 50–62% of these to F444W<26.5, implying current color cuts miss many due to faint rest‑UV, comparatively bluer rest‑optical colors, or uncertain photo‑z.

LRD broad Balmer v-shaped SED spectroscopy demographics high-z

2025-06-04 · 2506.04350v1

JWST Insights into Narrow-line Little Red Dots

Zijian Zhang, Linhua Jiang, Weiyang Liu, et al.

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Using NIRSpec medium/high-resolution data and line-free photometry, the authors isolate five narrow-line LRDs at z≈5 (H-alpha FWHM ≈250 km/s; one ≈475 km/s) from 32 LRDs with H-alpha coverage, and show that about 20% of color-selected LRD candidates fake a V-shape continuum via strong lines. Relative to normal star-forming galaxies, these objects have higher H-alpha widths and luminosities but smaller equivalent widths. SED fits allow either dusty, compact, high-M* and high-SFR galaxies or low-mass AGN with MBH≈10^5–10^6 Msun, plausibly in an early, super-Eddington phase; the BHs are slightly overmassive vs MBH–M* yet consistent/undermassive vs MBH–sigma and MBH–Mdyn within large errors. Nearly half of high‑z broad-line AGN show V‑shape SEDs, underscoring that LRD-like photometry does not uniquely imply broad-line activity.

LRD spectroscopy v-shaped SED super-Eddington overmassive BH high-z

2025-06-04 · 2506.04004v1

Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions

María Carranza-Escudero, Christopher J. Conselice, Nathan Adams, et al.

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Builds a 124-object little red dot sample at z≈3–10 from CEERS, NEP‑TDF, JADES, and JEMS, then tests SED fits with and without AGN components using BIC. Despite lower χ² when adding AGN templates, BIC generally prefers non‑AGN SEDs, especially when MIRI photometry is included. KS tests of projected environments show LRDs occupy sparser neighborhoods than comparison galaxies, and abundance matching yields conservative halo-mass upper limits. Together these point to most LRDs being compact galaxies or forming star clusters rather than AGN‑dominated, while allowing for a mixed population.

LRD demographics high-z

2025-06-03 · 2506.03244v1

Cosmic Outliers: Low-Spin Halos Explain the Abundance, Compactness, and Redshift Evolution of the Little Red Dots

Fabio Pacucci, Abraham Loeb

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Proposes that Little Red Dots are the visible outcomes of galaxies forming in the extreme low-spin tail of the halo angular-momentum distribution, using Mo–Mao–White scaling to link halo spin to compact disk sizes. Assuming progenitors in the lowest ~1% of spins at z ~ 5 reproduces both the observed number densities and compact effective radii of ~80–300 pc, without requiring a choice between BH- or star-dominated power. The observed redshift trend arises from the competition between an increasing compact-halo fraction and cosmological surface-brightness dimming, yielding an “LRDs Era” at 4 < z < 8; at z < 4 they are bright but rare, while at z > 8 they are common but faint. Agreement with current counts, plus excess small-scale clustering and spectral signs of extreme core densities, supports the low-spin origin.

LRD simulation compact red high-z demographics

2025-05-28 · 2505.22600v1

Dust Budget Crisis in Little Red Dots

Kejian Chen, Zhengrong Li, Kohei Inayoshi, et al.

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Re-assessing LRD dust, the authors forward-model UV–IR SEDs across multiple extinction laws and dust geometries, then demand consistency with JWST/MIRI, Herschel, and ALMA fluxes and limits. They find A_V ≲ 1.0–1.5 mag under an SMC law for A2744-45924, RUBIES-BLAGN-1, and stacked LRD SEDs, with only slightly weaker bounds for gray UV extinction. These moderate extinctions alleviate the “dust budget crisis” for hostless/low-mass systems and imply ≈10% radiative efficiencies, easing Sołtan-argument tension. The work predicts testable far-IR reprocessed spectra, reframing early black-hole growth pathways for LRDs.

2025-05-28 · 2505.22567v1

A black hole in a near-pristine galaxy 700 million years after the Big Bang

Roberto Maiolino, Hannah Uebler, Francesco D'Eugenio, et al.

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JWST/NIRSpec-IFS dissects the triply imaged Little Red Dot Abell2744-QSO1 at z=7.04, isolating the narrow Hβ to map line ratios. [OIII]5007 is exceptionally weak—[OIII]/Hβn ≈ 0.6 within r<150 pc and <0.32 at 150–300 pc—implying Z ≈ 8×10^-3 Z⊙ centrally and Z<6×10^-3 Z⊙ in the extended gas, while broad Balmer lines/variability yield MBH ≈1.5×10^7 M⊙ in a host with Mdyn ≈10^7.1–10^8 M⊙. This places a massive black hole in an almost pristine, very low-mass galaxy only ~700 Myr post-Big Bang. The chemistry and mass budget strain heavy-seed or super‑Eddington growth paths, motivating alternatives such as primordial black-hole seeds that remain to be fully tested.

LRD high-z BH seeds overmassive BH spectroscopy broad Balmer

2025-05-26 · 2505.20439v1

The Properties of Little Red Dot Galaxies in the ASTRID Simulation

Patrick LaChance, Rupert A. C. Croft, Tiziana Di Matteo, et al.

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Using the ASTRID cosmological simulation, the authors generate mock NIRCam-like views at z=5–8 and identify 17 systems that meet little red dot color-plus-size cuts. These ASTRID LRDs are massive, compact, and dusty—log(M*/Msun)≥9.7, log(MBH/Msun)≥6.8, r_half,*=325–620 pc, with F444W attenuation >1.25—and are bright at F444W=23.5–25.5. Their recent quenching and a dust-obscured AGN produce a steep rest-optical red slope while UV light is star-dominated, pointing to an AGN-feedback-driven miniquenching phase. Lower-mass/fainter galaxies lack sufficient central dust, and many highest-Eddington BH hosts are not LRDs because high SFRs and low attenuation yield flatter spectra; the paucity of low-mass LRDs may partly reflect limited resolution.

LRD simulation obscured AGN compact red high-z

2025-05-26 · 2505.20393v1

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

Ming-Yang Zhuang, Junyao Li, Yue Shen, et al.

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Using NIRCam/WFSS F322W2+F444W in the central 100 arcmin² of NEXUS, the team secures a spectroscopic census of 23 BLAGNs at 3≲z≲6, 15 of which satisfy Little Red Dot criteria. The sample spans L(Hα)≈10^{42.2}–10^{43.7} erg s⁻¹, M_BH≈10^{6.3}–10^{8.4} M_⊙, and λ_Edd≈0.1–1 (median 0.4); about half of the LRDs show strong Balmer absorption indicating dense gas near the emission region. Most LRDs reveal extended (hundreds of parsec) rest-UV/optical host emission that significantly or dominantly contributes to the UV, explaining the characteristic UV upturn, and the LRD number density is ≈10⁻⁵ cMpc⁻³ with a mild decline toward lower z. Small-scale (≲1 cMpc) cross-correlations give a BLAGN bias of ~3.3 and halo masses of a few×10¹¹ h⁻¹ M_⊙, while LRD clustering appears overly strong for their space density, hinting at excess small-scale clustering; the single-epoch M_BH and λ_Edd carry large systematics.

LRD broad-line AGN spectroscopy broad Balmer demographics high-z

2025-05-24 · 2505.18873v1

An upper limit of 10$^6$ M$_\odot$ in dust from ALMA observations in 60 Little Red Dots

Caitlin M. Casey, Hollis B. Akins, Steven L. Finkelstein, et al.

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ALMA Band-6 (1.3 mm) continuum follow-up of 60 of the reddest and brightest COSMOS-Web little red dots—preselected with MIRI F770W detections—finds no individual detections and a non-detection in the stack. The data reach a mean σ_rms≈22 μJy, with a stacked flux of S_1.3mm=2.1±2.9 μJy, implying 3σ limits of Mdust<10^6 M⊙ and Ldust≲10^11 L⊙, about 10× deeper than previous submm stacks. These results disfavor large, cold dust reservoirs in typical LRDs. They are consistent with compact, modest dust columns (A_V~2–4) or extreme Balmer breaks from very dense gas (n>10^9 cm^-3) enshrouding a central black hole.

2025-05-19 · 2505.12719v1

Composite spectrum of Little Red Dot from a standard inner disk and an unstable outer disk

Chenxuan Zhang, Qingwen Wu, Xiao Fan, et al.

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Builds SEDs for 29 broad-line LRDs and finds uniformly V-shaped continua with a narrow break around ν_b ≃ 10^{14.96±0.06} Hz (λ ≈ 2600–3800 Å). Models the SEDs as a composite of an inner standard thin disk plus an outer gravitationally unstable disk (Q≈1) that self-regulates to T≈2000–4000 K, naturally producing the near-IR/optical bump without invoking extreme dust. MCMC fits anchored by MBH from broad lines reproduce individual SEDs, including UNCOVER 25119 and PRIMER 33823 (whose MIRI 4.9–27.9 μm points trace the bump). Allowing for dense gas to explain strong Balmer breaks suppresses intrinsic optical–UV by only ≲2–3×, implying most LRDs are sub-Eddington and intrinsically weak.

LRD v-shaped SED broad-line AGN spectroscopy high-z

2025-05-14 · 2505.09669v1

Chandra Rules Out Super-Eddington Accretion Models For Little Red Dots

Andrea Sacchi, Akos Bogdan

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Stacks Chandra data for 55 JADES/NGDEEP-selected little red dots in the 7 Ms CDF-S, reaching ~390 Ms effective exposure, yet finds no soft- or hard-band signal. The resulting flux limits translate to bolometric luminosities more than an order of magnitude below those inferred from JWST, directly ruling out current super-Eddington SED models tailored for LRDs. The non-detections are instead consistent only with extreme obscuration, requiring NH ≳ 10^25 cm^-2. The authors therefore argue the SMBHs in LRDs are likely less massive and/or less luminous than currently claimed.

LRD X-ray obscured AGN super-Eddington high-z

2025-05-14 · 2505.09542v1

A weak Ly$α$ halo for an extremely bright Little Red Dot: Indications of enshrouded SMBH growth

Alberto Torralba, Jorryt Matthee, Gabriele Pezzulli, et al.

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Deep VLT/MUSE mapping around the ultra-luminous LRD A2744-45924 (z=4.464, μ=1.8; L_Hα≈10^44 erg s^-1) reveals a modest, spatially offset Lyα halo with exponential scale length ≈5.7 pkpc and a narrow line (FWHM 270±15 km s^-1) whose flux is only 7% of Hα. Compact N IV] λ1486 coincides with the point-like Hα seen by JWST, while the far-UV continuum centroid shifts with the Lyα offset. The authors argue Hα traces the AGN whereas Lyα is powered by star formation; four neighboring Lyα halos (Δz<0.02, Δr<100 pkpc) show no luminosity excess indicative of AGN illumination. Altogether this points to a dense, near-unity covering-factor cocoon that shrouds the SMBH, suppressing UV/ionizing escape and signaling enshrouded early black-hole growth.

LRD obscured AGN spectroscopy broad Balmer high-z

2025-05-11 · 2505.06965v1

Black Hole Envelopes in Little Red Dots

Daisaburo Kido, Kunihito Ioka, Kenta Hotokezaka, et al.

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Proposes that little red dots host super-Eddington black holes wrapped in a massive, optically thick envelope that gravitationally confines otherwise destructive winds, effectively making outflows a no-go. The envelope radiates near the system Eddington limit with a photosphere at 5000–7000 K, naturally producing the red optical continuum and the hallmark V-shaped SED while explaining weak X-ray/radio and low short-term variability. A sustained ISM infall of ~1 M_sun/yr feeds the envelope, and a photospheric radius ~0.01 pc sets year-scale variability, linking LRD nuclear structure to Hayashi-limit physics. The envelope both regulates feedback and provides a reservoir enabling rapid early BH growth.

LRD stellar envelope v-shaped SED super-Eddington variability high-z

2025-05-09 · 2505.06359v1

JWST/NIRSpec Observations of High Ionization Emission Lines in Galaxies at High Redshift

Mengtao Tang, Daniel P. Stark, Adèle Plat, et al.

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Deep NIRSpec R=2700 spectroscopy of 53 new z>4 galaxies, plus a census of 851 archival spectra, is used to track high-ionization UV lines. The team reports narrow NV λ1240 in two systems—CEERS‑7902 (z=6.98; an LRD with broad Hβ) and CEERS‑1025 (z=8.72; narrow-line)—while CIV and He II are absent, yielding extreme NV/CIV and NV/He II. The inferred incidence of narrow high-ionization UV lines is 12.5(+23.7/−10.4)% in LRDs and 2.2(+1.7/−1.0)% in UV-selected galaxies at z>4, implying hard radiation fields in a small subset and that dense H I may not fully cover some LRD nuclei. The line ratios and non-detections argue for extending searches down to the NV doublet, though statistics remain limited by the number of deep rest-UV spectra.

LRD spectroscopy high-z broad Balmer demographics

2025-05-08 · 2505.05556v1

Super-Eddington accretion in high-redshift quasar hosts: Black-hole driven outflows, galaxy quenching, and the nature of little red dots

Giada Quadri, Alessandro Trinca, Alessandro Lupi, et al.

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Zoom-in cosmological simulations of a quasar host including super-Eddington accretion track how MBH feedback shapes gas, star formation, and emergent spectra. Outflows usually vent perpendicular to the disc and only moderately suppress the SFR, but after rapid super-Eddington growth the galaxy spends ≈10% of its lifetime in a distinct quenched state. This phase culminates in a powerful jet+disc-wind event that couples to the disc and excavates a central cavity. Across its history the system’s spectra can look like little red dots or quenched galaxies, implying both are transient stages in early quasar hosts.

simulation super-Eddington outflows LRD high-z QSO

2025-05-07 · 2505.04609v1

CAPERS-LRD-z9: A Gas Enshrouded Little Red Dot Hosting a Broad-line AGN at z=9.288

Anthony J. Taylor, Vasily Kokorev, Dale D. Kocevski, et al.

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CAPERS-LRD-z9 is a PRIMER-selected little red dot spectroscopically confirmed with NIRSpec/PRISM as a z=9.288 broad-line AGN via a ~3500 km s−1 Hβ plus narrow [O III] λλ4959,5007. The broad Hβ implies a canonical black-hole mass log(MBH/M⊙)=7.58±0.15 (allowing 6.65–8.50 with systematics). A pronounced Balmer break requires a dense (~10^10 cm−3) neutral-gas cocoon around the nucleus; SED modeling (CLOUDY+bagpipes) limits the host to M*<10^9 M⊙, hinting at MBH/M* possibly >5% and a UV continuum that may be AGN-dominated. Together, these properties push early BH growth scenarios toward massive seeds or super‑Eddington episodes within ≲500 Myr of cosmic time.

LRD broad-line AGN high-z broad Balmer spectroscopy BH seeds

2025-05-06 · 2505.03183v1

The Physical Nature of the Off-centered Extended Emission Associated with the Little Red Dots

Chang-Hao Chen, Luis C. Ho, Ruancun Li, et al.

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This Letter decomposes NIRCam imaging in 8 broad and 9 medium bands to isolate off-centered emission around four LRDs in Abell 2744 (UNCOVER + MegaScience). Three blobs are confirmed to be physically associated with their LRDs, with two showing medium-band excess consistent with very strong [O III] λλ4959,5007. While all three SEDs can be fit as ~10^8 Msun star-forming systems, the two [O III]-extreme cases are best explained as pure nebular emission from low-density, low-metallicity gas photoionized by the nearby LRD. Adopting LRD halo masses, the implied baryonic halo accretion rates are ~2–9 Msun/yr, suggesting growth to ~10^9 Msun by z≈4 if sustained at 10% star-formation efficiency.

LRD nebular continuum

2025-05-05 · 2505.02895v1

Abundant Population of Broad H$α$ Emitters in the GOODS-N Field Revealed by CONGRESS, FRESCO, and JADES

Junyu Zhang, Eiichi Egami, Fengwu Sun, et al.

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Using JWST/NIRCam WFSS from FRESCO and CONGRESS plus JADES imaging, the authors conduct a GOODS‑N search for broad Hα at z≈3.7–6.5 and confirm 19 emitters at z≈4–5.5, including nine new ones. Their broad Hα LF aligns with other JWST BLAGN results, and virial BH masses with bolometric corrections imply ≈0.1 Eddington accretion and elevated MBH/M* relative to local relations. Color comparisons show LRD cuts miss 42% of these spectroscopic AGN—many lack the steep rest‑optical red slope—and average SEDs indicate some LRD red slopes are line‑boosted. Notably, 68% of color‑selected LRDs with Hα detections lack broad lines in the grism data, potentially due to sensitivity limits, underscoring the LRD population’s mixed nature.

broad-line AGN broad Balmer spectroscopy demographics LRD high-z

2025-04-10 · 2504.08032v1

Counting Little Red Dots at $z<4$ with Ground-based Surveys and Spectroscopic Follow-up

Yilun Ma, Jenny E. Greene, David J. Setton, et al.

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Using ~3.1 deg^2 of ultra-deep HSC plus (near-)IR imaging, the authors assemble a ground-based sample of Little Red Dots at 2≲z≲4 and measure their abundance for M5500<-22.5. They find a sharp decline in number density from ~10^-4.5 cMpc^-3 at z>4 to ~10^-5.3 at 2.7<z<3.7 and ~10^-5.7 at 1.7<z<2.7, extending LRD demographics below z~4. A Magellan/FIRE spectrum of DEEP23-z2LRD1 (z_spec=2.26) shows broad Hα (FWHM≈2400 km s^-1) plus nearly symmetric narrow Hα absorption and extremely narrow [OIII] (FWHM≈140 km s^-1), consistent with an accreting BH in a low-mass host. Because ground-based resolution limits can admit contaminants, the paper stresses that spectroscopy is required to firm up the z<4 LRD number densities.

LRD demographics spectroscopy broad Balmer low-z

2025-04-09 · 2504.07196v1

Joint Survey Processing. III. Compact Oddballs in the COSMOS Field -- Little Red Dots and Transients

Yu-Heng Lin, Andreas L. Faisst, Ranga-Ram Chary, et al.

HST/ACS G800L grism follow-up of seven compact, 8000 Å–dropout COSMOS point sources tests the faint z≈6 AGN candidate pool. Only one object (772319) is detected in multiple bands with a V-shaped, LRD-like SED and is ~3 mag brighter than typical JWST LRDs; no Lyα or other common lines appear in the grism. From the non-detections they place an upper limit on the AGN UV luminosity function of Φ=1.1×10^-7 Mpc^-3 mag^-1 at M_UV=−21. The remaining sources show F814W vs Subaru i+z flux mismatches not attributable to emission lines, implying long-lived transients with observed-frame decay timescales ≤6 years and highlighting transient contamination of faint-AGN searches.

LRD v-shaped SED high-z spectroscopy demographics

2025-04-02 · 2504.01852v1

Deciphering the Nature of Virgil: An Obscured AGN Lurking Within an Apparently Normal Lyman-α Emitter During Cosmic Reionization

Pierluigi Rinaldi, Pablo G. Pérez-González, George H. Rieke, et al.

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JWST/MIRI imaging plus deep NIRSpec/PRISM place the LAE “Virgil” at z=6.6379 and reveal Little Red Dot–like photometry with an extreme color F444W−F1500W=2.84±0.04, and a strongly rising mid-IR SED. SED fits across multiple codes favor an obscured AGN whose IR slope and UV excess resemble blue-excess HotDOGs. The host shows subsolar metallicity, low–moderate dust, and high ionization/electron temperature; UV and Hα SFRs suggest Virgil is entering or fading a burst. High‑z line‑ratio diagnostics (e.g., O32–R23, Ne3O2) nominally flag AGN, though this is ambiguous after accounting for redshift evolution; a tentative broad Hα improves residuals only marginally, while the new 15 μm data strengthen the AGN case and highlight MIRI’s leverage on early black‑hole growth.

LRD obscured AGN JWST AGN high-z spectroscopy reionization

2025-03-31 · 2504.00172v1

Evidence for evolutionary pathway-dependent black hole scaling relations

Jonathan H. Cohn, Emmanuel Durodola, Quinn O. Casey, et al.

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This letter benchmarks secure dynamical black hole masses in a z~2 lensed quiescent galaxy and six local red‑nugget relics against recent 4<z<11 AGN, quasar, and Little Red Dot samples on the M_BH-M_star and M_BH-sigma_* planes. The relics and the z~2 quiescent system land on both the local bulge M_BH-M_star relation and the 4<z<7 Pacucci et al. relation, while luminous QSOs and broad-line AGN follow Pacucci et al. more closely and LRDs scatter across all three; on M_BH-sigma_* most sources sit above the local median except the lensed system. The authors argue the bulge relation was already in place at high z and that differing evolutionary pathways—compact-core assembly by z~2 followed by dry-merger stellar-mass growth versus ongoing BH and star formation in AGN—govern positions on scaling planes. Given large systematics in single‑epoch high‑z masses, they emphasize dynamical detections in relics and strongly lensed galaxies as a complementary, less biased probe of early scaling relations.

LRD overmassive BH demographics high-z low-z

2025-03-31 · 2503.23710v1

Formation of the Little Red Dots from the Core-collapse of Self-interacting Dark Matter Halos

Fangzhou Jiang, Zixiang Jiang, Haonan Zheng, et al.

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Using Monte Carlo merger trees, the authors model black hole seeding via gravothermal core-collapse in self-interacting dark matter halos and their subsequent growth at early times. Collapse occurs in rare, high-concentration halos at a characteristic mass scale set by the velocity-dependent cross section, naturally producing seeds early enough to explain compact, galaxy-poor little red dots. With simple growth assumptions and a 100% duty cycle, the model reproduces the observed LRD black hole mass function for σ0m ~ 30 cm^2 g^-1 and ω ~ 80 km s^-1, consistent with independent local constraints. If σ0m or ω are higher, the resulting overproduction at one end of the mass function can be mitigated by a reduced duty cycle or lower Eddington ratios, suggesting high‑z BH demographics as a probe of SIDM physics.

LRD BH seeds simulation demographics high-z

2025-03-20 · 2503.16600v1

A remarkable Ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a Little Red Dot at $z=3.5$

Anna de Graaff, Hans-Walter Rix, Rohan P. Naidu, et al.

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JWST/NIRSpec+NIRCam+MIRI data on The Cliff, a luminous Little Red Dot at z=3.55, reveal an extreme Balmer break—about twice stronger than any previously seen at high-z—alongside broad Hα (FWHM∼1500 km s⁻¹) and He I emission but no significant metal lines. Stellar-population solutions (even with steep dust or IMF tweaks) fail, and their formal M*∼10^10.5 M⊙ with re∼40 pc would imply implausibly high stellar-collision rates. The spectra and continuum are instead best matched by a “black hole star” configuration: a powerful central ionizing source embedded in dense, absorbing gas that imprints the Balmer edge and Hα absorption while favoring an intrinsically red continuum over heavy dust. This makes The Cliff compelling evidence that at least some LRDs are not ultra-dense galaxies but compact, accretion-powered nuclei shrouded by dense gas.

LRD broad Balmer stellar envelope super-Eddington spectroscopy high-z

2025-03-20 · 2503.16596v1

A "Black Hole Star" Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots

Rohan P. Naidu, Jorryt Matthee, Harley Katz, et al.

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JWST/NIRSpec spectroscopy of the point-like source MoM-BH*-1, observed ~660 Myr after the Big Bang, reveals an enormous Balmer break, broad multi-peaked Hβ, and deep Balmer-line absorption. The authors model it as a “black hole star”: a supermassive black hole enshrouded by extremely dense, turbulent, dust-free gas whose atmosphere imprints the break and absorption while dominating the observed light; narrow [OIII] and residual UV are attributed to a faint host. The data are well matched by a simple Cloudy setup that reproduces the break strength, Balmer EWs, UV faintness, and MIRI continuum, with line ratios consistent with high densities that can collisionally suppress [OIII] and a hint of variability reinforcing the SMBH interpretation. They further argue that Little Red Dots can be explained as BH*s embedded in comparably bright hosts, implying current LRD black hole masses—derived with steep dust corrections and standard scaling relations—may be overestimated by orders of magnitude.

LRD BH seeds super-Eddington stellar envelope broad Balmer high-z

2025-03-20 · 2503.16595v1

Little red dots as young supermassive black holes in dense ionized cocoons

V. Rusakov, D. Watson, G. P. Nikopoulos, et al.

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Using the highest-S/N JWST/NIRSpec spectra of LRD-like broad-line sources, the authors show that Balmer-line wings are exponential and symmetric, as expected from electron scattering in a compact, Compton-thick ionized cocoon. Convolving a narrow Doppler core with this scattering kernel yields intrinsic widths of only a few hundred km/s, implying black holes of ~10^5–10^7 M⊙ accreting near the Eddington limit within light‑day–scale gas with mild outflows. Accounting for scattering lowers previous mass estimates by ~2 dex and naturally explains LRD traits, including very weak X-ray/radio via nebular reprocessing. This reframes LRDs as young, rapidly growing SMBHs rather than overmassive quasars for their hosts.

LRD broad Balmer nebular continuum super-Eddington high-z

2025-03-19 · 2503.15323v1

Euclid Quick Data Release (Q1). Extending the quest for little red dots to z<4

Euclid Collaboration, L. Bisigello, G. Rodighiero, et al.

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Using 63 deg² from Euclid’s Quick Data Release (Q1) plus IRAC and ground-based griz, the team fits two power laws to photometry to isolate little red dots with blue UV and red optical slopes while removing extended sources, strong line emitters, and artifacts. They assemble 3341 LRD candidates at z=0.33–3.6 (29 with IRAC), and derive a rest‑frame UV luminosity function that rises from high z down to z≈1.5–2.5 before declining toward lower redshift. Comparing to quasar UV LFs shows LRDs are not the dominant AGN population at z<4 for M_UV<-21. A noted caveat is that evolution inferred from the IRAC‑detected subsample is limited by small numbers and IRAC’s resolution, motivating follow‑up.

LRD v-shaped SED demographics low-z

2025-03-14 · 2503.11752v1

BlackTHUNDER strikes twice: rest-frame Balmer-line absorption and high Eddington accretion rate in a Little Red Dot at $z=7.04$

Francesco D'Eugenio, Roberto Maiolino, Michele Perna, et al.

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BlackTHUNDER re-analyzes JWST/NIRSpec-IFS G395H data for the Little Red Dot Abell2744-QSO1 at z=7.04, focusing on the Hα region. The Hα profile is distinctly non-Gaussian, requiring at least two broad Gaussians plus a narrow component, and shows strong rest-frame Balmer-line absorption (EW ≈22 Å) centered at the systemic velocity of the broad line; the absorber’s dispersion (σ_abs ≈110 km s⁻¹) matches that inferred from the Balmer break, arguing for a long‑lived, non-flowing structure. An Hα-based virial mass of log(MBH/M⊙) ≈7.2 and a deconvolved narrow-line width σ_n ≈22 km s⁻¹ yield MBH/Mdyn = 0.15–1.2, confirming an overmassive black hole with limited room for a host galaxy. The revised mass implies high accretion, λ_Edd ≈0.7–1.6 (potentially super‑Eddington at the low‑mass end), tying Balmer-break strength directly to Balmer-line absorption in LRDs.

LRD broad Balmer stellar envelope overmassive BH super-Eddington spectroscopy

2025-03-13 · 2503.10958v1

Dot to dot: high-$z$ little red dots in $M_{\rm bh}$-$M_{\rm \star}$ diagrams with galaxy-morphology-specific scaling relations

Alister W. Graham, Igor V. Chilingarian, Dieu D. Nguyen, et al.

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Places high‑z little red dots onto morphology‑aware Mbh–M★ diagrams alongside compact stellar systems and local galaxy sequences. With 2023–2024 masses, LRDs are not NSCs (NSCs have higher Mbh/M★); the least‑massive LRDs overlap UCD‑like Mbh and M★, and the full LRD set spans from UCDs to primaeval S0s, while spirals and merger‑built ETGs sit at higher M★. Low‑z AGN align with the quasi‑quadratic/steeper relations defined by local disc galaxies with direct black‑hole masses, emphasizing morphology in coevolution. As 2025 mass updates arrive, placements may shift, potentially bringing LRDs closer to NSCs/UCDs/green‑peas.

LRD overmassive BH demographics high-z

2025-03-07 · 2503.05537v1

Little Red Dots as the Very First Activity of Black Hole Growth

Kohei Inayoshi

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Using 341 Little Red Dots (39 with spectroscopic redshifts) compiled from JWST surveys, this paper models their occurrence across cosmic time. The counts peak at z ~ 6–8 and fall steeply by z < 4, well described by a log‑normal distribution interpreted as the first one or two accretion episodes of newborn seed black holes. Dense circumnuclear gas naturally explains broad Balmer-line absorption, X‑ray weakness, and brief super‑Eddington bursts that yield overmassive BHs relative to local relations. Summing recurrent episodes reproduces the global AGN abundance evolution ∝ (1+z)^(−5/2) and provides an analytic form for the LRD redshift dependence for future tests.

LRD BH seeds super-Eddington overmassive BH demographics high-z