The Extreme Quasar Main Sequence of Super-Eddington DESI-DR1 NLSy1 Galaxies

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Results. The DESI-DR1 NLSy1 population shows a striking shift toward the extreme end of the EV1 parameter space, possessing stronger Fe II emission (median log ⁡ R 4570 = − 0.03 \log R_{4570}=-0.03 ) compared to the SDSS sample ( − 0.31 -0.31 ). Furthermore, the DESI sources systematically harbor less massive black holes (median log ⁡ M BH / M ⊙ ≈ 6.73 \log M_{\text{BH}}/M_{\odot}\approx 6.73 in both calibrations) than the SDSS objects ( 6.77 − 6.91 6.77-6.91 ). Given their comparable continuum luminosities, a consistently larger fraction of the DESI sample (43.8%–47.7%) is pushed across the Eddington limit ( log ⁡ R E ​ d ​ d > 0 \log R_{Edd}>0 ) compared to the SDSS sample (20.6%–37.4%).

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In this work, we have utilized the unprecedented sensitivity of the DESI-DR1 survey to identify and characterize a new, large sample of 18,749 Narrow-Line Seyfert 1 galaxies ( DESI Collaboration, 2025 ) . By projecting this sample onto the EV1 parameter space and comparing it against the SDSS-DR17 NLSy1 population ( Paliya et al., 2024 ) , we reach the following conclusions: (1) The DESI-DR1 survey has uncovered a distinct, extreme tail of the quasar main sequence. The DESI-NLSy1 galaxies show stronger Fe II emission (median log ⁡ R 4570 = − 0.03 ± 0.52 \log R_{4570}=-0.03\pm 0.52 ) compared to previously known SDSS-NLSy1s (median log ⁡ R 4570 = − 0.31 ± 0.29 \log R_{4570}=-0.31\pm 0.29 ). (2) This EV1 shift is likely to be driven by a population of lower-mass supermassive black holes. The median single-epoch virial mass for the DESI sample is log ⁡ ( M BH / M ⊙ ) = 6.73 ± 0.42 \log(M_{\text{BH}}/M_{\odot})=6.73\pm 0.42 , significantly lower than the SDSS sample ( log ⁡ ( M BH / M ⊙ ) = 6.91 ± 0.37 \log(M_{\text{BH}}/M_{\odot})=6.91\pm 0.37 ). (3) Coupling their lower black hole masses with their continuum luminosities reveals that a substantial fraction of the DESI-NLSy1 population (43.8%, compared to 20.6% for SDSS) is accreting at or above the Eddington limit. Although applying the Eddington-dependent Woo et al. (2026) calibration reduces the gap between the two samples (47.7% vs. 37.4%), the overall trend remains consistent, robustly confirming their extreme accretion states.

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Because the physical interpretation of the DESI-NLSy1 sample relies heavily on their extreme Eddington ratios, integrating two independent mass calibrations confirms that our results are not likely to be methodological artifacts. Comparing the individual mass estimates from the two methods reveals that while the SDSS population experiences a downward shift in mass when transitioning from the Du & Wang (2019) to the Woo et al. (2026) calibration (median dropping from 6.91 6.91 to 6.77 6.77 ), the DESI-NLSy1 sample remains stable (median log ⁡ M BH / M ⊙ ≈ 6.73 \log M_{\text{BH}}/M_{\odot}\approx 6.73 in both). This is likely because these sources serve as the “ground truth” for extreme, super-Eddington accretors, they already naturally occupy the high-Eddington regime that the fundamental plane is explicitly designed to describe. Conversely, the SDSS sample may be more heterogeneous, containing transition-regime sources that required this calibration correction. Thus, the prevalence of super-Eddington accretion in the DESI population is a robust result, rather than a calibration artifact.

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Ultimately, this extreme EV1 sample provides a rich statistical dataset of local super-Eddington accretors. Future multi-wavelength investigations, including reverberation mapping to calibrate their virial masses and high-resolution host galaxy imaging, will be pivotal in unravelling the physics governing the extreme faint end of the AGN population.

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Conclusions. The unprecedented sensitivity of DESI has unveiled a large population of low-mass, super-Eddington accreting AGN that were largely missing from previous surveys. These extreme EV1 objects struggle to process luminous accretion flows, naturally producing the observed intense Fe II emission. This unique sample provides a rich statistical dataset of local super-Eddington accretors, serving as laboratories for understanding early-Universe black hole growth.

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Figure 1: (Left) The EV1 diagram displaying Fe II strength ( R 4570 R_{4570} ) versus broad H β \beta FWHM. The DESI-DR1 parent AGN sample (BLSy1 + NLSy1) is shown in the background (green) to illustrate how NLSy1 galaxies populate the extreme tail of the main sequence. The deep sensitivity of DESI-DR1 (blue) reveals a profound shift toward extreme Fe II emission compared to SDSS-DR17 (red). Smoothed contours trace 40%, 65%, and 85% of the maximum density for the NLSy1 samples. (Middle) Accretion rate versus black hole mass using the Du & Wang (2019) calibration. A much larger fraction (43.8% vs. 20.6% for SDSS) of the DESI sample crosses the Eddington limit (black dashed line). (Right) The R Edd R_{\text{Edd}} – M BH M_{\text{BH}} plane projected using the Woo et al. (2026) fundamental plane masses, robustly confirming the DESI population’s super-Eddington nature, with an even larger fraction (47.7% vs. 37.4% for SDSS) crossing the Eddington limit.

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Despite possessing lower black hole masses, the DESI sources maintain comparable continuum luminosities to the SDSS sample ( Paliya et al., 2026 , see the parameter distributions in) . Consequently, a significantly larger fraction of the DESI-DR1 population is pushed upward in the R Edd R_{\text{Edd}} – M BH M_{\text{BH}} plane, directly crossing the Eddington limit ( log ⁡ R Edd > 0 \log R_{\text{Edd}}>0 ). When utilizing the Du & Wang (2019) calibration, the median Eddington ratio is log ⁡ R Edd = − 0.07 ± 0.46 \log R_{\text{Edd}}=-0.07\pm 0.46 for the DESI sample, compared to − 0.29 ± 0.36 -0.29\pm 0.36 for SDSS, with 43.8% of the DESI sample crossing the super-Eddington limit versus 20.6% for SDSS. Applying the Woo et al. (2026) fundamental plane calibration reduces the median mass estimates to log ⁡ ( M BH / M ⊙ ) = 6.73 \log(M_{\text{BH}}/M_{\odot})=6.73 for DESI and 6.77 6.77 for SDSS. This correspondingly shifts the median Eddington ratios to log ⁡ R Edd = − 0.02 ± 0.37 \log R_{\text{Edd}}=-0.02\pm 0.37 for DESI and − 0.11 ± 0.34 -0.11\pm 0.34 for SDSS. Under this relation (Figure 1 ), 47.7% of the DESI sample and 37.4% of the SDSS sample cross into the super-Eddington regime. While the difference between the two populations is reduced with this new calibration, the trend remains highly consistent. This robustly confirms that the extreme EV1 signatures are a direct observational consequence of their super-Eddington accretion states. These low-mass systems are struggling to process highly luminous accretion flows, providing a crucial local observational analog to the rapidly growing, overly massive high-redshift black hole seeds recently discovered by JWST ( Maiolino et al., 2024 ; Bogdán et al., 2024 , e.g.,) .

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While the evidence points toward a distinct population of super-Eddington accretors, it is crucial to acknowledge the uncertainties inherent to single-epoch virial black hole mass estimators. In highly accreting AGN, strong radiation pressure can accelerate BLR clouds, potentially leading to an underestimation of M BH M_{\text{BH}} and an overestimation of R Edd R_{\text{Edd}} . Although the primary catalogs implemented the Fe II-dependent R BLR R_{\text{BLR}} scaling relation ( Du & Wang, 2019 ) to mitigate these radiation pressure effects, the intrinsic scatter in these relations remains a dominant source of uncertainty, capable of introducing systematics as large as 0.4 0.4 dex ( Shen, 2013 ) .

abstract · abstract

The quasar main sequence, or Eigenvector 1 (EV1), describes the optical diversity of active galactic nuclei (AGN), with Narrow-Line Seyfert 1 (NLSy1) galaxies anchoring the high-accretion end. Recent discoveries of overly massive black holes in the early Universe highlight the need to study local, low-mass super-Eddington accretors as analogs of rapid black hole growth. We map a population of 18,749 NLSy1 galaxies identified in the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) onto the EV1 plane to determine whether they represent a distinct population of super-accretors. We compare the spectral properties of the DESI DR1 NLSy1 sample with the SDSS DR17 NLSy1 catalog. We extract key parameters, including the broad H-beta full width at half maximum (FWHM) and Fe II strength (R4570). To evaluate their accretion states, we derive single-epoch virial black hole masses using an Fe II strength-dependent scaling relation and an Eddington rate-dependent fundamental plane. The DESI DR1 NLSy1 population shows a shift toward the extreme end of the EV1 parameter space, with stronger Fe II emission (median log R4570 = -0.03) than the SDSS sample (-0.31). Furthermore, the DESI sources host less massive black holes (median log black hole mass ~6.73) than the SDSS objects (6.77-6.91). Given comparable continuum luminosities, a larger fraction of the DESI sample (43.8%-47.7%) exceeds the Eddington limit (log Eddington ratio > 0) than the SDSS sample (20.6%-37.4%). The sensitivity of DESI has unveiled a large population of low-mass, super-Eddington accreting AGN largely missing from previous surveys. These extreme EV1 objects naturally produce the observed intense Fe II emission. This unique sample provides a statistical dataset of local super-Eddington accretors for understanding early-Universe black hole growth.

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Context. The quasar main sequence, or Eigenvector 1 (EV1), describes the optical diversity of active galactic nuclei (AGN), with Narrow-Line Seyfert 1 (NLSy1) galaxies anchoring the high-accretion end. Recent discoveries of overly massive black holes in the early Universe highlight the need to study local, low-mass super-Eddington accretors as analogs for rapid black hole seed growth.

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Early observations of the host galaxy of nearby NLS1s revealed a very high fraction (up to 100%) of barred spirals ( Krongold et al., 2001 ; Crenshaw et al., 2003 ; Ohta et al., 2007 ) . The Hubble Space Telescope confirmed this result, showing that the vast majority of NLS1s are hosted in spirals with pseudobulges ( Mathur et al., 2012 ) . This supports the hypothesis that the black hole in NLS1s is fed by means of secular evolution, with the bar playing an essential role in transporting the gas from the outer regions of the galaxy to its nucleus ( Orban de Xivry et al., 2011 ) . This result is in agreement with studies on the large-scale environment of NLS1s, which, unlike other AGN, tend to be found either in voids or, more generally, in low-density environments ( Järvelä et al., 2017b ) . Additionally, the host galaxy of NLS1s is characterized by strong circumnuclear star formation, located in the bar or rings. These star-forming regions have been identified using polycyclic aromatic hydrocarbons as tracers ( Sani et al., 2010 ) , by their strong radio emission ( Caccianiga et al., 2015 ) or, more recently, by subtracting the nuclear point-spread function from integral-field observations ( Winkel et al., 2022 ) .

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could be misclassified as FSRQs or just grouped with the large category of unidentified Fermi objects ( Foschini et al., 2021 ; Foschini et al., 2022 ) . The existence of gamma-ray emitting NLS1s, in conclusion, proves that the blazar sequence is valid only if the sources have comparable black hole mass, but it needs to be updated if different mass ranges are included.

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The main Balmer lines, H α \alpha and H β \beta , both show narrow and broad components, indicating an unobscured view of the central engine. The broad components resulted to have a FWHM of 3675 km s -1 while the narrow components of 741 km s -1 (Tab. 2 ). The integrated fluxes for the single components are reported in Tab. 2 . Despite the H α \alpha -[N II] complex not being completely resolved, due to poor spectral resolution, fantasy could decompose the H α \alpha contribution from the [N II] doublet.

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Finally, the exceptionality of this source lies in its CL transition happening at high Eddington ratios, compared to the typical CL behaviour outlined in the Sect. 1 . However, recent results suggest that the threshold for such events can reach as low as 1 % \% of the Eddington ratio ( Jana et al. 2025 , , and references therein) .

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One of the most intriguing results from early observations with the James Webb Space Telescope (JWST) is the identification of an abundance of red and compact objects [ 76 , 11 , e.g.,] . These objects exhibit a unique “V-shape” spectral energy distribution (SED) that is red in the rest-frame optical and blue in the rest-frame ultraviolet (UV). They are called “Little Red Dots” (LRDs) for their compact morphology [ 6 , 39 , 44 , typical R eff ∼ 100 R_{\rm eff}\sim 100 pc; e.g.,] and red colors in the observed-frame ∼ 2 \sim 2 – 5 ​ μ ​ m 5~\mu m range [ 87 , e.g.,] . LRDs are ubiquitous at redshifts from z ∼ 4 z\sim 4 up to z ∼ 9 z\sim 9 [ 11 , 78 , 70 , 72 , e.g.,] , while at lower redshift their number density decline rapidly [ 70 , 83 , e.g.,] . Spectroscopy of more than one hundred photometrically identified LRDs reveals that ≳ 70 % \gtrsim 70\% of them exhibit broad Balmer lines [ 47 , 41 , 67 , 70 , 87 , 122 , e.g.,] .

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Based on the above procedure, we identify five narrow-line LRDs with no broad H α \alpha line component from the 32 sources. We also attempt to fit the H α \alpha lines of these five sources using two narrow Gaussian components (FWHM < < 1000 km ​ s − 1 \rm km~s^{-1} ). The resultant BIC value still favors the single narrow component model in each case. The fraction of narrow-line LRDs in our sample is ∼ 16 % \sim 16\% . This fraction may be biased by the complex selection process of the NIRSpec observations. On the other hand, we argue that the photometric selection is not sensitive to the line width, and thus the narrow-line LRD fraction is unlikely affected significantly.

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This spectral fitting procedure identifies 16 BLAGNs with SNR ( H α , b ) > 5 \rm SNR(\rm H\alpha_{,b})>5 . We then visually inspected their spectral and SED fitting results, along with images, to select the final BLAGN sample for studying the ℳ BH − ℳ ⋆ \textit{$\mathcal{M}_{\rm BH}$}-\textit{$\mathcal{M}_{\star}$} relation. The total flux used to calibrate the prism spectrum of 13025-JADES-GS was contaminated by nearby companions not successfully deblended by ASTRODEEP. We recalibrated the spectrum using PSF-matched photometry within a 0 . 5 ′′ 0.\textit{${}^{\prime\prime}$}5 -diameter aperture, which captures most of the emission from the BLAGN, and repeated the SED fitting. The updated stellar mass is ∼ 0.3 \sim 0.3 dex lower but remains consistent with a massive galaxy ( log ​ ℳ ⋆ / M ⊙ ∼ 10.34 \textit{${\rm log}\,\textit{$\mathcal{M}_{\star}$}$}/\textit{$M_{\odot}$}\sim 10.34 ). Additionally, we excluded two objects due to uncertain stellar mass estimates. Specifically, 106980-PRIMER-UDS exhibits a peculiar SED shape that cannot be fitted by our SED models, resulting in highly uncertain stellar mass estimates. 55620-PRIMER-UDS shows a characteristic V-shaped SED of little red dots Greene et al. (2024) . The origin of this shape remains debated, with different interpretations (e.g., scattered AGN light or a combination of a blue galaxy and a reddened AGN) leading to orders of magnitude differences in the derived stellar mass Wang et al. (2024) . Consequently, our final sample contains 14 BLAGNs hosted in “normal” massive galaxies, providing a lower limit of ∼ 27 % \sim 27\% (14/52) for the fraction of BLAGNs in our massive galaxy sample.

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Our results thus suggest that additional quenching mechanisms, not relying on overmassive BHs, are required to enable more efficient star formation quenching in simulations in order to reconcile with recent JWST observations of high-redshift massive quiescent galaxies Weller et al. (2024) ; de Graaff et al. (2024) . This could involve more effective supernova feedback and starburst-driven outflows than those currently implemented in cosmological simulations Deng et al. (2024) , or more efficient AGN feedback in the low BH mass regime. After quenching, stellar winds from old, evolved stars could become a major source of BH fueling. This effective growth channel, along with merging with other galaxies hosting overmassive BHs, may gradually establish the ℳ BH − ℳ ⋆ \textit{$\mathcal{M}_{\rm BH}$}-\textit{$\mathcal{M}_{\star}$} relation for local ellipticals Jahnke and Macciò (2011) ; Kormendy and Ho (2013) ; Aird et al. (2022) , and could explain the prevalence of AGN activity in quiescent galaxies Aird et al. (2022) ; Baker et al. (2024) . Ultimately, radio-mode feedback could be triggered in these fully grown massive BHs and sustain long-term quiescence of the host. Future spatially resolved studies of the stellar population, kinematics, outflows, radio activity, residual star formation and gas reservoir in our sample will provide critical insights into their formation history and inform upcoming high-resolution cosmological simulations.

abstract · abstract

JWST has revealed an abundance of supermassive black holes (BHs) in the early Universe, and yet the lowest mass seed black holes that gave rise to these populations remain elusive. Here we present a systematic search for broad-line Active Galactic Nuclei (AGNs) in some of the faintest high-$z$ galaxies surveyed yet by combining ultra-deep JWST/NIRSpec G395M spectroscopy with the strong lensing aid in Abell S1063. By employing the profile of the [OIII]$λ5007$ emission lines as a template for narrow-line components and carefully cross-validating with mock observations, we identify a sample of ten broad-line AGNs at $4.5<z<7.0$ (eight secure, two tentative). The inferred BH masses from the broad H$α$ line explore the intermediate BH mass regime down to $\sim 10^{5.5}\,M_\odot$. The stellar mass ($M_*$) is estimated with a galaxy+AGN composite model, and we find the BH to stellar mass ratio spans down to $M_{\rm BH}/M_*\lesssim 0.1\%$, unveiling populations on the empirical $M_{\rm BH}-M*$ relation observed in the local universe. We also derive the black hole mass function and investigate its low-mass end at this epoch. While we confirm the agreement of our results with previous studies at $M_{\rm BH}\gtrsim10^{6.5}M_{\odot}$, we find the mass range of $\sim 10^{5.5}\,M_\odot$ features an enhanced abundance with respect to the extrapolated best-fit Schechter function. Comparison with theoretical models suggests that a possible origin for this enhanced abundance is the direct-collapse BH formation, supporting the scenario that the direct collapse of massive gas clouds is a significant pathway for the earliest supermassive BHs.

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For sources with available multi-epoch spectroscopy, we performed a variability analysis for our sample. We found that 11 out of 13 sources ( 85 − 15 + 5 % 85^{+5}_{-15}\% ) exhibit variability either in flux (10/13, 77 − 15 + 8 % 77^{+8}_{-15}\% ) or N H N_{\rm H} (4/12, 33 − 10 + 15 % 33^{+15}_{-10}\% ). These results are in excellent agreement with recent findings on lower-luminosity ( log ⁡ L X / erg ​ s − 1 ∼ 43 \log L_{\rm X}/\mathrm{erg\,s^{-1}}\sim 43 ), Compton-thin AGNs.

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For 20/21 sources with adequate optical spectroscopy, we measured the [ Ne v ] λ ​ 3426 \lambda 3426 emission line and found a detection rate of 85 − 11 + 5 % 85^{+5}_{-11}\% (17/20). This confirms that the [ Ne v ] λ ​ 3426 \lambda 3426 emission line is a strong tracer of AGN activity even in cases of heavy obscuration, in agreement with previous studies;

abstract · abstract

One of JWST's most unexpected discoveries is the emergence of "Little Red Dots'' (LRDs): compact sources at $z \gtrsim 3$ with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest a population of early, unusual active galactic nuclei (AGNs). Using a comprehensive photometric selection and public NIRSpec/PRISM spectroscopy across six JWST deep fields, we identify a large sample of 118 LRDs with high-S/N spectra, enabling a population-wide analysis of their UV-optical continuum and emission lines. We find clear correlations between rest-frame color ([0.3-0.9\,$μ$m]) and slopes: bluer LRDs have blue UV slopes ($β_{ν,\mathrm{UV}} \sim 0.3$) and red optical slopes, while redder LRDs exhibit redder UV slopes ($β_{ν,\mathrm{UV}} \sim 1.1$). The continuum shape shows a similar trend: redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical SEDs. From literature compilations, $\sim$60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission-line diagnostics reveal a shift from high H$_α$/H$_β$ and low [OIII]$\lambda5007$/H$_β$ in redder LRDs to the opposite in bluer ones, along with stronger narrow-line equivalent widths, suggesting a transition from AGN- to host-dominated emission. We fit the spectra with a two-component model combining a gas-enshrouded black hole (BH) and a galaxy host. Redder LRDs require higher-luminosity, unreddened BHs and modestly reddened hosts; bluer LRDs require lower-luminosity, reddened BHs and dust-free galaxies. This framework reproduces the diversity in colors and spectral shape by varying BH luminosity, obscuration, and host-to-BH luminosity ratio.

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Empirical M BH M_{\rm BH} measurements from broad H α \alpha emission ( FWHM ≳ 4000 \mathrm{FWHM}\gtrsim 4000 km s -1 ) place our [NeV]-detected QGs on the local M BH M_{\rm BH} – M ⋆ M_{\star} scaling relation. The bolometric luminosities inferred from [NeV] and [O III ] reach quasar-like values ( L bol = 10 45 − 46 L_{\rm bol}=10^{45-46} erg s -1 ), with Eddington ratios of λ Edd ≈ 10 − 50 \lambda_{\rm Edd}\approx 10-50 % and black hole accretion rates of a few M ⊙ M_{\odot} yr -1 , comparable to or exceeding the residual star formation rates in the most extreme cases.

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Semi-analytical models ( Shark , Gaea ) and zoom-in simulations ( Black Dawn with the Mistral feedback model) broadly reproduce the observed trend of declining AGN activity with time since quenching, consistent with the physical picture emerging from the observations. At peak post-quenching activity, all models produce Eddington ratios of ≈ 10 − 50 \approx 10-50 % and bolometric luminosities broadly consistent with our observed values.