The Population of Type~1 Active Galactic Nuclei in Dark Energy Spectroscopic Instrument. I. Profile-dependent Measurements of the Low-redshift Sample

abstract · abstract

We present a spectral analysis of a large sample of low-redshift type 1 active galactic nuclei (AGNs) selected from the first data release of the Dark Energy Spectroscopic Instrument (DESI DR1). For objects at $z\le0.9$, we perform spectral fitting and ML-assisted refinement, yielding 114,754 type 1 AGNs. We use two fitting schemes that differ only in the broad-line model: the broad Balmer components are fitted with either a Lorentzian function or a sum of Gaussians. The continuum and [O III] luminosity measurements agree closely between the two schemes, whereas the Gaussians scheme generally yields larger broad-H$β$ full width at half maximum (FWHM) values, larger virial black hole masses, and lower accretion rates. The adopted broad-Balmer profile also changes the decomposition of narrow Balmer emission. Specifically, the anti-correlation between [O III]$\lambda5007$/narrow H$β$ and accretion rate is stronger under the Gaussians scheme with a Spearman rank correlation coefficient $r_{\rm s}=-0.412$, than under the Lorentzian scheme with $r_{\rm s}=-0.206$; the same tendency is observed in the narrow-line Seyfert 1 galaxies (NLS1s) subset ($r_{\rm s}=-0.435$ and $-0.259$ for the Gaussians and Lorentzian schemes, respectively), suggesting that the Gaussians scheme may provide a more self-consistent separation of the broad and narrow H$β$ components. Moreover, the consistent correlations recovered under both profile prescriptions favor a continuous type 1 accretion-state sequence, with NLS1s occupying its high-accretion end rather than constituting a distinct population.

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Figure 6: Distributions of the main emission-line measurements and derived physical quantities for the DESI low-redshift broad-H β \beta type 1 AGN sample. The red and blue histograms show the results obtained from the Lorentzian and Gaussians broad-H β \beta fitting schemes, respectively. The panels show, from left to right and from top to bottom, the broad-H β \beta FWHM, broad-H β \beta luminosity, Fe ii strength ℛ Fe \mathcal{R}_{\rm Fe} , narrow H β \beta luminosity, [O iii ] λ ​ 5007 \lambda 5007 luminosity, host-subtracted 5100 Å continuum luminosity, virial black-hole mass, dimensionless accretion rate and reduced χ 2 \chi^{2} . The vertical dashed lines mark the median values of the corresponding distributions. The annotations show the KS statistic D D and its Monte Carlo p p -value, p MC p_{\rm MC} , calibrated using 10,000 paired bootstrap resamples.

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Figure 10: Relations among virial black-hole mass, dimensionless accretion rate, and ℛ Fe \mathcal{R}_{\rm Fe} . The left and right columns show the results from the Lorentzian and Gaussians fitting schemes, respectively. The top row shows the M BH M_{\rm BH} – ℳ ˙ \dot{\mathscr{M}} relation, and the bottom row shows the ℛ Fe \mathcal{R}_{\rm Fe} – ℳ ˙ \dot{\mathscr{M}} relation. Orange points denote the NLS1 subset, while blue points show the full type 1 sample. Black contours represent the density distribution of the full type 1 sample. Spearman rank coefficients for the corresponding samples are shown in each panel.

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The ℛ Fe \mathcal{R}_{\rm Fe} – ℳ ˙ \dot{\mathscr{M}} relation shows a positive correlation in both fitting schemes. For the full type 1 sample, the Spearman coefficient is r s = 0.667 r_{\rm s}=0.667 for the Lorentzian scheme and r s = 0.614 r_{\rm s}=0.614 for the Gaussians scheme. This result is consistent with the commonly discussed connection between strong optical Fe ii emission and high inferred accretion rate. However, ℛ Fe \mathcal{R}_{\rm Fe} is not a single-parameter accretion-rate tracer, because it can also depend on the ionizing SED, gas density, column density, metallicity, microturbulence, and orientation [ 68 , 69 ] . In addition, the ℛ Fe \mathcal{R}_{\rm Fe} – ℳ ˙ \dot{\mathscr{M}} relation is not fully independent of the adopted virial prescription, because ℛ Fe \mathcal{R}_{\rm Fe} enters the adopted R H ​ β R_{\rm H\beta} – L 5100 L_{5100} relation used to estimate M BH M_{\rm BH} and ℳ ˙ \dot{\mathscr{M}} . These additional dependencies may partly explain why the ℛ Fe \mathcal{R}_{\rm Fe} – ℳ ˙ \dot{\mathscr{M}} correlation is weaker than the built-in M BH M_{\rm BH} – ℳ ˙ \dot{\mathscr{M}} anti-correlation for the full type 1 sample. For the NLS1 subset, however, the ℛ Fe \mathcal{R}_{\rm Fe} – ℳ ˙ \dot{\mathscr{M}} correlation is stronger, with r s = 0.689 r_{\rm s}=0.689 and 0.790 0.790 for the Lorentzian and Gaussians schemes, respectively. This may be because, within the low-FWHM occupied by NLS1s, variations in ℛ Fe \mathcal{R}_{\rm Fe} more directly trace differences in the inferred accretion state, while the restricted FWHM range reduces the dynamic range driven by line width alone.

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Figure 11: Relations between the H β \beta equivalent widths and the host-subtracted 5100 Å continuum luminosity. The left and right columns show the results from the Lorentzian and Gaussians fitting schemes, respectively. The upper and lower rows show EW broad ​ H ​ β {}_{\rm broad\,H\beta} and EW narrow ​ H ​ β {}_{\rm narrow\,H\beta} , respectively. Orange points denote NLS1 subset, while blue points represent the full type 1 AGNs. Black contours show the density distribution of the full type 1 sample. Spearman rank coefficients for the corresponding samples are shown in each panel.

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Figure 12: Relation between the [O iii ] λ ​ 5007 \lambda 5007 /narrow H β \beta and the dimensionless accretion rate. The left and right panels show the results from the Lorentzian and Gaussians fitting schemes, respectively. Orange points denote the NLS1 subset, while blue points represent the full type 1 AGNs. Black contours show the density distribution of the full type 1 sample. Spearman rank coefficients for the corresponding samples are shown in each panel.

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We construct a sample of 114,754 low-redshift type 1 AGNs from DESI DR1 through host-galaxy decomposition, emission-line fitting, and ML-assisted sample refinement. Each spectrum is analyzed using both Lorentzian and Gaussians broad-Balmer fitting schemes, while all other spectral components and fitting constraints are treated identically. Our main conclusions are as follows.

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The spectral measurements show clear dependence on the adopted broad-Balmer profile. The distributions show that the Gaussians scheme generally yields larger broad-H β \beta FWHM values than the Lorentzian scheme, especially at the low-FWHM end, and consequently gives larger virial black-hole masses and lower dimensionless accretion rates. The Gaussians scheme also gives larger ℛ Fe \mathcal{R}_{\rm Fe} , while narrow-line ratios involving narrow H β \beta or narrow H α \alpha are generally smaller than those from the Lorentzian scheme because of the different broad–narrow Balmer decomposition. By contrast, the measured broad-H β \beta luminosity and [O iii ] λ ​ 5007 \lambda 5007 luminosity remain comparatively stable between the two schemes.

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The adopted broad-Balmer profile also affects the statistical correlations in the ℛ Fe \mathcal{R}_{\rm Fe} –FWHM plane, the M BH M_{\rm BH} – ℳ ˙ \dot{\mathscr{M}} plane, the ℛ Fe \mathcal{R}_{\rm Fe} – ℳ ˙ \dot{\mathscr{M}} plane, the EW– L 5100 L_{5100} relations, the BPT diagrams, and the [O iii ] λ ​ 5007 \lambda 5007 /narrow H β \beta – ℳ ˙ \dot{\mathscr{M}} relation, with the correlation strengths changing to different degrees. The profile dependence is especially visible in quantities involving narrow Balmer emission, including the [O i ] and [N ii ] BPT diagrams and the [O iii ] λ ​ 5007 \lambda 5007 /narrow H β \beta – ℳ ˙ \dot{\mathscr{M}} relation. For the latter relation, the anti-correlation is substantially stronger in the Gaussians scheme than in the Lorentzian scheme, with Spearman rank correlation coefficients of r s = − 0.409 r_{\rm s}=-0.409 and − 0.207 -0.207 for the full type 1 sample, and r s = − 0.352 r_{\rm s}=-0.352 and − 0.258 -0.258 for the NLS1 subset, respectively. These results favor the Gaussians scheme as a more self-consistent decomposition of the broad and narrow Balmer components.

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Despite these quantitative differences, the main relations are recovered under both fitting schemes. Both fitting schemes reveal a continuous type 1 accretion sequence, whose continuity becomes more apparent in the logarithmic ℛ Fe \mathcal{R}_{\rm Fe} –FWHM plane and along which decreasing broad-H β \beta FWHM is accompanied by stronger optical Fe ii emission and higher accretion rates. Along the same sequence, the [O iii ] λ ​ 5007 \lambda 5007 /narrow H β \beta ratio tends to decrease toward the high- ℳ ˙ \dot{\mathscr{M}} end, indicating that the BLR accretion sequence is accompanied by systematic changes in narrow-line ratios. For the objects classified as NLS1s under both fitting schemes, we find that they do not form a physically distinct population in these diagrams, but instead occupy one end of the continuous type 1 accretion sequence.

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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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As shown in Figure 4 , we find consistent results with the high-redshift LRDs, with most sources showing large ( ≳ 7 \gtrsim 7 ) H α \alpha /H β \beta ratios. Meanwhile, in the parent sample of broad-line AGN with weak [S ii ] and [N ii ], we find a clustering of points near H α \alpha /H β ≈ 3.1 \beta\approx 3.1 . Moreover, the LRDs stand out significantly in terms of their He i EW, similar to the high-redshift sources ( Matthee et al., 2026 ) . Both the low-redshift and high-redshift LRDs display an anti-correlation between the Balmer deecrement and the EW of the HeI line.

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Like J1717+3807, we find evidence for weak and uncorrelated white noise variability, based on the intrinsic scatter σ int = 0.0 − 0.1 \sigma_{\rm int}=0.0-0.1 mag for most sources and small τ DRW \tau_{\rm DRW} for all. In particular for J1717+3807, J0716+5433, J0829+1312, this result holds for hundreds or thousands of observations. While J1502+0250 shows the most potential for significant variability, we are cautious to make such a conclusion given that most of its data points lie below the ZTF limiting magnitude. Moreover, the damping timescale τ DRW \tau_{\rm DRW} for J1502+0250 is much smaller than typical quasar variability (see also Fig. 8 ), indicative of white noise as also shown in the other DESI LRDs. ZTF r-band light curves of the DESI LRDs besides J1717+3807 can be seen in Figure 16 .

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Table 3: Summary of the kinematic dipole measurements obtained from the DESI DR1 tracer samples. The best-fitting dipole direction, given by the Galactic coordinates ( l , b ) (l,b) , and the corresponding 68 % 68\% directional uncertainty Δ ​ θ 68 \Delta\theta_{68} are inferred from the three-dimensional distribution of velocity vectors across the mock realizations. The dipole amplitude is reported as an equivalent peculiar velocity, with 1 ​ σ 1\sigma uncertainties quoted as the 16th and 84th percentiles of the β \beta distribution.

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This result is in excellent agreement with the CMB-inferred value v = 369.82 ± 0.11 ​ km ​ s − 1 v=369.82\pm 0.11\,\mathrm{km\,s^{-1}} , consistent with the expectation that the kinematic contribution dominates the redshift dipole at sufficiently high redshift. This redshift evolution is physically expected. The measured dipole is a combination of the observer’s true kinematic motion and the intrinsic clustering dipole (including local bulk flows). While the kinematic velocity β \beta is a global constant, the contamination from large-scale structure (LSS) and bulk flows decays significantly as the survey volume increases. Therefore, “sufficiently high redshift” is quantitatively defined as the regime (typically z > 0.8 z>0.8 , as probed by the QSO sample) where the cosmic variance of the intrinsic LSS dipole and bulk flows drops well below the kinematic signal of ∼ 370 \sim 370 km s -1 , allowing the kinematic contribution to dominate the measurement.

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The present paper describes results from the first three years of the survey, which will be part of the future data release 2 (DR2). This dataset represents approximately 70% of the complete dark time survey. In addition to the larger area, the typical quasar in DR2 has 2–3 observations, so the spectral SNR per quasar is higher than in DR1. Figure 1 shows the DR2 footprint and SDSS DR16 footprint for comparison.

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The red errorbars show the BAO shifts from alternative analyses that result in small changes of the dataset. These are: λ obs < 5500 \lambda_{\rm obs}<5500 Å : We only use Ly α \alpha pixels below this observed wavelength, rather than the baseline value of λ obs < 5577 \lambda_{\rm obs}<5577 Å; λ obs > 3650 \lambda_{\rm obs}>3650 Å : We only use Ly α \alpha pixels above this observed wavelength, rather than the baseline value of λ obs > 3600 \lambda_{\rm obs}>3600 Å; λ RF < 1200 \lambda_{\rm RF}<1200 Å : We only use Ly α \alpha pixels below this rest-frame wavelength, rather than the baseline value of λ RF < 1205 \lambda_{\rm RF}<1205 Å. z QSO < 3.78 z_{\rm QSO}<3.78 : We only include quasars with z QSO = 3.78 z_{\rm QSO}=3.78 , which is the highest redshift included in the mocks; > 50 >50 pixels in forest : We include lines-of-sight with more than 50 valid Ly α \alpha pixels. For the baseline analysis we require at least 150 pixels; only quasar targets : We only use quasars that were considered quasar targets. This variation causes a more significant change in the size of the dataset as described above; Mask DLAs in spectra with SNR ​ _ ​ RED > 3 {\rm SNR\_RED}>3 DLAs : We only mask DLAs identified in quasar spectra with SNR ​ _ ​ REDSIDE > 3 {\rm SNR\_REDSIDE}>3 , instead of the SNR ​ _ ​ REDSIDE > 2 {\rm SNR\_REDSIDE}>2 threshold used in the baseline analysis; Weak BALs : We do not include the Ly α \alpha forest of those quasars where we have identified very strong BAL features. This only excludes BALs with A ​ I > 840 AI>840 , corresponding to the 50% percentile of strongest BALs [ 73 ] . No sharp lines mask : We do not mask the four sharp lines discussed in [ 28 ] , related to sky lines and Calcium absorption features from the interstellar medium of the Milky Way.

abstract / block 1 · abstract

JWST has revealed a substantial population of "Little Red Dots" (LRDs) at $z>4$, challenging conventional AGN frameworks. However, the low-redshift regime remains largely unexplored. In the second paper of the (LRDs)$^2$ series, we present a systematic selection from DESI DR1 and identify 27 LRDs at $z=0.2-0.9$, yielding a number density lower limit of $7.5 \times 10^{-10}$ cMpc$^{-3}$. We conducted near-IR spectroscopic follow-up observations for 18 of them, revealing their full SED shapes and emission lines. These low-$z$ LRDs share the hallmark properties of their high-$z$ counterparts: compact morphology, V-shaped UV-optical continua, broad Balmer emission with extreme decrements (median H$α$/H$β\sim 16$), frequent Balmer absorption (67%), and blackbody-like optical-to-near-IR continua. All have low metallicity, occupy the same regions in the BPT diagram as high-$z$ LRDs, and have softer ionizing spectra than typical AGNs. The consistency between low-$z$ and high-$z$ LRD properties indicates the same physical processes at work. The correlation between broad-line Balmer luminosity and $L_{5100}$ deviates from that of local type-1 AGNs, limiting the direct application of local BH mass calibrations. Ionized [O III] outflows are ubiquitous (78%). One LRD at $z=0.196$, J1717+3807, shows robust long-term variability in $i$ and WISE bands. The optical-to-NIR continua of LRDs reveal a wide range of temperatures $\sim 2000-4700$ K (peak $0.6-1.5$ $μ$m), with a subset showing cooler and larger envelopes than those at high $z$. Low-$z$ LRDs serve not only as proximate laboratories for probing the nature of LRDs, but also trace the cosmic evolution of this population from the cosmic dawn to the present day.

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We distribute the quasars on a HEALPix grid at N side = 2048 N_{\rm side}=2048 . This results in a convolution of the tracers with a pixel window function, effectively yielding aliasing power. Therefore, the spectra are multiplied by the pixel window w ℓ w_{\ell} using the routine from healpy ’s pixwin function, replacing the theory spectra by C ℓ κ ​ q → w ℓ ​ C ℓ κ ​ q C_{\ell}^{\kappa q}\rightarrow w_{\ell}C_{\ell}^{\kappa q} and C ℓ q ​ q → w ℓ 2 ​ C ℓ q ​ q + SN C_{\ell}^{qq}\rightarrow w^{2}_{\ell}C_{\ell}^{qq}+\mathrm{SN} . Note that (i) the auto-spectra are convolved with the pixel window prior to adding the shot noise; and (ii) the effect of w ℓ 2 w_{\ell}^{2} is approximately 0.8, 1.4, 3.2% for our scale cuts ℓ max = 605 , 805 , 1205 \ell_{\rm max}=605,\,805,\,1205 , respectively. To avoid assuming a fiducial value of the shot noise when accounted for at the data level (see, e.g., [ 27 , 28 ] ), we forward model the pixel window function (similar to [ 37 ] ) and directly apply it to the theory spectra.

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To explore the difference between our analysis and the one presented in Ref. [ 41 ] we fix the higher order biases, magnification bias and shot noise and only sample b 1 b_{1} in addition to the cosmological parameters. The results are shown in Figs. 7 and 9 with this variation denoted by “Linear theory”. We additionally compare the impact of using the DESI DR2 BAO data [ 109 ] . Following baseline expectation, we find tighter constraints when using linear theory which use as scale cut corresponding to the blue contours. Whilst our baseline analysis marginalizes over the higher-order nuisance parameters this comes at a cost of removing shape information. For the growth of structure we find σ 8 = 0.864 ± 0.048 \sigma_{8}=0.864\pm 0.048 [ 0.866 ] [0.866] ( σ 8 = 0.862 ± 0.047 \sigma_{8}=0.862\pm 0.047 [ 0.859 ] [0.859] ) using a DESI DR1 (DR2) BAO prior. This corresponds to a discrepancy of − 0.99 ​ σ -0.99\sigma ( − 0.97 ​ σ -0.97\sigma ). For S 8 S_{8} we find S 8 = 0.859 ± 0.048 S_{8}=0.859\pm 0.048 [ 0.863 ] [0.863] ( S 8 = 0.859 ± 0.048 S_{8}=0.859\pm 0.048 [ 0.855 ] [0.855] ) a − 1.08 ​ σ -1.08\sigma ( − 1.10 ​ σ -1.10\sigma ) difference. For the linear bias parameters we obtain b 1 ​ ( z 1 ) = 2.21 ± 0.15 b_{1}(z_{1})=2.21\pm 0.15 [ 2.2 ] [2.2] b 1 ​ ( z 2 ) = 2.86 − 0.19 + 0.17 b_{1}(z_{2})=2.86^{+0.17}_{-0.19} [ 2.88 ] [2.88] and b 1 ​ ( z 3 ) = 3.43 − 0.26 + 0.23 b_{1}(z_{3})=3.43^{+0.23}_{-0.26} [ 3.45 ] [3.45] which are in somewhat better agreement, i.e. ( 0.21 , 2.57 , 3.49 ) ​ σ (0.21,\,2.57,\,3.49)\sigma , with the values from Eq. ( 14 ) measured from the 3D clustering of DESI DR1 quasars [ 65 ] and the values obtained from our fiducial analysis given in Eq. ( 17 ). The DR2 constraints are within ∼ < 0.05 ​ σ \lower 2.15277pt\hbox{$\;\mathrel{\mathop{\kern 0.0pt\sim}\limits^{<}}\;$}0.05\sigma . The constraining power of this “linear theory” analysis is in better agreement with that of [ 41 ] , with a ∼ 5.5 % \sim 5.5\% constraint on S 8 S_{8} for our linear theory fits compared to a 5.1% constraint on S 8 S_{8} in [ 41 ] . Given the similar detection significances of C ℓ g ​ g C_{\ell}^{gg} and C ℓ κ ​ g C_{\ell}^{\kappa g} in [ 41 ] (21.7 σ \sigma

TeX section 7 / block 1 · tex

results Applying the selection procedure described in Section <ref>, we identify 1,993 N-loud quasars from the DESI DR1 quasar catalog over the redshift range 1.6<z<4.3, corresponding to about 1.2% of the parent sample. The resulting catalog is presented in Table <ref>, including the source identifiers, coordinates, redshifts, continuum properties, major broad line measurements, and additional quantities derived from the spectral fitting. In this section, we first summarize the sample composition and its distribution in redshift and luminosity (Section <ref>). We then examine the spectral properties of the N-loud quasars, including their nitrogen line properties, composite spectrum, and broad line properties relative to normal quasars (Section <ref>). Finally, we compare their single-epoch virial black hole masses and Eddington ratios with those of normal quasars (Section <ref>) and summarize their radio properties (Section <ref>).

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Summary We present a sample of 1,993 DESI DR1 quasars with strong broad and/or emission lines at 1.6<z<4.3, corresponding to about 1.2% of the parent quasar sample. The following points summarize our main findings: * The N-loud quasars have a L_1450 distribution broadly similar to that of the DESI parent sample, but their redshift distribution differs from that of the parent sample. They are more concentrated around z∼2.5–3, and the observed N-loud fraction reaches a peak of about 2% near this redshift range. * The composite spectrum of the N-loud quasars has a broadly similar UV continuum shape to that of the parent quasars, while showing enhanced broad nitrogen emission lines, including , , and . Other metal emission features also show a moderate enhancement. * Relative to a control sample matched in redshift and UV continuum luminosity, the N-loud quasars systematically show narrower broad and emission lines, lower single-epoch virial black hole masses, and higher Eddington ratios. These tendencies are also seen in comparison with the parent quasar sample. Relative to the matched control sample, the median log M_ BH of the N-loud quasars is lower by about 0.25 dex, while the median logλ_ Edd is higher by about 0.3 dex. * The radio-loud fraction of the N-loud quasars is 10.1%, with the highest fraction found in objects showing both and emission. Overall, these results indicate that N-loud quasars do not simply represent a small number of extreme objects in the distribution of nitrogen line strength, but instead show a set of correlated systematic properties, including a non-uniform redshift distribution, narrower broad emission lines, lower single-epoch virial black hole masses, higher Eddington ratios, and a non-negligible radio-loud subgroup. These properties suggest that N-loud quasars may preferentially appear during a relatively rapid black hole accretion phase. The consistent enhancement of multiple broad nitrogen emission lines also suggests that nitrogen enhancement is part of the overall UV spectral properties of these objects, rather than an isolated anomaly in a single line. The DESI N-loud quasar catalog presented here provides a large statistical

abstract · abstract

We present a study on the possible overestimation of single-epoch supermassive black hole (SMBH) masses in previous works, based on more than 55,000 type 1 quasars at $0.25 < z < 0.8$ from the Dark Energy Spectroscopic Instrument (DESI). We confirm that iron emission strength serves as a good tracer of the Eddington ratio, and estimate SMBH masses using an iron-corrected $R$-$L$ relation for H$β$, where $R$ is the broad line region size and $L$ is the continuum luminosity. Compared to our measurements, previous canonical measurements without the iron correction are overestimated by a factor of 1.5 on average. The overestimation can be up to a factor of 5 for super-Eddington quasars. The fraction of super-Eddington quasars in our sample is about 5%, significantly higher than 0.4% derived from the canonical measurements. Using a sample featuring both H$β$ and MgII emission lines, we calibrate MgII-based SMBH masses using iron-corrected, H$β$-based SMBH masses and establish an iron-corrected $R$-$L$ relation for MgII. The new relation adds an extra term of $-0.34R_{\mathrm{Fe}}$ to the $R$-$L$ relation, where $R_{\mathrm{Fe}}$ denotes the relative iron strength. We use this formula to build a catalog of about 0.5 million DESI quasars at $0.6<z<1.6$. If these iron-corrected $R$-$L$ relations for H$β$ and MgII are valid at high redshift, current mass measurements of luminous quasars at $z\ge6$ would have been overestimated by a factor of 2.3 on average, alleviating the tension between SMBH mass and growth history in the early universe.