Red quasars are intrinsically X-ray weak with low alpha_OX values, tracing a distinct evolutionary stage of suppressed black hole accretion relative to stellar mass growth.
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abstract
We present an updated and revised analysis of the relationship between the Hbeta broad-line region (BLR) radius and the luminosity of the active galactic nucleus (AGN). Specifically, we have carried out two-dimensional surface brightness decompositions of the host galaxies of 9 new AGNs imaged with the Hubble Space Telescope Wide Field Camera 3. The surface brightness decompositions allow us to create "AGN-free" images of the galaxies, from which we measure the starlight contribution to the optical luminosity measured through the ground-based spectroscopic aperture. We also incorporate 20 new reverberation-mapping measurements of the Hbeta time lag, which is assumed to yield the average Hbeta BLR radius. The final sample includes 41 AGNs covering four orders of magnitude in luminosity. The additions and updates incorporated here primarily affect the low-luminosity end of the R-L relationship. The best fit to the relationship using a Bayesian analysis finds a slope of alpha = 0.533 (+0.035/-0.033), consistent with previous work and with simple photoionization arguments. Only two AGNs appear to be outliers from the relationship, but both of them have monitoring light curves that raise doubt regarding the accuracy of their reported time lags. The scatter around the relationship is found to be 0.19(+/-0.02) dex, but would be decreased to 0.13 dex by the removal of these two suspect measurements. A large fraction of the remaining scatter in the relationship is likely due to the inaccurate distances to the AGN host galaxies. Our results help support the possibility that the R-L relationship could potentially be used to turn the BLRs of AGNs into standardizable candles. This would allow the cosmological expansion of the Universe to be probed by a separate population of objects, and over a larger range of redshifts.
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representative citing papers
Blind tests on simulated disc-wind BLR data show standard RM methods recover rotation but miss wind geometry and yield inconsistent velocity-delay maps despite good spectral fits.
A changing-look AGN exhibits a rapid accretion-driven spectral transition with broad-line region temperatures of approximately 11,800 K measured via Boltzmann plots and stable black hole mass estimates of 5 times 10 to the 7 solar masses across epochs.
A theoretical model of a magnetized black hole envelope is developed to explain the broad emission lines and X-ray faintness observed in little red dots using co-rotating plasma clumps and limited X-ray sources.
Optical-MIR lags of 39.1 days and 79.4 days are measured in Mrk 42 and Mrk 493, yielding dust reverberation radii of 0.032 pc and 0.065 pc with R_dust/R_BLR ratios of approximately 6-7.
Low-luminosity AGN exhibit optical variability structure function slopes that increase with black hole mass from ~0.1 to ~0.3, with amplitude anticorrelated with luminosity, no breaks observed, and variability continuing to rise on 20-year timescales.
Elliptical BLR geometries cause the virial factor f to vary by over an order of magnitude and induce ~0.18 dex scatter in the R-L relation, challenging attributions of RM uncertainties to non-virial motions or radiation pressure.
Using ray-tracing simulations and simulation-based inference, the authors construct an AGN population that reproduces the cosmic X-ray background, number counts, and absorption properties, deriving an intrinsic Compton-thick fraction of 40±3%.
Mid-infrared lines near Sgr A* exhibit no detectable variability during flares, because light-crossing and recombination timescales in the extended gas suppress responses, so the lines cannot constrain instantaneous UV flux.
HE 1237-2252 exhibits a changing-look event driven by intrinsic accretion-rate variations, revealing a two-component broad-line region consisting of virialized gas at ~27 light-days and disk emission at larger radii.
2MASX J0413-0050 transitioned from a narrow-line Seyfert 1 to a Seyfert 1.9 and back while remaining in a high accretion state, supporting classification as a changing-state AGN.
A statistically significant positive correlation (r ~ 0.12-0.13) exists between the absolute velocity offset of broad Hβ lines and dust reddening in quasars, consistent with a population of recoiling black holes.
Multi-epoch spectroscopy of UNAM-KIAS 613 shows transient double-peaked broad Hα emission interpreted as a one-time bipolar outflow in an isolated low-luminosity AGN with Eddington ratio ~0.03-0.04.
Reverberation lags in Mrk 817 range 3-8 days, exceed thin-disk models by factors of 3-6, follow a λ^{4/3} trend with the ICCF method, and vary by up to a factor of 2 between epochs.
A review summarizing detection methods, population statistics, and coevolution of supermassive black holes with host galaxies from early universe observations and simulations.
citing papers explorer
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SDSS-V: Revealing a weak accretion state in X-ray selected red quasars
Red quasars are intrinsically X-ray weak with low alpha_OX values, tracing a distinct evolutionary stage of suppressed black hole accretion relative to stellar mass growth.
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Do Reverberation Mapping Analyses Provide an Accurate Picture of the Broad Line Region?
Blind tests on simulated disc-wind BLR data show standard RM methods recover rotation but miss wind geometry and yield inconsistent velocity-delay maps despite good spectral fits.
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Tracing Active Galactic Nuclei Properties Through a Changing-look Event
A changing-look AGN exhibits a rapid accretion-driven spectral transition with broad-line region temperatures of approximately 11,800 K measured via Boltzmann plots and stable black hole mass estimates of 5 times 10 to the 7 solar masses across epochs.
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A Magnetized Black Hole Envelope Model for Little Red Dots
A theoretical model of a magnetized black hole envelope is developed to explain the broad emission lines and X-ray faintness observed in little red dots using co-rotating plasma clumps and limited X-ray sources.
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The 2MIG isolated AGNs. 3. Optical--IR variability and dust reverberation in the NLSy1 galaxies Mrk~42 and Mrk~493
Optical-MIR lags of 39.1 days and 79.4 days are measured in Mrk 42 and Mrk 493, yielding dust reverberation radii of 0.032 pc and 0.065 pc with R_dust/R_BLR ratios of approximately 6-7.
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Optical Variability Structure Function of Low-Luminosity AGN using ATLAS Lightcurves
Low-luminosity AGN exhibit optical variability structure function slopes that increase with black hole mass from ~0.1 to ~0.3, with amplitude anticorrelated with luminosity, no breaks observed, and variability continuing to rise on 20-year timescales.
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The Impact of Elliptical Broad-Line Regions on Reverberation-Based Black Hole Mass Estimates
Elliptical BLR geometries cause the virial factor f to vary by over an order of magnitude and induce ~0.18 dex scatter in the R-L relation, challenging attributions of RM uncertainties to non-virial motions or radiation pressure.
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Population synthesis of active galactic nuclei based on the radiation-regulated unification model
Using ray-tracing simulations and simulation-based inference, the authors construct an AGN population that reproduces the cosmic X-ray background, number counts, and absorption properties, deriving an intrinsic Compton-thick fraction of 40±3%.
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Infrared Line Diagnostics Fail to Constrain Sgr A*'s UV Output
Mid-infrared lines near Sgr A* exhibit no detectable variability during flares, because light-crossing and recombination timescales in the extended gas suppress responses, so the lines cannot constrain instantaneous UV flux.
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A Changing-Look Seyfert Discovered by eROSITA Reveals a Two-Component Broad-Line Region
HE 1237-2252 exhibits a changing-look event driven by intrinsic accretion-rate variations, revealing a two-component broad-line region consisting of virialized gas at ~27 light-days and disk emission at larger radii.
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An X-ray and optical spectral study of the changing-look narrow-line Seyfert 1 2MASX J0413-0050
2MASX J0413-0050 transitioned from a narrow-line Seyfert 1 to a Seyfert 1.9 and back while remaining in a high accretion state, supporting classification as a changing-state AGN.
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Statistical evidence for massive black hole recoils in active galactic nuclei
A statistically significant positive correlation (r ~ 0.12-0.13) exists between the absolute velocity offset of broad Hβ lines and dust reddening in quasars, consistent with a population of recoiling black holes.
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Spectral Evolution and Transient Broad-Line Features in the Isolated AGN UNAM-KIAS 613
Multi-epoch spectroscopy of UNAM-KIAS 613 shows transient double-peaked broad Hα emission interpreted as a one-time bipolar outflow in an isolated low-luminosity AGN with Eddington ratio ~0.03-0.04.
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AGN STORM 2. XII. Ground-Based Optical Photometry and Lag Measurements of Mrk 817
Reverberation lags in Mrk 817 range 3-8 days, exceed thin-disk models by factors of 3-6, follow a λ^{4/3} trend with the ICCF method, and vary by up to a factor of 2 between epochs.
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