arXiv subjects

Marianne Vestergaard

Publications and source records attributed to Marianne Vestergaard.

At least 37 records · Page 2Linked to original sources

arXiv2025

Kinematic misalignment as a driver of black hole activity in galaxies with external interactions

The process of Active Galactic Nuclei (AGN) fuelling relies on the transport of gas across several orders of magnitude in physical scale until the gas reaches the supermassive black hole at the centre of a galaxy. This work explores the role of kinematically misaligned gas in the fuelling of AGN in a sample of 4769 local galaxies from the MaNGA survey. We investigate for the first time the relative role of external interactions and the presence of kinematic misalignment as mechanisms to explain the observed increase in AGN fraction in galaxies with large stellar to gas kinematic misalignment ($>$45 degrees). Using a sample of galaxies with evidence of recent external interactions we find that there is a significantly higher fraction of AGN in those where a large stellar to gas kinematic misalignment is observed (20$^{+6}_{-4}\%$) compared with 6.2$^{+0.6}_{-0.5}\%$ in galaxies where no kinematic misalignment is observed. We determine that gas to stellar misalignment has an important role in the fraction of AGN observed, increasing the AGN fraction beyond the potential effect of external interactions. This result demonstrates the importance of misaligned structures to the fuelling of supermassive black holes.

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arXiv2025

Flares in the Changing Look AGN Mrk 590. II: Deep X-ray observations reveal a Comptonizing inner accretion flow

Mrk 590 is a Changing Look AGN currently in an unusual repeat X-ray and UV flaring state. Here, we report on deep X-ray observations with XMM-Newton, NuSTAR, and NICER, obtained at a range of X-ray flux levels. We detect a prominent soft excess below 2 keV; its flux is tightly correlated with that of both the X-ray and UV continuum, and it persists at the lowest flux levels captured. Our Bayesian model comparison strongly favors inverse Comptonization as the origin of this soft excess, instead of blurred reflection. We find only weak reflection features, with R~0.4 assuming Compton-thick reflection. Most of this reprocessing occurs at least $\sim$800 gravitational radii (roughly three light-days) from the continuum source. Relativistically broadened emission is weak or absent, suggesting the lack of a standard `thin disk' at small radii. We confirm that the predicted broad-band emission due to Comptonization is roughly consistent with the observed UV--optical photometry. This implies an optically thick, warm ($kT_e\sim0.3$ keV) scattering region that extends to at least $\sim10^3$ gravitational radii, reprocessing any UV thermal emission. The lack of a standard `thin disk' may also explain the puzzling $\sim3$-day X-ray to UV delay previously measured for Mrk 590. Overall, we find that the X-ray spectral changes in Mrk 590 are minimal, despite substantial luminosity changes. Other well-studied changing look AGN display more dramatic spectral evolution, e.g., disappearing continuum or soft excess. This suggests that a diversity of physical mechanisms in the inner accretion flow may produce a UV--optical changing-look event.

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arXiv2024

AGN STORM 2. VII. A Frequency-resolved Map of the Accretion Disk in Mrk 817: Simultaneous X-ray Reverberation and UVOIR Disk Reprocessing Time Lags

X-ray reverberation mapping is a powerful technique for probing the innermost accretion disk, whereas continuum reverberation mapping in the UV, optical, and infrared (UVOIR) reveals reprocessing by the rest of the accretion disk and broad-line region (BLR). We present the time lags of Mrk 817 as a function of temporal frequency measured from 14 months of high-cadence monitoring from Swift and ground-based telescopes, in addition to an XMM-Newton observation, as part of the AGN STORM 2 campaign. The XMM-Newton lags reveal the first detection of a soft lag in this source, consistent with reverberation from the innermost accretion flow. These results mark the first simultaneous measurement of X-ray reverberation and UVOIR disk reprocessing lags$\unicode{x2013}$effectively allowing us to map the entire accretion disk surrounding the black hole. Similar to previous continuum reverberation mapping campaigns, the UVOIR time lags arising at low temporal frequencies are longer than those expected from standard disk reprocessing by a factor of 2-3. The lags agree with the anticipated disk reverberation lags when isolating short-timescale variability, namely timescales shorter than the H$β$ lag. Modeling the lags requires additional reprocessing constrained at a radius consistent with the BLR size scale inferred from contemporaneous H$β$-lag measurements. When we divide the campaign light curves, the UVOIR lags show substantial variations, with longer lags measured when obscuration from an ionized outflow is greatest. We suggest that, when the obscurer is strongest, reprocessing by the BLR elongates the lags most significantly. As the wind weakens, the lags are dominated by shorter accretion disk lags.

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arXiv2024

AGN STORM 2: VIII. Investigating the Narrow Absorption Lines in Mrk 817 Using HST-COS Observations

We observed the Seyfert 1 galaxy Mrk817 during an intensive multi-wavelength reverberation mapping campaign for 16 months. Here, we examine the behavior of narrow UV absorption lines seen in HST/COS spectra, both during the campaign and in other epochs extending over 14 years. We conclude that while the narrow absorption outflow system (at -3750 km/s with FWHM=177 km/s) responds to the variations of the UV continuum as modified by the X-ray obscurer, its total column density (logNH =19.5 cm-2) did not change across all epochs. The adjusted ionization parameter (scaled with respect to the variations in the Hydrogen ionizing continuum flux) is log UH =-1.0. The outflow is located at a distance smaller than 38 parsecs from the central source, which implies a hydrogen density of nH > 3000 cm-3. The absorption outflow system only covers the continuum emission source and not the broad emission line region, which suggests that its transverse size is small (< 1e16 cm), with potential cloud geometries ranging from spherical to elongated along the line of sight.

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arXiv2024

AGN STORM 2: IX. Studying the Dynamics of the Ionized Obscurer in Mrk 817 with High-resolution X-ray Spectroscopy

We present the results of the XMM-Newton and NuSTAR observations taken as part of the ongoing, intensive multi-wavelength monitoring program of the Seyfert 1 galaxy Mrk 817 by the AGN Space Telescope and Optical Reverberation Mapping 2 (AGN STORM 2) Project. The campaign revealed an unexpected and transient obscuring outflow, never before seen in this source. Of our four XMM-Newton/NuSTAR epochs, one fortuitously taken during a bright X-ray state has strong narrow absorption lines in the high-resolution grating spectra. From these absorption features, we determine that the obscurer is in fact a multi-phase ionized wind with an outflow velocity of $\sim$5200 km s$^{-1}$, and for the first time find evidence for a lower ionization component with the same velocity observed in absorption features in the contemporaneous HST spectra. This indicates that the UV absorption troughs may be due to dense clumps embedded in diffuse, higher ionization gas responsible for the X-ray absorption lines of the same velocity. We observe variability in the shape of the absorption lines on timescales of hours, placing the variable component at roughly 1000 $R_g$ if attributed to transverse motion along the line of sight. This estimate aligns with independent UV measurements of the distance to the obscurer suggesting an accretion disk wind at the inner broad line region. We estimate that it takes roughly 200 days for the outflow to travel from the disk to our line of sight, consistent with the timescale of the outflow's column density variations throughout the campaign.

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arXiv2024

A quasar-galaxy merger at $z\sim 6.2$: rapid host growth via accretion of two massive satellite galaxies

We present JWST/NIRSpec Integral Field Spectroscopy in the rest-frame optical bands of the system PJ308-21, a quasar at $z=6.2342$ caught as its host galaxy interacts with companion galaxies. We detect spatially extended emission of several emission lines (H$α$, H$β$, [OIII], [NII], [SII], HeII), which we use to study the properties of the ionized phase of the interstellar medium: the source and hardness of the photoionizing radiation field, metallicity, dust reddening, electron density and temperature, and star formation. We also marginally detect continuum starlight emission associated with the companion sources. We find that at least two independent satellite galaxies are part of the system. While the quasar host appears highly enriched and obscured, with AGN-like photoionization conditions, the western companion shows minimal dust extinction, low metallicity ($Z\sim0.4$ Z$_\odot$), and star-formation driven photoionization. The eastern companion shows higher extinction and metallicity ($Z\sim0.8$ Z$_\odot$) compared to the western companion, and it is at least partially photoionized by the nearby quasar. We do not find any indication of AGN in the companion sources. Our study shows that while the quasar host galaxy is already very massive ($M_{\rm dyn}>10^{11}$ M$_\odot$), it is still rapidly building up by accreting two relatively massive ($M_{\rm star}\sim 10^{10}$ M$_\odot$) companion sources. This dataset showcases the power of JWST in exposing the build-up of massive galaxies in the first Gyr of the Universe.

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arXiv2024

A quasar-galaxy merger at $z\sim6.2$: black hole mass and quasar properties from the NIRSpec spectrum

We present JWST/NIRSpec integral field data of the quasar PJ308-21 at $z=6.2342$. As shown by previous ALMA and HST imaging, the quasar has two companion sources, interacting with the quasar host galaxy. The high-resolution G395H/290LP NIRSpec spectrum covers the $2.87-5.27\ \rm μm$ wavelength range and shows the rest-frame optical emission of the quasar with exquisite quality ($S/N\sim 100-400$ per spectral element). Based on the H$β$ line from the broad line region, we obtain an estimate of the black hole mass $M_{\rm BH,Hβ}\sim 2.7\times 10^{9}\ \rm M_{\odot}$. This value is within a factor $\lesssim 1.5$ of the H$α$-based black hole mass from the same spectrum ($M_{\rm BH, Hα}\sim 1.93\times 10^{9}\ \rm M_{\odot}$) and is consistent with a previous estimate relying on the MgII $λ2799$ ($M_{\rm BH, MgII}\sim 2.65\times 10^{9}\ \rm M_{\odot}$). All these $M_{\rm BH}$ are within the $\sim 0.5$ dex intrinsic scatter of the adopted mass calibrations. The high Eddington ratio of PJ308-21 $λ_{\rm Edd,Hβ}\sim 0.67$ ($λ_{\rm Edd,Hα}\sim 0.96$) is in line with the overall quasar population at $z \gtrsim 6$. The relative strengths of the [OIII], FeII and H$β$ lines are consistent with the empirical "Eigenvector 1" correlations as observed for low redshift quasars. We find evidence for blueshifted [OIII] $λ5007$ emission with a velocity offset $Δv_{\rm [OIII]}=-1922\pm 39$ km s$^{-1}$ from the systemic velocity and a $\rm FWHM([OIII])=2776^{+75}_{-74}$ km s$^{-1}$. This may be the signature of an outflow from the nuclear region, despite the true values of $Δv_{\rm [OIII]}$ and $\rm FWHM([OIII])$ are likely more uncertain due to the blending with H$β$ and FeII lines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.

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arXiv2024

AGN STORM 2: V. Anomalous Behavior of the CIV Light Curve in Mrk 817

An intensive reverberation mapping campaign on the Seyfert 1 galaxy Mrk817 using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) revealed significant variations in the response of the broad UV emission lines to fluctuations in the continuum emission. The response of the prominent UV emission lines changes over a $\sim$60-day duration, resulting in distinctly different time lags in the various segments of the light curve over the 14 months observing campaign. One-dimensional echo-mapping models fit these variations if a slowly varying background is included for each emission line. These variations are more evident in the CIV light curve, which is the line least affected by intrinsic absorption in Mrk817 and least blended with neighboring emission lines. We identify five temporal windows with distinct emission line response, and measure their corresponding time delays, which range from 2 to 13 days. These temporal windows are plausibly linked to changes in the UV and X-ray obscuration occurring during these same intervals. The shortest time lags occur during periods with diminishing obscuration, whereas the longest lags occur during periods with rising obscuration. We propose that the obscuring outflow shields the ultraviolet broad lines from the ionizing continuum. The resulting change in the spectral energy distribution of the ionizing continuum, as seen by clouds at a range of distances from the nucleus, is responsible for the changes in the line response.

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arXiv2023

AGN STORM 2. VI. Mapping Temperature Fluctuations in the Accretion Disk of Mrk 817

We fit the UV/optical lightcurves of the Seyfert 1 galaxy Mrk 817 to produce maps of the accretion disk temperature fluctuations $δT$ resolved in time and radius. The $δT$ maps are dominated by coherent radial structures that move slowly ($v \ll c$) inwards and outwards, which conflicts with the idea that disk variability is driven only by reverberation. Instead, these slow-moving temperature fluctuations are likely due to variability intrinsic to the disk. We test how modifying the input lightcurves by smoothing and subtracting them changes the resulting $δT$ maps and find that most of the temperature fluctuations exist over relatively long timescales ($\sim$100s of days). We show how detrending AGN lightcurves can be used to separate the flux variations driven by the slow-moving temperature fluctuations from those driven by reverberation. We also simulate contamination of the continuum emission from the disk by continuum emission from the broad line region (BLR), which is expected to have spectral features localized in wavelength, such as the Balmer break contaminating the $U$ band. We find that a disk with a smooth temperature profile cannot produce a signal localized in wavelength and that any BLR contamination should appear as residuals in our model lightcurves. Given the observed residuals, we estimate that only $\sim$20% of the variable flux in the $U$ and $u$ lightcurves can be due to BLR contamination. Finally, we discus how these maps not only describe the data, but can make predictions about other aspects of AGN variability.

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arXiv2023

AGN STORM 2. IV. Swift X-ray and ultraviolet/optical monitoring of Mrk 817

The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble UV continuum light curves, we measure interband continuum lags, $τ(λ)$, that increase with increasing wavelength roughly following $τ(λ) \propto λ^{4/3}$, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve - the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad line region gas that sees an absorbed ionizing continuum.

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arXiv2023

Detection of stellar light from quasar host galaxies at redshifts above 6

The detection of starlight from the host galaxies of quasars during the reionization epoch ($z>6$) has been elusive, even with deep HST observations. The current highest redshift quasar host detected, at $z=4.5$, required the magnifying effect of a foreground lensing galaxy. Low-luminosity quasars from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) mitigate the challenge of detecting their underlying, previously-undetected host galaxies. Here we report rest-frame optical images and spectroscopy of two HSC-SSP quasars at $z>6$ with JWST. Using NIRCam imaging at 3.6$μ$m and 1.5$μ$m and subtracting the light from the unresolved quasars, we find that the host galaxies are massive (stellar masses of $13\times$ and $3.4\times$ $10^{10}$ M$_{\odot}$, respectively), compact, and disk-like. NIRSpec medium-resolution spectroscopy shows stellar absorption lines in the more massive quasar, confirming the detection of the host. Velocity-broadened gas in the vicinity of these quasars enables measurements of their black hole masses ($1.4\times 10^9$ and $2.0\times$ $10^{8}$ M$_{\odot}$, respectively). Their location in the black hole mass - stellar mass plane is consistent with the distribution at low redshift, suggesting that the relation between black holes and their host galaxies was already in place less than a billion years after the Big Bang.

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arXiv2023

Massive black holes in galactic nuclei: Observations

Since a black hole does not emit light from its interior, nor does it have a surface on which light from nearby sources can be reflected, observational study of black hole physics requires observing the gravitational impact of the black hole on its surroundings. A massive black hole leaves a dynamical imprint on stars and gas close by. Gas in the immediate vicinity of an accreting massive black hole can, due to the presence of the black hole, shine so brightly that it outshines the light of the billions of stars in its host galaxy and be detected across the Universe. By observing the emission from stars and gas and determining their kinematics scientists can extract vital information not only on the fundamental properties of the black holes themselves but also the impact they have on their surroundings. As it turns out, supermassive black holes appear to play a vital role in shaping the Universe as we know it, as they can profoundly impact the star formation history in galaxies. As a consequence, these black holes indirectly impact the cosmic build up of chemical elements heavier than Helium and thus affect when and where life can form. For these reasons alone, observations of massive black holes constitute a very active research area of modern astrophysics. In this chapter we aim to provide a general overview -- fit for a non-expert -- of what scientists have learned, and hope to learn, from analyzing observations of massive black holes and the material around them.

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arXiv2023

A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): A First Look at the Rest-frame Optical Spectra of $z > 6.5$ Quasars Using JWST

Studies of rest-frame optical emission in quasars at $z>6$ have historically been limited by the wavelengths accessible by ground-based telescopes. The James Webb Space Telescope (JWST) now offers the opportunity to probe this emission deep into the reionization epoch. We report the observations of eight quasars at $z>6.5$ using the JWST/NIRCam Wide Field Slitless Spectroscopy, as a part of the ''A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE)" program. Our JWST spectra cover the quasars' emission between rest frame $\sim$ 4100 and 5100 Å. The profiles of these quasars' broad H$β$ emission lines span a FWHM from 3000 to 6000 $\rm{km~s^{-1}}$. The H$β$-based virial black hole (BH) masses, ranging from 0.6 to 2.1 billion solar masses, are generally consistent with their MgII-based BH masses. The new measurements based on the more reliable H$β$ tracer thus confirm the existence of billion solar-mass BHs in the reionization epoch. In the observed [OIII] $λλ$4960,5008 doublets of these luminous quasars, broad components are more common than narrow core components ($\le~1200~\rm{km~s^{-1}}$), and only one quasar shows stronger narrow components than broad. Two quasars exhibit significantly broad and blueshifted [OIII] emission, thought to trace galactic-scale outflows, with median velocities of $-610~\rm{km~s^{-1}}$ and $-1430~\rm{km~s^{-1}}$ relative to the [CII] $158\,μ$m line. All eight quasars show strong optical FeII emission, and follow the Eigenvector 1 relations defined by low-redshift quasars. The entire ASPIRE program will eventually cover 25 quasars and provide a statistical sample for the studies of the BHs and quasar spectral properties.

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arXiv2023

AGN STORM 2. III. A NICER view of the variable X-ray obscurer in Mrk 817

The AGN STORM 2 collaboration targeted the Seyfert 1 galaxy Mrk 817 for a year-long multiwavelength, coordinated reverberation mapping campaign including HST, Swift, XMM-Newton, NICER, and ground-based observatories. Early observations with NICER and XMM revealed an X-ray state ten times fainter than historical observations, consistent with the presence of a new dust-free, ionized obscurer. The following analysis of NICER spectra attributes variability in the observed X-ray flux to changes in both the column density of the obscurer by at least one order of magnitude ($N_\mathrm{H}$ ranges from $2.85\substack{+0.48\\ -0.33} \times 10^{22}\text{ cm}^{-2}$ to $25.6\substack{+3.0\\ -3.5} \times 10^{22} \text{ cm}^{-2}$) and the intrinsic continuum brightness (the unobscured flux ranges from $10^{-11.8}$ to $10^{-10.5}$ erg s$^{-1}$ cm$^{-2}$ ). While the X-ray flux generally remains in a faint state, there is one large flare during which Mrk 817 returns to its historical mean flux. The obscuring gas is still present at lower column density during the flare but it also becomes highly ionized, increasing its transparency. Correlation between the column density of the X-ray obscurer and the strength of UV broad absorption lines suggests that the X-ray and UV continua are both affected by the same obscuration, consistent with a clumpy disk wind launched from the inner broad line region.

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arXiv2023

AGN STORM 2: II. Ultraviolet Observations of Mrk817 with the Cosmic Origins Spectrograph on the Hubble Space Telescope

We present reverberation mapping measurements for the prominent ultraviolet broad emission lines of the active galactic nucleus Mrk817 using 165 spectra obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our ultraviolet observations are accompanied by X-ray, optical, and near-infrared observations as part of the AGN Space Telescope and Optical Reverberation Mapping Program 2 (AGN STORM 2). Using the cross-correlation lag analysis method, we find significant correlated variations in the continuum and emission-line light curves. We measure rest-frame delayed responses between the far-ultraviolet continuum at 1180 A and Ly$α$ $\lambda1215$ A ($10.4_{-1.4}^{+1.6}$ days), N V $\lambda1240$ A ($15.5_{-4.8}^{+1.0}$days), SiIV + OIV] $\lambda1397$ A ($8.2_{-1.4}^{+1.4}$ days), CIV $\lambda1549$ A ($11.8_{-2.8}^{+3.0}$ days), and HeII $\lambda1640$ A ($9.0_{-1.9}^{+4.5}$ days) using segments of the emission-line profile that are unaffected by absorption and blending, which results in sampling different velocity ranges for each line. However, we find that the emission-line responses to continuum variations are more complex than a simple smoothed, shifted, and scaled version of the continuum light curve. We also measure velocity-resolved lags for the Ly$α$, and CIV emission lines. The lag profile in the blue wing of Ly$α$ is consistent with virial motion, with longer lags dominating at lower velocities, and shorter lags at higher velocities. The CIV lag profile shows the signature of a thick rotating disk, with the shortest lags in the wings, local peaks at $\pm$ 1500 $\rm km\,s^{-1}$, and a local minimum at line center. The other emission lines are dominated by broad absorption lines and blending with adjacent emission lines. These require detailed models, and will be presented in future work.

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arXiv2023

An increase in black hole activity in galaxies with kinematically misaligned gas

External accretion events such as a galaxy merger or the accretion of gas from the immediate environment of a galaxy, can create a large misalignment between the gas and the stellar kinematics. Numerical simulations have suggested that misaligned structures may promote the inflow of gas to the nucleus of the galaxy and the accretion of gas by the central supermassive black hole. We show for the first time that galaxies with a strong misalignment between the ionised gas and stellar kinematic angles have a higher observed fraction of active black holes than galaxies with aligned rotation of gas and stars. The increase in black hole activity suggests that the process of formation and/or presence of misaligned structures is connected with the fuelling of active supermassive black holes.

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arXiv2023

Flares in the changing look AGN Mrk 590. I: The UV response to X-ray outbursts suggests a more complex reprocessing geometry than a standard disk

Mrk 590 is a known changing-look AGN which almost turned off in 2012, and then in 2017 partially re-ignited into a repeat flaring state, unusual for an AGN. Our \emph{Swift} observations since 2013 allow us to characterise the accretion-generated emission and its reprocessing in the central engine of a changing-look AGN. The X-ray and UV variability amplitudes are higher than those typically observed in `steady-state' AGN at similar moderate accretion rates; instead, the variability is similar to that of highly accreting AGN. The unusually strong X-ray to UV correlation suggests that the UV-emitting region is directly illuminated by X-ray outbursts. We find evidence that the X-rays are reprocessed by two UV components, with the dominant one at $\sim$3 days and a faint additional reprocessor at near-zero lag. However, we exclude a significant contribution from diffuse broad line region continuum, known to contribute for bona-fide AGN. A near-zero lag is expected for a standard `lamp-post' disk reprocessing model with a driving continuum source near the black hole. That the overall UV response is dominated by the $\sim$3-day lagged component suggests a complicated reprocessing geometry, with most of the UV continuum not produced in a compact disk, as also found in recent studies of NGC 5548 and NGC 4151. Nonetheless, the observed flares display characteristic timescales of $\sim$100 rest-frame days, consistent with the expected thermal timescale in an accretion disk.

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arXiv2022

Demographics of z ~ 6 Quasars in the Black Hole Mass-Luminosity Plane

We study the demographics of z ~ 6 broad-line quasars in the black hole (BH) mass-luminosity plane using a sample of more than 100 quasars at 5.7 < z < 6.5. These quasars have well quantified selection functions and nearly one third of them also have virial BH masses estimated from near-IR spectroscopy. We use forward modeling of parameterized intrinsic distributions of BH masses and Eddington ratios, and account for the sample flux limits and measurement uncertainties of the BH masses and luminosities. We find significant differences between the intrinsic and observed distributions of the quantities due to measurement uncertainties and sample flux limits. There is also marginal evidence that the virial BH masses are susceptible to a positive luminosity-dependent bias (BH mass is overestimated when luminosity is above the average), and that the mean Eddington ratio increases with BH mass. Our models provide reliable constraints on the z ~ 6 black hole mass function at M_BH > 10^8.5 M_Sun, with a median 1-sigma uncertainty of ~0.5 dex in abundance. The intrinsic Eddington ratio distribution of M_BH > 10^8.5 M_Sun quasars can be approximated by a mass-dependent Schechter model, with a broad peak around log(L_bol/L_Edd}) ~ -0.9. We also find that, at 4.5 < z < 6, the number densities of more massive BHs tend to decline more rapidly with increasing redshift, contrary to the trend at 2.5 < z < 4.5 reported previously.

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