Active Galactic Nuclei Continuum Research Articles

The Spectral Energy Distributions and Bolometric Luminosities of Local AGN: Study of the Complete 12 μm AGN Sample

We measure the bolometric luminosity of a complete and unbiased 12 μm-selected sample of active galactic nuclei (AGN) in the local Universe. For each galaxy, we used a 10-band radio-to-X-ray spectral energy distribution (SED) to isolate the genuine AGN continuum in each band, including subarcsecond measurements where available, and correcting those contaminated by the host galaxy. We derive the median SED of Seyfert type 1 AGN, Seyferts with hidden broad lines (HBLs), Seyferts of type 2, and LINER nuclei in our sample. The median Seyfert 1 SED shows the characteristic blue bump feature in the UV, but nevertheless, the largest contribution to the bolometric luminosity comes from the IR and X-ray continua. The median SEDs of both HBL and type 2 AGN are affected by starlight contamination in the optical/UV. The median SED of HBL AGN is consistent with that of Seyfert 1s, when an extinction of A V ∼ 1.2 mag is applied. The comprehensive SEDs allowed us to measure accurate bolometric luminosities and derive robust bolometric corrections for the different tracers. The 12 μm and K-band nuclear luminosities have good linear correlations with the bolometric luminosity, similar to those in the X-rays. We derive bolometric corrections for either continuum bands (K band, 12 μm, 2–10 keV, and 14–195 keV) or narrow emission lines (mid-IR high-ionization lines of [O iv] and [Ne v] and optical [O iii] 5007 Å) as well as for combinations of IR continuum and line emission. A combination of continuum plus line emission accurately predicts the bolometric luminosity up to quasar luminosities (∼1046 erg s−1).

The Relationships between Active Galactic Nucleus Power and Molecular Gas Mass within 500 pc of the Center of Elliptical Galaxies

The physical quantity that directly controls the feedback of active galactic nuclei (AGNs) in elliptical galaxies remains to be determined. The discovery of molecular gas around the AGNs suggests that the gas is fueling the AGNs. Therefore, we analyze Atacama Large Millimeter/submillimeter Array data for the CO line (J = 1–0, 2–1, 3–2) emission and estimate the mass of molecular gas within 500 pc of the center of 12 noncentral elliptical galaxies (NCEGs) and 10 of the brightest cluster galaxies. We find that the mass (M mol ∼ 105–109 M ☉) is correlated with the jet power of their AGNs, which is represented by Pcav≈4.1×1042(Mmol/107M☉)1.3ergs−1 , although NCEGs alone do not show the correlation. We also find that M mol is correlated with the AGN continuum luminosities at ∼1.4 GHz (L 1.4) and ∼100–300 GHz (L con). Since P cav reflects galactic-scale, long-term AGN activity, while the continuum luminosities reflect local (≲500 pc), short-term AGN activity, our results suggest that AGN activity depends on the amount of gas, regardless of its timescale. On the other hand, we cannot find a clear correlation between the mass of the black holes in the AGNs (M BH) and P cav. This suggests that M mol, rather than M BH, is the main factor controlling AGN activity. We confirm that the origin of the continuum emission from the AGNs at ∼1.4–300 GHz is mostly synchrotron radiation.

The narrow-line region properties of ESO 138-G001 unveiled by SOAR/SIFS observations

ABSTRACT We study in detail the inner ∼600 pc of the Seyfert 2 galaxy ESO 138-G001 by means of the Soar Integral Field Spectrograph attached to the SOAR telescope. This source is known for displaying a very rich coronal line spectrum and a blob of high-excitation emission ∼3 arcsec south-east (SE) of the active galactic nucleus (AGN). The nature of this emission has not been fully understood yet. The excellent spatial and spectral resolution of SIFS allows us to confirm that the bulk of the coronal line forest emission region is very compact, of ∼0.8 arcsec in diameter, centred on the AGN and most likely powered by radiation from the AGN. In addition, evidence of a nuclear outflow, restricted to the inner 1 arcsec centred at the nucleus is found based on the detection of broad components in the most important emission lines. The gas in the inner few tens of parsecs filters out the AGN continuum so that the NLR is basically illuminated by a modified SED. This scenario is confirmed by means of photoionization models that reproduce the most important lines detected in the SIFS field of view. From the modelling, we also found that the black hole mass MBH of the AGN is about 105.50 M⊙, in agreement with previous X-ray observations. The spectrum of the SE blob is dominated by emission lines of low- to mid-ionization, with no hints of coronal lines. Our results show that it represents gas in the ionization cone that is photoionized by the filtered central AGN continuum.

The role of grain size in active galactic nuclei torus dust models

Context. Active galactic nuclei (AGN) are surrounded by dust within the central parsecs. The dusty circumnuclear structures, referred to as the torus, are mainly heated by radiation from the AGN and emitted at infrared wavelengths, producing the emergent dust continuum and silicate features. Fits to the infrared spectra from the nuclear regions of AGN can place constraints on the dust properties, distribution, and geometry by comparison with models. However, none of the currently available models fully describe the observations of AGN currently available. Aims. Among the aspects least explored, here we focus on the role of dust grain size. We offer the community a new spectral energy distribution (SED) library which is based on the two-phase torus model developed before with the inclusion of the grain size as a model parameter, parameterized by the maximum grain size Psize or equivalently the mass-weighted average grain size ⟨P⟩. Methods. We created 691 200 SEDs using the SKIRT code, where the maximum grain size can vary within the range Psize = 0.01 − 10.0 μm (⟨P⟩ = 0.007 − 3.41 μm). We fit this new library and several existing libraries to a sample of 68 nearby and luminous AGN with Spitzer/IRS spectra dominated by AGN-heated dust. Results. We find that the GoMar23 model can adequately reproduce up to ∼85–88% of the spectra. The dust grain size parameter significantly improves the final fit in up to 90% of these spectra. Statistical tests indicate that the grain size is the third most important parameter in the fitting procedure (after the size and half opening angle of the torus). The requirement of a foreground extinction by our model is lower compared to purely clumpy models. We find that ∼41% of our sample requires that the maximum dust grain size is as large as Psize ∼ 10 μm (⟨P⟩∼3.41 μm). Nonetheless, we also remark that disk+wind and clumpy torus models are still required to reproduce the spectra of a nonnegligible fraction of objects, suggesting the need for several dust geometries to explain the infrared continuum of AGN. Conclusions. This work provides tentative evidence for dust grain growth in the proximity of the AGN.

A Catalog of 71 Coronal Line Galaxies in MaNGA: [Ne v] Is an Effective AGN Tracer

Despite the importance of active galactic nuclei (AGNs) in galaxy evolution, accurate AGN identification is often challenging, as common AGN diagnostics can be confused by contributions from star formation and other effects (e.g., Baldwin–Phillips–Terlevich diagrams). However, one promising avenue for identifying AGNs is “coronal emission lines” (“CLs”), which are highly ionized species of gas with ionization potentials ≥100 eV. These CLs may serve as excellent signatures for the strong ionizing continuum of AGNs. To determine if CLs are in fact strong AGN tracers, we assemble and analyze the largest catalog of optical CL galaxies using the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) catalog. We detect CL emission in 71 MaNGA galaxies, out of the 10,010 unique galaxies from the final MaNGA catalog, with ≥5σ confidence. In our sample, we measure [Ne v]λ3347, λ3427, [Fe vii]λ3586, λ3760, λ6086, and [Fe x]λ6374 emission and crossmatch the CL galaxies with a catalog of AGNs that were confirmed with broad-line, X-ray, IR, and radio observations. We find that [Ne v] emission, compared to [Fe vii] and [Fe x] emission, is best at identifying high-luminosity AGNs. Moreover, we find that the CL galaxies with the least dust extinction yield the most iron CL detections. We posit that the bulk of the iron CLs are destroyed by dust grains in the galaxies with the highest [O iii] luminosities in our sample, and that AGNs in the galaxies with low [O iii] luminosities are possibly too weak to be detected using traditional techniques.

An empirical relation to estimate host galaxy stellar light from AGN spectra

ABSTRACT Measurement of black hole mass for low-z (z≤ 0.8) Active Galactic Nuclei (AGNs) is difficult due to the strong contribution from host galaxy stellar light necessitating detailed spectral decomposition to estimate the AGN luminosity. Here, we present an empirical relation to estimate host galaxy stellar luminosity from the optical spectra of AGNs at z ≤ 0.8. The spectral data were selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalogue having a signal-to-noise ratio at 5100 Å (SNR5100) >10 containing 11 415 quasars. The median total luminosity (log (Ltotal/[erg s−1])), stellar luminosity (log (Lstar/[erg s−1])), and AGN continuum luminosity ((log Lcont/[erg s−1])) in our sample are 44.52, 44.06, and 44.30, respectively. We fit the AGN power-law continuum, host galaxy, and iron blend contribution, simultaneously over the entire available spectrum. We found the host galaxy fraction to anticorrelate with continuum luminosity and can be well-represented by a polynomial function, which can be used to correct the stellar light contribution from AGN spectra. We also found anticorrelation between host galaxy fraction and iron strength, Eddington ratio, and redshift. The empirical relation gives comparable results of host-fraction with the image decomposition method.

Broad-line region in NGC 4151 monitored by two decades of reverberation mapping campaigns – I. Evolution of structure and kinematics

ABSTRACT We report the results of long-term reverberation mapping campaigns of the nearby active galactic nuclei (AGNs) NGC 4151, spanning from 1994 to 2022, based on archived observations of the FAST Spectrograph Publicly Archived Programs and our new observations with the 2.3 m telescope at the Wyoming Infrared Observatory. We reduce and calibrate all the spectra in a consistent way, and derive light curves of the broad H β line and 5100 Å continuum. Continuum light curves are also constructed using public archival photometric data to increase sampling cadences. We subtract the host galaxy contamination using Hubble Space Telescope imaging to correct fluxes of the calibrated light curves. Utilizing the long-term archival photometric data, we complete the absolute flux-calibration of the AGN continuum. We find that the H β time delays are correlated with the 5100 Å luminosities as $\tau _{\rm H\beta }\propto L_{5100}^{0.46\pm 0.16}$. This is remarkably consistent with Bentz et al. (2013)’s global size–luminosity relationship of AGNs. Moreover, the data sets for five of the seasons allow us to obtain the velocity-resolved delays of the H β line, showing diverse structures (outflows, inflows, and discs). Combining our results with previous independent measurements, we find the measured dynamics of the H β broad-line region (BLR) are possibly related to the long-term trend of the luminosity. There is also a possible additional ∼1.86 yr time lag between the variation in BLR radius and luminosity. These results suggest that dynamical changes in the BLR may be driven by the effects of radiation pressure.

Active Galactic Nuclei Continuum Reverberation Mapping Based on Zwicky Transient Facility Light Curves

We perform a systematic survey of active galactic nuclei (AGNs) continuum lags using ∼3 days cadence gri-band light curves from the Zwicky Transient Facility. We select a sample of 94 type 1 AGNs at z < 0.8 with significant and consistent inter-band lags based on the interpolated cross-correlation function method and the Bayesian method JAVELIN. Within the framework of the “lamp-post” reprocessing model, our findings are: (1) The continuum emission (CE) sizes inferred from the data are larger than the disk sizes predicted by the standard thin-disk model. (2) For a subset of the sample, the CE size exceeds the theoretical limit of the self-gravity radius (12 lt-days) for geometrically thin disks. (3) The CE size scales with continuum luminosity as R CE ∝ L 0.48±0.04 with a scatter of 0.2 dex, analogous to the well-known radius–luminosity relation of broad Hβ. These findings suggest a significant contribution of diffuse continuum emission from the broad-line region (BLR) to AGN continuum lags. We find that the R CE–L relation can be explained by a photoionization model that assumes ∼23% of the total flux comes from the diffuse BLR emission. In addition, the ratio of the CE size and model-predicted disk size anticorrelates with the continuum luminosity, which is indicative of a potential nondisk BLR lag contribution evolving with the luminosity. Finally, a robust positive correlation between the CE size and black hole mass is detected.

Reddening and the shape of the variable component of the continua of active galactic nuclei from the optical to the far-ultraviolet – I

ABSTRACT We analyse the photometric variability of 4611 active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) Stripe 82. We recover the spectral energy distribution (SED) of the variable flux as a function of wavelength. For rest wavelengths longer than ∼2200 Å, we find that the SED of the variable component of the bluest AGNs is consistent with the Fν ∝ ν+1/3 spectrum predicted for an externally illuminated accretion disc. We confirm there is some residual variable emission corresponding to the ‘small blue bump’ and other broad-line region variability. We interpret steeper optical spectra of the variable component as being due to intrinsic reddening. This is supported by the correlation of the Balmer decrement with the colour excess of the variable component. We find the median internal reddening of SDSS AGNs in Stripe 82 with z &amp;lt; 0.4 to be E(B − V) ≈ 0.10 in agreement with the reddening derived from the Balmer decrement. Individual AGNs in the sample can have E(B − V) &amp;gt; 0.4.

Circumnuclear Medium around the Central AGN in a Cool-core Cluster, Abell 1644-South

We present the circumnuclear multiphase gas properties of the brightest cluster galaxy (BCG) in the center of Abell 1644-South (A1644-S). A1644-S is the main cluster in a merging system, which is well known for X-ray hot gas sloshing in its core. The sharply peaked X-ray profile of A1644-S implies the presence of a strongly cooling gas core. In this study, we analyze ALMA 12CO (1–0) data, JVLA H i data, and KaVA 22 GHz data for the central region of A1644-S to probe the potential origin of the cool gas and its role in (re)powering the central active galactic nucleus (AGN). We find CO clumps distributed in an arc shape along the X-ray gas sloshing, which is suggestive of a connection between the cold gas and the hot intracluster medium (ICM). H i and CN are detected in absorption against the AGN continuum emission. The absorption dip is observed at the systemic velocity of the BCG with an extended, redshifted tail. Based on the spatial and spectral configurations of the H i, CN, and CO gases, it is inferred that cool gas spirals into the core of the BCG, which is then fed to the central AGN. Indeed, our KaVA observation reveals a parsec-scale bipolar jet, implying that this AGN could have been (re)powered quite recently. Combining this, we suggest that some cold gas in A1644-S could have been formed from the cooling of the ICM, triggering the activity of the central AGN in the early development of a cool-core cluster.

The Lick AGN Monitoring Project 2016: Velocity-resolved Hβ Lags in Luminous Seyfert Galaxies

Abstract We carried out spectroscopic monitoring of 21 low-redshift Seyfert 1 galaxies using the Kast double spectrograph on the 3 m Shane telescope at Lick Observatory from 2016 April to 2017 May. Targeting active galactic nuclei (AGNs) with luminosities of λ L λ (5100 Å) ≈ 1044 erg s−1 and predicted Hβ lags of ∼20–30 days or black hole masses of 107–108.5 M ⊙, our campaign probes luminosity-dependent trends in broad-line region (BLR) structure and dynamics as well as to improve calibrations for single-epoch estimates of quasar black hole masses. Here we present the first results from the campaign, including Hβ emission-line light curves, integrated Hβ lag times (8–30 days) measured against V-band continuum light curves, velocity-resolved reverberation lags, line widths of the broad Hβ components, and virial black hole mass estimates (107.1–108.1 M ⊙). Our results add significantly to the number of existing velocity-resolved lag measurements and reveal a diversity of BLR gas kinematics at moderately high AGN luminosities. AGN continuum luminosity appears not to be correlated with the type of kinematics that its BLR gas may exhibit. Follow-up direct modeling of this data set will elucidate the detailed kinematics and provide robust dynamical black hole masses for several objects in this sample.

Properties of the continuum and broad line emission gas in active galactic nuclei with moderate to strong Feii emission

AbstractWe study a sample of 67 active galactic nuclei (AGN) with moderate to strong Feii emission to investigate the relation between the observed AGN continuum and the lines produced by the broad line region (BLR), in particular, Feii. We found that the continuum in the optical/near‐infrared can be described in terms of two components: a power‐law, characterized by the spectral index α, and hot dust emission, represented by a Plank function of temperature T. These two parameters seem not to be related to the strength of Feii emission. In addition to Feii, we study other low‐ionization BLR lines such as Oi and Caii (hereafter CaT). We found that the full‐width at half maximum of these three lines are similar, suggesting that they are produced in the same spatial region of the BLR. We measure the Feii strength in the optical and the near‐infrared region and found that they are strongly correlated. This result evidences the presence of a common excitation mechanism for the Feii emission in the wavelength interval 4000–24000 Å.

Taming the derivative: Diagnostics of the continuum and Hβ emission in a prototypical Population B active galaxy

AbstractWe report preliminary results on the analysis of the continuum and Hβ light curves of the type‐1 active galactic nucleus (AGN) NGC 5548. We notice a clear signature of shallowing in the trend between the Hβ and the continuum luminosities. We attempt the recovery of this observed Hβ emission trend as a response to large continuum flux increase using CLOUDY photoionization simulations. We explore a wide range in the physical parameters space for modeling the Hβ emission from the broad‐line region (BLR) appropriate for this source. We employ a constant density, single‐cloud model approach in this study and successfully recover the observed shallowing of the Hβ emission with respect to rising AGN continuum. With our modeling, we are able to provide the constraints on the local BLR cloud density and recover the BLR distances (from the continuum source) consistent with the Hβ reverberation mapping estimates. We further discuss the implications of the BLR covering factor and their sizes on recovering the observed trend.

Reverberation Mapping Measurements of Black Hole Masses and Broad-line Region Kinematics in Mrk 817 and NGC 7469

Abstract We present the results from a spectroscopic monitoring campaign to obtain reverberation mapping measurements and investigate the broad-line region (BLR) kinematics for active galactic nuclei (AGNs) of Mrk 817 and NGC 7469. This campaign was undertaken with the Lijiang 2.4 m telescope. The median spectroscopic sampling is 2.0 days for Mrk 817 and 1.0 day for NGC 7469. We detect time lags of the broad emission lines, including Hβ, Hγ, He ii, and He i for both AGNs, including Fe ii for Mrk 817 with respect to the varying AGN continuum at 5100 Å. Investigating the relationship between line widths and time lags of the broad emission lines, we find that the BLR dynamics of Mrk 817 and NGC 7469 are consistent with the virial prediction. We estimate the masses of central supermassive black holes (SMBHs) and the accretion rates of both AGNs. Using the data of this campaign, we construct the velocity-resolved lag profiles of the broad Hγ, Hβ, and He i lines for Mrk 817, which show almost the same kinematic signatures in that the time lags in the red wing are slightly larger than the time lags in the blue wing. For NGC 7469, we only clearly construct the velocity-resolved lag profiles of the broad Hγ and Hβ, which show very similar kinematic signatures to the BLR of Mrk 817. These signatures indicate that the BLR of Keplerian motion in both AGNs seemingly has outflowing components during the monitoring period. We discuss the kinematics of the BLR and the measurements, including SMBH mass and accretion rates.

The Diverse Morphologies and Structures of Dwarf Galaxies Hosting Optically Selected Active Massive Black Holes

Abstract We present a study of 41 dwarf galaxies hosting active massive black holes (BHs) using Hubble Space Telescope observations. The host galaxies have stellar masses in the range of M ⋆ ∼ 108.5–109.5 M ⊙ and were selected to host active galactic nuclei (AGNs) based on narrow emission line ratios derived from Sloan Digital Sky Survey spectroscopy. We find a wide range of morphologies in our sample including both regular and irregular dwarf galaxies. We fit the HST images of the regular galaxies using GALFIT and find that the majority are disk-dominated with small pseudobulges, although we do find a handful of bulge-like/elliptical dwarf galaxies. We also find an unresolved source of light in all of the regular galaxies, which may indicate the presence of a nuclear star cluster and/or the detection of AGN continuum. Three of the galaxies in our sample appear to be Magellanic-type dwarf irregulars and two galaxies exhibit clear signatures of interactions/mergers. This work demonstrates the diverse nature of dwarf galaxies hosting optically selected AGNs. It also has implications for constraining the origin of the first BH seeds using the local BH occupation fraction at low masses—we must account for the various types of dwarf galaxies that may host BHs.

The post-Herschel view of intrinsic AGN emission: constructing templates for galaxy and AGN emission at IR wavelengths

ABSTRACT Measuring the star-forming properties of active galactic nucleus (AGN) hosts is key to our understanding of galaxy formation and evolution. However, this topic remains debated, partly due to the difficulties in separating the infrared (i.e. 1–1000 ${\rm \mu m}$) emission into AGN and star-forming components. Taking advantage of archival far-infrared data from Herschel, we present a new set of AGN and galaxy infrared templates and introduce the spectral energy distribution fitting code iragnsep. Both can be used to measure infrared host galaxy properties, free of AGN contamination. To build these, we used a sample of 100 local (z &amp;lt; 0.3), low-to-high luminosity AGNs (i.e. Lbol$\ \sim \ 10^{42-46}$ erg s−1), selected from the 105-month Swift–BAT X-ray survey, which have archival Spitzer–IRS spectra and Herschel photometry. We first built a set of seven galaxy templates using a sample of 55 star-forming galaxies selected via infrared diagnostics. Using these templates, combined with a flexible model for the AGN contribution, we extracted the intrinsic infrared emission of our AGN sample. We further demonstrate that we can reduce the diversity in the intrinsic shapes of AGN spectral energy distributions down to a set of three AGN templates, of which two represent AGN continuum, and one represents silicate emission. Our results indicate that, on average, the contribution of AGNs to the far-infrared (λ ≳ 50 ${\rm \mu m}$) is not as high as suggested by some recent work. We further show that the need for two infrared AGN continuum templates could be related to nuclear obscuration, where one of our templates appears dominated by the emission of the extended polar dust.

The Correlated Response of the Narrow FeKα Emission Line to the Primary Continuum Changes in the Seyfert Galaxy NGC 2992

Abstract The intensely varying Active Galactic nucleus (AGN) NGC 2992, on timescales of days to years, provides us with a unique testbed to study the response of the narrow FeKα emission line to the changes in the primary 2–10 keV AGN continuum. We find a strong correlation between the narrow FeKα line flux and the 2–10 keV flux with a Spearman correlation coefficient s = 0.70 and probability p &lt; 0.001, over a period of ∼20 yr. There is no evidence of such a correlation in &lt;1 yr, but the FeKα flux responds at ∼3 yr timescales, allowing us to put the reprocessor distance scale to 0.3 pc ≤ d ≤ 1 pc, consistent with that of torus reflection. The primary 2–10 keV continuum of NGC 2992 undergoes a high-low-high transition in ∼16 yr (2003–2019). Future long term monitoring will be crucial.

The Sloan Digital Sky Survey Reverberation Mapping Project: Estimating Masses of Black Holes in Quasars with Single-epoch Spectroscopy

Abstract It is well known that reverberation mapping of active galactic nuclei (AGNs) reveals a relationship between AGN luminosity and the size of the broad-line region, and that use of this relationship, combined with the Doppler width of the broad emission line, enables an estimate of the mass of the black hole at the center of the active nucleus based on a single spectrum. An unresolved key issue is the choice of parameter used to characterize the line width, either FWHM or line dispersion (the square root of the second moment of the line profile). We argue here that use of FWHM introduces a bias, stretching the mass scale such that high masses are overestimated and low masses are underestimated. Here we investigate estimation of black hole masses in AGNs based on individual or “single-epoch” observations, with a particular emphasis in comparing mass estimates based on line dispersion and FWHM. We confirm the recent findings that, in addition to luminosity and line width, a third parameter is required to obtain accurate masses, and that parameter seems to be Eddington ratio. We present simplified empirical formulae for estimating black hole masses from the Hβ λ4861 and C iv λ1549 emission lines. While the AGN continuum luminosity at 5100 Å is usually used to predict the Hβ reverberation lag, we show that the luminosity of the Hβ broad component can be used instead without any loss of precision, thus eliminating the difficulty of accurately accounting for the host-galaxy contribution to the observed luminosity.

Time-delay Measurement of Mg ii Broad-line Response for the Highly Accreting Quasar HE 0413-4031: Implications for the Mg ii–based Radius–Luminosity Relation

Abstract We present the monitoring of the active galactic nuclei continuum and Mg ii broad-line emission for the quasar HE 0413-4031 (z = 1.38) based on the six-year monitoring by the South African Large Telescope (SALT). We manage to estimate a time-delay of days in the rest frame of the source using seven different methods: interpolated cross-correlation function, discrete correlation function (DCF), z-transformed DCF, JAVELIN, two estimators of data regularity (Von Neumann, Bartels), and χ 2 method. This time-delay is below the value expected from the standard radius–luminosity relation. However, based on the monochromatic luminosity of the source and the spectral energy distribution modeling, we interpret this departure as the shortening of the time-delay due to the higher accretion rate of the source, with the inferred Eddington ratio of ∼0.4. The Mg ii line luminosity of HE 0413-4031 responds to the continuum variability as , which is consistent with the light-travel distance of the location of Mg ii emission at R out ∼ 1018 cm. Using the data of 10 other quasars, we confirm the radius–luminosity relation for the broad Mg ii line, which was previously determined for the broad Hβ line for lower-redshift sources. In addition, we detect a general departure of higher-accreting quasars from this relation in analogy to the Hβ sample. After the accretion-rate correction of the light-travel distance, the Mg ii–based radius–luminosity relation has a small scatter of only 0.10 dex.

Stratified disc wind models for the AGN broad-line region: ultraviolet, optical, and X-ray properties

ABSTRACT The origin, geometry, and kinematics of the broad-line region (BLR) gas in quasars and active galactic nuclei (AGN) are uncertain. We demonstrate that clumpy biconical disc winds illuminated by an AGN continuum can produce BLR-like spectra. We first use a simple toy model to illustrate that disc winds make quite good BLR candidates, because they are self-shielded flows and can cover a large portion of the ionizing flux-density (ϕH-nH) plane. We then conduct Monte Carlo radiative transfer and photoionization calculations, which fully account for self-shielding and multiple scattering in a non-spherical geometry. The emergent model spectra show broad emission lines with equivalent widths and line ratios comparable to those observed in AGN, provided that the wind has a volume filling factor of fV ≲ 0.1. Similar emission line spectra are produced for a variety of wind geometries (polar or equatorial) and for launch radii that differ by an order of magnitude. The line emission arises almost exclusively from plasma travelling below the escape velocity, implying that ‘failed winds’ are important BLR candidates. The behaviour of a line-emitting wind (and possibly any ‘smooth flow’ BLR model) is similar to that of the locally optimally emitting cloud model originally proposed by Baldwin et al. (1995), except that the gradients in ionization state and temperature are large-scale and continuous, rather than within or between distinct clouds. Our models also produce UV absorption lines and X-ray absorption features, and the stratified ionization structure can partially explain the different classes of broad absorption line quasars.