Clumpy Torus Models Research Articles

AGNfitter-rx : Modeling the radio-to-X-ray spectral energy distributions of AGNs

We present new advancements in the modeling of the spectral energy distributions (SEDs) of active galaxies by introducing the radio-to-X-ray fitting capabilities of the publicly available Bayesian code AGNfitter . The new code release, called AGNfitter-rx models the broad-band photometry covering the radio, infrared (IR), optical, ultraviolet (UV), and X-ray bands consistently using a combination of theoretical and semi-empirical models of the active galactic nucleus (AGN) and host-galaxy emission. This framework enables the detailed characterization of four physical components of the active nuclei, namely the accretion disk, the hot dusty torus, the relativistic jets and core radio emission, and the hot corona, and can be used to model three components within the host galaxy: stellar populations, cold dust, and the radio emission from the star-forming regions. Applying AGNfitter-rx to a diverse sample of 36 AGN SEDs at $z 0.7$ from the AGN SED ATLAS, we investigated and compared the performance of state-of-the-art torus and accretion disk emission models in terms of fit quality and inferred physical parameters. We find that clumpy torus models that include polar winds and semi-empirical accretion disk templates including emission-line features significantly increase the fit quality in 67<!PCT!> of the sources by reducing by $2 fit residuals in the $1.5-5 1mm m$ and $0.7 1mm m$ regimes. We demonstrate that, by applying AGNfitter-rx to photometric data, we are able to estimate the inclination and opening angles of the torus, consistent with spectroscopic classifications within the AGN unified model, as well as black hole masses congruent with virial estimates based on Halpha . We investigate wavelength-dependent AGN fractions across the spectrum for Type 1 and Type 2 AGNs, finding dominant AGN fractions in radio, mid-infrared, and X-ray bands, which are in agreement with the findings from empirical methods for AGN selection. The wavelength coverage and the flexibility for the inclusion of state-of-the-art theoretical models make AGNfitter-rx a unique tool for the further development of SED modeling for AGNs in present and future radio-to-X-ray galaxy surveys.

O iv]- and [Ne v]-weak Active Galactic Nuclei Hidden by Compton-thick Material in Late Mergers

We study “buried” active galactic nuclei (AGNs) almost fully covered by circumnuclear material in ultra/luminous infrared galaxies (U/LIRGs), which show weak ionized lines from narrow-line regions. Employing an indicator of a [O iv] 25.89 or [Ne v] 14.32 μm line to 12 μm AGN luminosity ratio, we find 17 buried AGN candidates that are [O iv]-weak (L [O IV]/L 12,AGN ≤ −3.0) or [Ne v]-weak (L [Ne V]/L 12,AGN ≤ −3.4) among 30 AGNs in local U/LIRGs. For the [O iv]-weak AGNs, we estimate their covering fractions of Compton-thick (CT; N H ≥ 1024 cm−2) material with an X-ray clumpy torus model to be fCT(spec)=0.55±0.19 on average. This value is consistent with the fraction of CT AGNs ( fCT(stat)=53%±12% ) among the [O iv]-weak AGNs in U/LIRGs and much larger than that in Swift/Burst Alert Telescope (BAT) AGNs (23% ± 6%). The fraction of [O iv]-weak AGNs increases from 27−10+13% (early) to 66−12+10% (late mergers). Similar results are obtained with the [Ne v] line. The [O iv]- or [Ne v]-weak AGNs in late mergers show larger N H and Eddington ratios (λ Edd) than those of the Swift/BAT AGNs, and the largest N H is ≳1025 cm−2 at logλEdd∼−1 , close to the effective Eddington limit for CT material. These suggest that (1) the circumnuclear material in buried AGNs is regulated by the radiation force from high-λ Edd AGNs on the CT obscurers, and (2) their dense material with large fCT(spec) (∼0.5 ± 0.1) in U/LIRGs is a likely cause of a unique structure of buried AGNs, whose amount of material may be maintained through merger-induced supply from their host galaxies.

The Galaxy Activity, Torus, and Outflow Survey (GATOS)

We use JWST/MIRI MRS spectroscopy of a sample of six local obscured type 1.9/2 active galactic nuclei (AGN) to compare their nuclear mid-IR absorption bands with the level of nuclear obscuration traced by X-rays. This study is the first to use subarcsecond angular resolution data of local obscured AGN to investigate the nuclear mid-IR absorption bands with a wide wavelength coverage (4.9–28.1 μm). All the nuclei show the 9.7 μm silicate band in absorption. We compare the strength of the 9.7 and 18 μm silicate features with torus model predictions. The observed silicate features are generally well explained by clumpy and smooth torus models. We report the detection of the 6 μm dirty water ice band (i.e., a mix of water and other molecules such as CO and CO2) at subarcsecond scales (∼0.26″ at 6 μm; inner ∼50 pc) in a sample of local AGN with different levels of nuclear obscuration in the range log NHX-Ray (cm−2)∼22 − 25. We find good correlation between the 6 μm water ice optical depths and NHX-Ray. This result indicates that the water ice absorption might be a reliable tracer of the nuclear intrinsic obscuration in AGN. The weak water ice absorption in less obscured AGN (log NHX-ray (cm−2)≲23.0 cm−2) might be related to the hotter dust temperature (> TsubH2O ∼ 110 K) expected to be reached in the outer layers of the torus due to their more inhomogeneous medium. Our results suggest it might be necessary to include the molecular content, such as H2O, aliphatic hydrocarbons (CH−), and more complex polycyclic aromatic hydrocarbon (PAH) molecules, in torus models to better constrain key parameters such as the torus covering factor (i.e., nuclear obscuration).

Modeling the Spectral Energy Distribution of the Active Galactic Nucleus inside NGC 4395

We study the broadband spectral energy distribution (SED) of the prototypical low-mass active galactic nucleus (AGN) in NGC 4395. We jointly model the optical through mid-IR SED with a combination of galaxy and AGN light, and find that on arcsecond scales the AGN dominates at most wavelengths. However, there is still some ambiguity about emission from the galaxy, owing partially to the strong short-term variability of the black hole. We investigate the use of smooth- and clumpy-torus models in order to disentangle the nuclear IR emission, as well as exploring the use of poloidal wind emission to account for the blue spectral slope observed in the near-IR. Even when simultaneously fitting the full optical–IR spectral range, we find that degeneracies still remain in the best-fit models. We conclude that high-spatial-resolution and wider-wavelength coverage with the JWST is needed to understand the mid-IR emission in this complex, highly variable object, which is the best nearby example to provide a blueprint to finding other low-mass AGNs via their mid-IR emission in the future.

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.

Broad-band X-ray spectral study of nuclear structure in local obscured radio galaxies

ABSTRACT Radio galaxies are a key population to understand the importance of relativistic jets in active galactic nucleus (AGN) feedback. We present the results of a systematic, broad-band X-ray spectral analysis of hard X-ray selected radio galaxies to investigate their nuclear structures. In this study, we focus on the seven most radio-loud, X-ray obscured narrow-line radio galaxies in the Swift/BAT 70 month AGN catalogue. The spectra from 0.5 keV up to 66 keV obtained with Suzaku and NuSTAR of six objects are newly analysed here by utilizing the X-ray clumpy torus model (xclumpy), whereas we refer to the literature for the results of Centaurus A. We find that these radio galaxies have similar torus covering fractions compared with radio-quiet AGNs at the same Eddington ratios (−3 < log λEdd < −1). This result implies that (1) the torus structure is not an important factor that determines the presence of jets and (2) AGN jets have physically little effect on the torus.

X-ray radiative transfer in full 3D with SKIRT

Context. Models of active galactic nuclei (AGN) suggest that their circumnuclear media are complex with clumps and filaments, while recent observations hint towards polar extended structures of gas and dust, as opposed to the classical torus paradigm. The X-ray band could form an interesting observational window to study these circumnuclear media in great detail. Aims. We want to extend the radiative transfer code SKIRT with the X-ray processes that govern the broad-band X-ray spectra of obscured AGN, to study the structure of AGN circumnuclear media in full 3D, based on their reflected X-ray emission. Methods. We extended the SKIRT code with Compton scattering on free electrons, photo-absorption and fluorescence by cold atomic gas, scattering on bound electrons, and extinction by dust. This includes a novel treatment of extreme-forward scattering by dust, and a detailed description of anomalous Rayleigh scattering. To verify our X-ray implementation, we performed the first dedicated benchmark of X-ray torus models, comparing five X-ray radiative transfer codes. Results. The resulting radiative transfer code covers the X-ray to millimetre wavelength range self-consistently, has all the features of the established SKIRT framework, is publicly available, and is fully optimised to operate in arbitrary 3D geometries. In the X-ray regime, we find an excellent agreement with the simulation results of the MYTORUS and REFLEX codes, which validates our X-ray implementation. We find some discrepancies with other codes, which illustrates the complexity of X-ray radiative transfer and motivates the need for a robust framework that can handle non-linear 3D radiative transfer effects. We illustrate the 3D nature of the code by producing synthetic X-ray images and spectra of clumpy torus models. Conclusions. SKIRT forms a powerful new tool to model circumnuclear media in full 3D, and make predictions for the X-ray band in addition to the dust-dominated infrared-to-UV wavelength range. The new X-ray functionalities of the SKIRT code allow for uncomplicated access to a broad suite of 3D X-ray models for AGN that can easily be tested and modified. This will be particularly useful with the advent of X-ray microcalorimeter observations in the near future.

Torus and polar dust dependence on active galactic nucleus properties

We present a statistical analysis of the properties of the obscuring material around active galactic nuclei (AGN). This study represents the first of its kind for an ultra-hard X-ray (14–195 keV; Swift/BAT), volume-limited (DL < 40 Mpc) sample of 24 Seyfert (Sy) galaxies (BCS40 sample) using high angular resolution infrared data and various torus models: smooth, clumpy, and two-phase torus models and clumpy disc+wind models. We find that torus models (i.e. without including the polar dusty wind component) and disc+wind models provide the best fits for a comparable number of galaxies, 8 out of 24 (33.3%) and 9 out of 24 (37.5%), respectively. We find that the best-fit models depend on the hydrogen column density (NHX−ray), which is related to the X-ray (unobscured or obscured) and optical (Sy1/Sy2) classification. In particular, smooth, clumpy, and two-phase torus models are best at reproducing the infrared (IR) emission of AGN with relatively high hydrogen column density (median value of log (NHX−ray cm−2) = 23.5 ± 0.8; i.e. Sy2). However, clumpy disc+wind models provide the best fits to the nuclear IR spectral energy distributions (SEDs) of Sy1/1.8/1.9 (median value of log (NHX−ray cm−2) = 21.0 ± 1.0) – specifically, in the near-infrared (NIR) range. The success of the disc+wind models in fitting the NIR emission of Sy1 galaxies is due to the combination of adding large graphite grains to the dust composition and self-obscuration effects caused by the wind at intermediate inclinations. In general, we find that the Seyfert galaxies having unfavourable (favourable) conditions, namely, nuclear hydrogen column density and Eddington ratio, for launching IR dusty polar outflows are best-fitted with smooth, clumpy, and two-phase torus (disc+wind) models, confirming the predictions from simulations. Therefore, our results indicate that the nature of the inner dusty structure in AGN depends on the intrinsic AGN properties.

On Planet Formation around Supermassive Black Holes and Grain Disruption Barriers by Radiative Torques

It has recently been suggested that planets can form by dust coagulation in the tori of active galactic nuclei (AGN) with low luminosities of L bol ≲ 1042 erg s−1, constituting a new class of exoplanets orbiting supermassive black holes called blanets. However, large dust grains in the AGN torus may be rotationally disrupted by the radiative torque disruption (RATD) mechanism due to AGN radiation feedback, which would prevent blanet formation. To test this scenario, we adopt a simple smooth and a clumpy dust/gas distribution inside the torus region to study the effect of RATD on the evolution of composite dust grains in the midplane of the torus. We found that grain growth and then blanet formation are possible in the smooth torus model. However, in the clumpy torus model, grain growth will be strongly constrained by RATD, assuming the gas density distribution as adopted by Wada et al. We also found that icy grain mantles inside clumps are quickly detached from the grain cores by rotational desorption, reducing the sticking coefficient between icy grains and the coagulation efficiency. The grain rotational disruption and ice desorption occur on timescales much shorter than the growth time up to a factor of ∼104, which are the new barriers that grain growth must overcome to form blanets. Further studies with more realistic AGN models are required to constrain better the effect of RATD on grain growth and blanet formation hypothesis around low-luminosity AGN.

The Complex Infrared Dust Continuum Emission of NGC 1068: Ground-based N- and Q-band Spectroscopy and New Radiative Transfer Models

Abstract Thanks to ground-based infrared and submillimeter observations the study of the dusty torus of nearby active galactic nuclei has greatly advanced in the last years. With the aim of further investigating the nuclear mid-infrared emission of the archetypal Seyfert 2 galaxy NGC 1068, here we present a fitting to the N- and Q-band Michelle/Gemini spectra. We initially test several available spectral energy distribution (SED) libraries, including smooth, clumpy and two-phase torus models, and a clumpy disk+wind model. We find that the spectra of NGC 1068 cannot be reproduced with any of these models. Although, the smooth torus models describe the spectra of NGC 1068 if we allow variation of some model parameters among the two spectral bands. Motivated by this result, we produced new SEDs using the radiative transfer code SKIRT. We use two concentric tori that allow us to test a more complex geometry. We test different values for the inner and outer radii, half-opening angle, radial, and polar exponent of the power-law density profile, opacity, and viewing angle. Furthermore, we also test the dust grains’ size and different optical and calorimetric properties of silicate grains. The best-fitting model consists of two concentric components with outer radii of 1.8 and 28 pc, respectively. We find that the size and the optical and calorimetric properties of graphite and silicate grains in the dust structure are key to reproducing the spectra of NGC 1068. A maximum grain size of 1 μm leads to a significant improvement in the fit. We conclude that the dust in NGC 1068 reaches different scales, where the highest contribution to the mid-infrared is given by a central and compact component. A less dense and extended component is present, which can be either part of the same torus (conforming a flared disk) or can represent the emission of a polar dust component, as already suggested from interferometric observations.

Hypercubes of AGN Tori (HYPERCAT). II. Resolving the Torus with Extremely Large Telescopes

Abstract Recent infrared interferometric observations revealed sub-parsec scale dust distributions around active galactic nuclei (AGNs). Using images of Clumpy torus models and NGC 1068 as an example, we demonstrate that the near- and mid-infrared nuclear emission of some nearby AGNs will be resolvable in direct imaging with the next generation of 30 m telescopes, potentially breaking degeneracies from previous studies that used integrated spectral energy distributions of unresolved AGN tori. To that effect we model wavelength-dependent point spread functions from the pupil images of various telescopes: James Webb Space Telescope, Keck, Giant Magellan Telescope, Thirty Meter Telescope, and Extremely Large Telescope. We take into account detector pixel scales and noise, and apply deconvolution techniques for image recovery. We also model 2D maps of the 10 μm silicate feature strength, S 10, of NGC 1068 and compare with observations. When the torus is resolved, we find S 10 variations across the image. However, to reproduce the S 10 measurements of an unresolved torus a dusty screen of A V > 9 mag is required. We also fit the first resolved image of the K-band emission in NGC 1068 recently published by the GRAVITY Collaboration, deriving likely model parameters of the underlying dust distribution. We find that both (1) an elongated structure suggestive of a highly inclined emission ring, and (2) a geometrically thin but optically thick flared disk where the emission arises from a narrow strip of hot cloud surface layers on the far inner side of the torus funnel, can explain the observations.

Comprehensive Broadband X-Ray and Multiwavelength Study of Active Galactic Nuclei in 57 Local Luminous and Ultraluminous Infrared Galaxies Observed with NuSTAR and/or Swift/BAT

Abstract We perform a systematic X-ray spectroscopic analysis of 57 local luminous and ultraluminous infrared galaxy systems (containing 84 individual galaxies) observed with the Nuclear Spectroscopic Telescope Array and/or Swift/BAT. Combining soft X-ray data obtained with Chandra, XMM-Newton, Suzaku, and/or Swift/XRT, we identify 40 hard (>10 keV) X-ray–detected active galactic nuclei (AGNs) and constrain their torus parameters with the X-ray clumpy torus model XCLUMPY. Among the AGNs at z < 0.03, for which sample biases are minimized, the fraction of Compton-thick (N H ≥ 1024 cm−2) AGNs reaches 64 − 15 + 14 % (6/9 sources) in late mergers, while it is 24 − 10 + 12 % (3/14 sources) in early mergers, consistent with the tendency reported by Ricci et al. We find that the bolometric AGN luminosities derived from the infrared data increase but the X-ray to bolometric luminosity ratios decrease with merger stage. The X-ray-weak AGNs in late mergers ubiquitously show massive outflows at subparsec to kiloparsec scales. Among them, the most luminous AGNs (L bol,AGN ∼ 1046 erg s−1) have relatively small column densities of ≲1023 cm−2 and almost super-Eddington ratios (λ Edd ∼ 1.0). Their torus covering factors (C T (22) ∼ 0.6) are larger than those of Swift/BAT-selected AGNs with similarly high Eddington ratios. These results suggest a scenario where, in the final stage of mergers, multiphase strong outflows are produced due to chaotic quasi-spherical inflows, and the AGN becomes extremely X-ray weak and deeply buried due to obscuration by inflowing and/or outflowing material.

Physically motivated X-ray obscurer models

Context. The nuclear obscurer of active galactic nuclei (AGN) is poorly understood in terms of its origin, geometry, and dynamics. Aims. We investigate whether physically motivated geometries emerging from hydro-radiative simulations can be differentiated with X-ray reflection spectroscopy. Methods. For two new geometries, the radiative fountain model and a warped disk, we release spectral models produced with the ray tracing code XARS. We contrast these models with spectra of three nearby AGN taken by NuSTAR and Swift/BAT. Results. Along heavily obscured sightlines, the models present different 4−20 keV continuum spectra. These can be differentiated by current observations. Spectral fits of the Circinus Galaxy favour the warped disk model over the radiative fountain, and clumpy or smooth torus models. Conclusions. The necessary reflector (NH ≥ 1025 cm2) suggests a hidden population of heavily Compton-thick AGN amongst local galaxies. X-ray reflection spectroscopy is a promising pathway to understand the nuclear obscurer in AGN.

The Dusty Heart of NGC 4151 Revealed by λ ∼ 1–40 μm Reverberation Mapping and Variability: A Challenge to Current Clumpy Torus Models

Abstract We probe the dusty environment of the archetypical Type 1 active galactic nucleus (AGN) in NGC 4151 with comprehensive IR reverberation mapping over several decades, in the J (∼1.22 μm), H (∼1.63 μm), K (∼2.19 μm), L (∼3.45 μm), and N bands (∼10.6 μm), plus multiple measurements at 20–40 μm. At 1–4 μm, the hot dust reverberation signals come from two distinct dust populations at separate radii (∼0.033 pc and ∼0.076 pc), with temperatures of ∼1500–2500 K and ∼900–1000 K, consistent with the expected properties of sublimating graphite and silicate dust grains. The domination of the torus infrared output by carbon and silicate grains near their sublimation temperatures and radii may account for the general similarity of AGN near-IR spectral energy distributions. The torus inner edge defined by the hottest dust remains at roughly the same radius independent of the AGN optical luminosity over ∼25 yr. The emission by hot dust warmed directly by the optical/UV AGN output has increased gradually by ∼4% yr−1, indicating a possibly growing torus. A third dust component at ∼700 K does not seem to participate directly in the IR reverberation behavior, and its emission may originate deep in the circumnuclear torus. We find a reverberation signal at ∼10 μm with an inferred radius for the warm dust of ∼2.2–3.1 pc. The lack of variability at 20–40 μm indicates that the far-IR emission comes from even more extended regions. The torus properties revealed by dust reverberation analysis are inconsistent with predictions from pure clumpy torus models. Instead, the longer-wavelength emission possibly originates in a flared torus or the polar wind.

How Does the Polar Dust Affect the Correlation between Dust Covering Factor and Eddington Ratio in Type 1 Quasars Selected from the Sloan Digital Sky Survey Data Release 16?

Abstract We revisit the dependence of the covering factor (CF) of dust torus on physical properties of active galactic nuclei (AGNs) by taking into account an AGN polar dust emission. The CF is converted from a ratio of infrared (IR) luminosity contributed from AGN dust torus ( ) and AGN bolometric luminosity (L bol), by assuming a nonlinear relation between luminosity ratio and intrinsic CF. We select 37,181 type 1 quasars at z < 0.7 from the Sloan Digital Sky Survey Data Release 16 quasar catalog. Their L bol, black hole mass (M BH), and Eddington ratio (λ Edd) are derived by spectral fitting with QSFit. We conduct spectral energy distribution decomposition by using X-CIGALE with a clumpy torus and polar dust model to estimate without being affected by the contribution of stellar and AGN polar dust to IR emission. For 5752 quasars whose physical quantities are securely determined, we perform a correlation analysis on CF and (i) L bol, (ii) M BH, and (iii) λ Edd. As a result, anticorrelations for CF–L bol, CF–M BH, and CF–λ Edd are confirmed. We find that incorporating the AGN polar dust emission makes those anticorrelations stronger compared to those without considering it. This indicates that polar dust wind probably driven by AGN radiative pressure is one of the key components to regulate obscuring material of AGNs.

X-Ray Constraint on the Location of the AGN Torus in the Circinus Galaxy

Abstract The location of the obscuring “torus” in an active galactic nucleus (AGN) is still an unresolved issue. The line widths of X-ray fluorescence lines originating from the torus, particularly Fe Kα, carry key information on the radii of line-emitting regions. Utilizing XCLUMPY, an X-ray clumpy torus model, we develop a realistic model of emission line profiles from an AGN torus where we take into account line broadening due to the Keplerian motion around the black hole. Then, we apply the updated model to the best available broadband spectra (3–100 keV) of the Circinus galaxy observed with Suzaku, XMM-Newton, Nuclear Spectroscopic Telescope Array, and Chandra, including 0.62 Ms Chandra/HETG data. We confirm that the torus is Compton-thick (hydrogen column density along the equatorial plane is ), geometrically thin (torus angular width ), viewed edge-on (inclination ), and has supersolar abundance ( times solar). Simultaneously analyzing the Chandra/HETG first-, second-, and third-order spectra with consideration of the spatial extent of the Fe Kα line-emitting region, we constrain the inner radius of the torus to be times the gravitational radius, or for a black hole mass of (1.7 ± 0.3) × 106 M ⊙. This is about three times smaller than that estimated from the dust sublimation radius, suggesting that the inner side of the dusty region of the torus is composed of dust-free gas.

Black Hole and Galaxy Coevolution in Moderately Luminous Active Galactic Nuclei at z ∼ 1.4 in SXDF

Abstract We investigate the relation of black hole mass versus host stellar mass and that of mass accretion rate versus star formation rate (SFR) in moderately luminous ( ), X-ray selected broad-line active galactic nuclei (AGNs) at z = 1.18–1.68 in the Subaru/XMM-Newton Deep Field. The far-infrared to far-ultraviolet spectral energy distributions of 85 AGNs are reproduced with the latest version of Code Investigating GALaxy Emission (CIGALE), where the AGN clumpy torus model SKIRTOR is implemented. Most of their hosts are confirmed to be main-sequence star-forming galaxies. We find that the mean ratio of the black hole mass (M BH) to the total stellar mass (M stellar) is , which is similar to the local black hole–to–bulge mass ratio. This suggests that if the host galaxies of these moderately luminous AGNs at z ∼ 1.4 are dominated by bulges, they already established the local black hole mass–bulge mass relation; if they are disk dominant, their black holes are overmassive relative to the bulges. The AGN bolometric luminosities and SFR show a good correlation with ratios higher than that expected from the local black hole-to-bulge mass relation, suggesting that these AGNs are in a SMBH-growth dominant phase.

Systematic Study of AGN Clumpy Tori with Broadband X-Ray Spectroscopy: Updated Unified Picture of AGN Structure

Abstract We present the results of a systematic, broadband X-ray spectral analysis of nearby active galactic nuclei (AGNs) with the X-ray clumpy torus model (XCLUMPY). By adding 16 AGNs newly analyzed in this paper, we study a total of 28 AGNs, including unabsorbed and absorbed AGNs taken from Ichikawa et al. and García-Bernete et al. This is the largest sample whose X-ray and infrared spectra are analyzed by the clumpy torus models XCLUMPY and CLUMPY, respectively. The relation between the Eddington ratio and the torus covering factor determined from the X-ray torus parameters of each object follows the trend found by Ricci et al. based on a statistical analysis. We confirm the results by Tanimoto et al. that (1) the torus angular widths determined by the infrared data are larger than those by the X-ray data and (2) the ratios of hydrogen column density to V-band extinction (N H/A V ) along the line of sight in obscured AGNs are similar to the Galactic value, on average. Unobscured AGNs show apparently smaller line-of-sight N H/A V ratios than the Galactic one. Our findings can be well explained by an updated unified picture of AGN structure including a dusty torus, dusty polar outflows, and dust-free gas, where the inclination determines the X-ray and optical classifications and observed torus properties in the X-ray and infrared bands.

Searching for Nuclear Obscuration in the Infrared Spectra of Nearby FR I Radio Galaxies

Abstract How do active galactic nuclei with low optical luminosities produce powerful radio emission? Recent studies of active galactic nuclei with moderate radio and low optical luminosities (Fanaroff & Riley class I, FR I) searching for broad nuclear emission lines in polarized light, as predicted by some active galactic nucleus unification models, have found heterogeneous results. These models typically consist of a central engine surrounded by a torus of discrete dusty clouds. These clouds would absorb and scatter optical emission, blocking broad nuclear emission lines, and reradiate in mid-infrared. Some scattered broad-line emission may be observable, depending on geometry, which would be polarized. We present a wide-band infrared spectroscopic analysis of 10 nearby FR I radio galaxies to determine whether there is significant emission from a dusty obscuring structure. We used Markov Chain Monte Carlo algorithms to decompose Spitzer/IRS spectra of our sample. We constrained the wide-band behavior of our models with photometry from the Two Micron All Sky Survey, Spitzer/IRAC, Spitzer/MIPS, and Herschel/SPIRE. We find that one galaxy is best fit by a clumpy torus and three others show some thermal mid-infrared component. This suggests that in those three there is likely some obscuring dust structure that is inconsistent with our torus models and there must be some source of photons heating the dust. We conclude that 40% of our FR I radio galaxies show evidence of obscuring dusty material, possibly some other form of hidden broad-line nucleus, but only 10% favor the clumpy torus model specifically.

X-ray absorption and 9.7 μm silicate feature as a probe of AGN torus structure

The dusty torus plays a vital role in unifying active galactic nuclei (AGNs). However, the physical structure of the torus remains largely unclear. Here we present a systematical investigation of the torus mid-infrared (MIR) spectroscopic feature, i.e., the 9.7μm silicate line, of 175 AGNs selected from the Swift/BAT Spectroscopic Survey (BASS). Our sample is constructed to ensure that each of the 175 AGNs has Spizter/IRS MIR, optical, and X-ray spectroscopic coverage. Therefore, we can simultaneously measure the silicate strength, optical emission lines, and X-ray properties (e.g., the column density and the intrinsic X-ray luminosity). We show that, consistent with previous works, the silicate strength is weakly correlated with the hydrogen column density (), albeit with large scatters. For X-ray unobscured AGNs, the silicate-strength-derived V-band extinction and the broad-Hα-inferred one are both small; however, for X-ray obscured AGNs, the former is much larger than the latter. In addition, we find that the optical type 1 AGNs with strong X-ray absorption on average show significant silicate absorption, indicating that their X-ray absorption might not be caused by dust-free gas in the broad-line region. Our results suggest that the distribution and structure of the obscuring dusty torus are likely to be very complex. We test our results against the smooth and clumpy torus models and find evidence in favor of the clumpy torus model.