Clumpy Torus Models Research Articles

Nature of Compton-thick Active Galactic Nuclei in “Nonmerging” Luminous Infrared Galaxies UGC 2608 and NGC 5135 Revealed with Broadband X-Ray Spectroscopy

Abstract We have analyzed the broadband X-ray spectra of active galactic nuclei (AGNs) in two “nonmerging” luminous infrared galaxies (LIRGs), UGC 2608 and NGC 5135, utilizing the data of Nuclear Spectroscopic Telescope Array, Suzaku, XMM-Newton, and Chandra. Applying the X-ray clumpy-torus model (XCLUMPY), we find that both sources have similar spectra characterized by Compton-thick (CT) absorption ( ∼ 5–7 × 1024 cm−2) and small torus angular width (σ < 20°). The intrinsic 2–10 keV luminosities are × 1043 erg s−1 (UGC 2608) and × 1043 erg s−1 (NGC 5135). The [O iv]-to-nuclear-12 μm luminosity ratios are larger than those of typical Seyferts, which are consistent with the torus covering factors ( 0.7) estimated from the torus angular widths and column densities by X-ray spectroscopy. The torus covering factors and Eddington ratios ( ∼ 0.1) follow the relation found by Ricci et al. for local AGNs, implying that their tori become geometrically thin, due to significant radiation pressure of the AGN that blows out some part of the tori. These results indicate that the CT AGNs in these “nonmerger” LIRGs are just a normal AGN population seen edge-on through a large line-of-sight column density. They are in contrast to the buried CT AGNs in late-stage mergers that have large torus covering factors even at large Eddington ratios.

Application of an X-Ray Clumpy Torus Model (XCLUMPY) to 10 Obscured Active Galactic Nuclei Observed with Suzaku and NuSTAR

Abstract We apply XCLUMPY, an X-ray spectral model from a clumpy torus in an active galactic nucleus (AGN), to the broadband X-ray spectra of 10 obscured AGNs observed with both Suzaku and NuSTAR. The infrared spectra of these AGNs were analyzed by Ichikawa et al. with the CLUMPY code. Because XCLUMPY adopts the same clump distribution as that in the CLUMPY, we can directly compare the torus parameters obtained from the X-ray spectra and those from the infrared spectra. The torus angular widths determined from the infrared spectra (σ IR) are systematically larger than those from the X-ray data (σ X); the difference ( ) correlates with the inclination angle determined from the X-ray spectrum. These results can be explained by the contribution from dusty polar outflows to the observed infrared flux, which becomes more significant at higher inclinations (more edge-on views). The ratio of the hydrogen column density to the V-band extinction in the line-of-sight absorber shows a large scatter (≃1 dex) around the Galactic value, suggesting that a significant fraction of AGNs have dust-rich circumnuclear environments.

Modeling the Strongest Silicate Emission Features of Local Type 1 AGNs

Abstract We measure the 10 and 18 μm silicate features in a sample of 67 local (z < 0.1) type 1 active galactic nuclei (AGN) with available Spitzer spectra dominated by nonstellar processes. We find that the 10 μm silicate feature peaks at with a strength (Si p = ln f p (spectrum)/f p (continuum)) of , while the 18 μm one peaks at with a strength of . We select from this sample sources with the strongest 10 μm silicate strength ( , 10 objects). We carry out a detailed modeling of the infrared spectrometer/Spitzer spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al., and among all models, those including outflows and complex dust composition are the best. We note that even in AGN-dominated galaxies, it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.

X-cigale: fitting AGN/galaxy SEDs from X-ray to infrared

ABSTRACT Code Investigating GALaxy Emission (cigale) is a powerful multiwavelength spectral energy distribution (SED) fitting code for extragalactic studies. However, the current version of cigale is not able to fit X-ray data, which often provide unique insights into active galactic nucleus (AGN) intrinsic power. We develop a new X-ray module for cigale, allowing it to fit SEDs from the X-ray to infrared (IR). We also improve the AGN fitting of cigale from UV-to-IR wavelengths. We implement a modern clumpy two-phase torus model, skirtor. To account for moderately extincted type 1 AGNs, we implement polar-dust extinction. We publicly release the source code (named ‘x-cigale’). We test x-cigale with X-ray detected AGNs in SDSS, COSMOS, and AKARI-NEP. The fitting quality (as indicated by reduced χ2) is good in general, indicating that x-cigale is capable of modelling the observed SED from X-ray to IR. We discuss constrainability and degeneracy of model parameters in the fitting of AKARI-NEP, for which excellent mid-IR photometric coverage is available. We also test fitting a sample of AKARI-NEP galaxies for which only X-ray upper limits are available from Chandra observations, and find that the upper limit can effectively constrain the AGN SED contribution for some systems. Finally, using x-cigale, we assess the ability of Athena to constrain the AGN activity in future extragalactic studies.

Exploring the Mid-infrared SEDs of Six AGN Dusty Torus Models. II. The Data

Abstract This is the second in a series of papers devoted to exploring a set of six dusty models of active galactic nuclei (AGN) with available spectral energy distributions. These models are the smooth torus by Fritz et al., the clumpy torus by Nenkova et al., the clumpy torus by Hönig & Kishimoto, the two-phase torus by Siebenmorgen et al., the two-phase torus by Stalevski et al., and the wind model by Hönig & Kishimoto. The first paper explores discrimination among models and the parameter restriction using synthetic spectra. Here we perform spectral fitting of a sample of 110 AGN drawn from the Swift/BAT survey with Spitzer/IRS spectroscopic data. The aim is to explore which is the model that describes better the data and the resulting parameters. The clumpy wind–disk model by Hönig & Kishimoto provides good fits for ∼50% of the sample, and the clumpy torus model by Nenkova et al. is good at describing ∼30% of the objects. The wind–disk model by Hönig & Kishimoto is better for reproducing the mid-infrared spectra of type 1 Seyferts (with 60% of the type 1 Seyferts well reproduced by this model compared to the 10% well represented by the clumpy torus model by Nenkova et al.), while type 2 Seyferts are equally fitted by both models (roughly 40% of the type 2 Seyferts). Large residuals are found irrespective of the model used, indicating that the AGN dust continuum emission is more complex than predicted by the models or that the parameter space is not well sampled. We found that all the resulting parameters for our AGN sample are roughly constrained to 10%–20% of the parameter space. Contrary to what is generally assumed, the derived outer radius of the torus is smaller (reaching up to a factor of ∼5 smaller for 10 pc tori) for the smooth torus by Fritz et al. and the two-phase torus by Stalevski et al. than the one derived from the clumpy torus by Nenkova et al. Covering factors and line-of-sight viewing angles strongly depend on the model used. The total dust mass is the most robust derived quantity, giving equivalent results for four of these models.

Torus Constraints in ANEPD-CXO245: A Compton-thick AGN with Double-peaked Narrow Lines

Abstract We report on the torus constraints of the Compton-thick active galactic nucleus (AGN) with double-peaked optical narrow-line region emission lines, ANEPD-CXO245, at z = 0.449 in the AKARI NEP Deep Field. The unique infrared data on this field, including those from the nine-band photometry over 2–24 μm with the AKARI Infrared Camera, and the X-ray spectrum from Chandra allow us to constrain torus parameters such as the torus optical depth, X-ray absorbing column, torus angular width (σ), and viewing angle (i). We analyze the X-ray spectrum as well as the UV–optical–infrared spectral energy distribution (UOI-SED) with clumpy torus models in X-ray (XCLUMPY) and infrared (CLUMPY), respectively. From our current data, the constraints on σ–i from both X-rays and UOI show that the line of sight crosses the torus as expected for a type 2 AGN. We obtain a small X-ray scattering fraction (<0.1%), which suggests narrow torus openings, giving preference to the bipolar outflow picture of the double-peaked profile. Comparing the optical depth of the torus from the UOI-SED and the absorbing column density N H from the X-ray spectrum, we find that the gas-to-dust ratio is ≳4 times larger than the Galactic value.

Application of Clumpy Torus Model to Broadband X-Ray Spectra of Two Seyfert 1 Galaxies: IC 4329A and NGC 7469

Abstract We apply a new X-ray clumpy torus model, XCLUMPY, in which the clump distribution is assumed to be the same as that in the infrared clumpy torus model (CLUMPY) by Nenkova et al., to the broadband X-ray spectra of type-1 active galactic nuclei (AGNs) for the first time. We analyze the archival data of IC 4329A and NGC 7469 observed with NuSTAR/Suzaku and NuSTAR/XMM-Newton, respectively, whose infrared spectra were studied with CLUMPY by Ichikawa et al. and optical extinctions (A V) of the tori were estimated. We consider two models, invoking (Model 1) a relativistic reflection component from the accretion disk and (Model 2) a partial absorber. Assuming that the narrow Fe Kα emission line at 6.4 keV originates from the torus, we separate the contribution of the torus reflection components in the total spectra. Our models yield equatorial hydrogen column densities of the tori to be (0.53–1.43) × 1023 cm−2 and (0.84–1.43) × 1024 cm−2, for IC 4329A and NGC 7469, respectively. We find that the N H/A V ratios in the tori are by factors of 25–68 (IC 4329A) and 2.4–3.9 (NGC 7469) smaller than that in the Galactic interstellar medium (ISM). These results suggest that a non-negligible fraction of AGNs are “dust-rich” compared with the Galactic ISM, as opposite to the general trend previously reported in many obscured AGNs.

Torus model properties of an ultra-hard X-ray selected sample of Seyfert galaxies

We characterize for the first time the torus properties of an ultra-hard X-ray (14-195 keV) volume-limited (DL<40 Mpc) sample of 24 Seyfert (Sy) galaxies (BCS40 sample). The sample was selected from the Swift/BAT nine month catalog. We use high angular resolution nuclear infrared (IR) photometry and N-band spectroscopy, the CLUMPY torus models and a Bayesian tool to characterize the properties of the nuclear dust. In the case of the Sy1s we estimate the accretion disk contribution to the subarcsecond resolution nuclear IR SEDs (~0.4'') which is, on average, 46+-28, 23+-13 and 11+-5% in the J-, H- and K-bands, respectively. This indicates that the accretion disk templates that assume a steep fall for longer wavelengths than 1 micron might underestimate its contribution to the near-IR emission. Using both optical (broad vs narrow lines) and X-ray (unabsorbed vs absorbed) classifications, we compare the global posterior distribution of the torus model parameters. We confirm that Sy2s have larger values of the torus covering factor (CT~0.95) than Sy1s (CT~0.65) in our volume-limited Seyfert sample. These findings are independent of whether we use an optical or X-ray classification. We find that the torus covering factor remains essentially constant within the errors in our luminosity range and there is no clear dependence with the Eddington ratio. Finally, we find tentative evidence that even an ultra hard X-ray selection is missing a significant fraction of highly absorbed type 2 sources with very high covering factor tori.

SOFIA/FORCAST resolves 30–40 μm extended dust emission in nearby active galactic nuclei

We present arcsecond-scale observations of the active galactic nuclei (AGNs) of seven nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the 31.5 and 37.1 um filters of the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We isolate unresolved emission from the torus and find extended diffuse emission in six 37.1 um residual images in our sample. Using Spitzer/IRS spectra, we determine the dominant mid-infrared (MIR) extended emission source and attribute it to dust in the narrow line region (NLR) or star formation. We compare the optical NLR and radio jet axes to the extended 37.1 um emission and find coincident axes for three sources. For those AGNs with extended emission coincident with the optical axis, we find that spatial scales of the residual images are consistent with 0.1 - 1 kpc scale distances to which dust can be heated by the AGN. Using previously published subarcsecond 1 - 20 um imaging and spectroscopic data along with our new observations, we construct broadband spectral energy distributions (SEDs) of the AGNs at wavelengths 1 - 40 um. We find that three AGNs in our sample tentatively show a turnover in the SED between 30 - 40 um. Using results from Clumpy torus models and the Bayesian inference tool BayesClumpy, we find that the posterior outputs for AGNs with MIR turnover revealed by SOFIA/FORCAST have smaller uncertainties than AGNs that do not show a turnover.

The hyperluminous Compton-thick z ∼ 2 quasar nucleus of the hot DOG W1835+4355 observed by NuSTAR

We present a 155 ks NuSTAR observation of the z ∼ 2 hot dust-obscured galaxy (hot DOG) W1835+4355. We extracted spectra from the two NuSTAR detectors and analyzed them jointly with the archival XMM-Newton PN and MOS spectra. We performed a spectroscopic analysis based on both phenomenological and physically motivated models employing toroidal and spherical geometry for the obscurer. In all the modelings, the source exhibits a Compton-thick column density NH ≳ 1024 cm−2, a 2–10 keV luminosity L2−10 ≈ 2 × 1045 erg s−1, and a prominent soft excess (∼5–10% of the primary radiative output), which translates into a luminosity ∼1044 erg s−1. We modeled the spectral energy distribution from 1.6 to 850 μm using a clumpy two-phase dusty torus model plus a modified blackbody to account for emission powered by star formation in the far-infrared. We employed several geometrical configurations consistent with those applied in the X-ray analysis. In all cases we obtained a bolometric luminosity Lbol ≈ 3–5 × 1047 erg s−1, which confirms the hyperluminous nature of this active galactic nucleus. Finally, we estimate a prodigious star formation rate of ∼3000 M⊙ yr−1, which is consistent with the rates inferred for z ≈ 2–4 hyperluminous type I quasars. The heavily obscured nature, together with Lbol, the ratio of X-ray to mid-infrared luminosity, the rest-frame optical morphology, and the host star formation rate are indicative of its evolutionary stage. We can interpret this as a late-stage merger event in the transitional, dust-enshrouded, evolutionary phase eventually leading to an optically bright AGN.

Probing AGN inner structure with X-ray obscured type 1 AGN

Using the X-ray-selected active galactic nuclei (AGN) from the XMM-XXL north survey and the SDSS Baryon Oscillation Spectroscopic Survey (BOSS) spectroscopic follow-up of them, we compare the properties of X-ray unobscured and obscured broad-line AGN (BLAGN1 and BLAGN2; $N_\textrm{H}$below and above $10^{21.5}$ cm$^{-2}$), including their X-ray luminosity $L_X$, black hole mass, Eddington ratio $\lambda_{\textrm{Edd}}$, optical continuum and line features. We find that BLAGN2 have systematically larger broad line widths and hence apparently higher (lower) $M_{\textrm{BH}}$ ($\lambda_{\textrm{Edd}}$) than BLAGN1. We also find that the X-ray obscuration in BLAGN tends to coincide with optical dust extinction, which is optically thinner than that in narrow-line AGN (NLAGN) and likely partial-covering to the broad line region. All the results can be explained in the framework of a multi-component, clumpy torus model by interpreting BLAGN2 as an intermediate type between BLAGN1 and NLAGN in terms of an intermediate inclination angle.

The Emission and Distribution of Dust of the Torus of NGC 1068

Abstract We present observations of NGC 1068 covering the 19.7–53.0 μm wavelength range using FORCAST and HAWC+ on board SOFIA. Using these observations, high-angular-resolution infrared (IR) and submillimeter observations, we find an observational turnover of the torus emission in the 30–40 μm wavelength range with a characteristic temperature of 70–100 K. This component is clearly different from the diffuse extended emission in the narrow line and star formation regions at 10–100 μm within the central 700 pc. We compute 2.2–432 μm 2D images using the best inferred clumpy torus model based on several nuclear spectral energy distribution (SED) coverages. We find that when 1–20 μm SED is used, the inferred result gives a small torus size (&lt;4 pc radius) and a steep radial dust distribution. The computed torus using the 1–432 μm SED provides comparable torus sizes, pc radius, and morphology to the recently resolved 432 μm Atacama Large Millimeter Array observations. This result indicates that the 1–20 μm wavelength range is not able to probe the full extent of the torus. The characterization of the turnover emission of the torus using the 30–60 μm wavelength range is sensitive to the detection of cold dust in the torus. The morphology of the dust emission in our 2D image at 432 μm is spatially coincident with the cloud distribution, while the morphology of the emission in the 1–20 μm wavelength range shows an elongated morphology perpendicular to the cloud distribution. We find that our 2D clumpy torus image at 12 μm can produce comparable results to those observed using IR interferometry.

EW[OIII] as an Orientation Indicator for Quasars: Implications for the Torus

We present an analysis of the average spectral properties of 12,000 SDSS quasars as a function of accretion disc inclination, as measured from the equivalent width of the [OIII] 5007A line. The use of this indicator on a large sample of quasars from the SDSS DR7 has proven the presence of orientation effects on the features of UV/optical spectra, confirming the presence of outflows in the NLR gas and that the geometry of the BLR is disc-like. Relying on the goodness of this indicator, we are now using it to investigate other bands/components of AGN. Specifically, the study of the UV/optical/IR SED of the same sample provides information on the obscuring “torus.” The SED shows a decrease of the IR fraction moving from face-on to edge-on sources, in agreement with models where the torus is co-axial with the accretion disc. Moreover, the fact we are able to observe the broad emission lines also in sources in an edge-on position, suggests that the torus is rather clumpy than smooth as in the Unified Model. The behavior of the SED as a function of EW[OIII] is in agreement with the predictions of the clumpy torus models as well.

A mid-infrared statistical investigation of clumpy torus model predictions

We present new calculations of the CAT3D clumpy torus models, which now include a more physical dust sublimation model as well as AGN anisotropic emission. These new models allow graphite grains to persist at temperatures higher than the silicate dust sublimation temperature. This produces stronger near-infrared emission and bluer mid-infrared (MIR) spectral slopes. We make a statistical comparison of the CAT3D model MIR predictions with a compilation of sub-arcsecond resolution ground-based MIR spectroscopy of 52 nearby Seyfert galaxies (median distance of 36 Mpc) and 10 quasars. We focus on the AGN MIR spectral index $\alpha_{MIR}$ and the strength of the 9.7 $\mu$m silicate feature $S_{Sil}$. As with other clumpy torus models, the new CAT3D models do not reproduce the Seyfert galaxies with deep silicate absorption ($S_{Sil}<-1$). Excluding those, we conclude that the new CAT3D models are in better agreement with the observed $\alpha_{MIR}$ and $S_{Sil}$ of Seyfert galaxies and quasars. We find that Seyfert 2 are reproduced with models with low photon escape probabilities, while the quasars and the Seyfert 1-1.5 require generally models with higher photon escape probabilities. Quasars and Seyfert 1-1.5 tend to show steeper radial cloud distributions and fewer clouds along an equatorial line-of-sight than Seyfert 2. Introducing AGN anisotropic emission besides the more physical dust sublimation models alleviates the problem of requiring inverted radial cloud distributions (i.e., more clouds towards the outer parts of the torus) to explain the MIR spectral indices of type 2 Seyferts.

Survival of the Obscuring Torus in the Most Powerful Active Galactic Nuclei

Abstract Dedicated searches generally find a decreasing fraction of obscured active galactic nuclei (AGN) with increasing AGN luminosity. This has often been interpreted as evidence for a decrease of the covering factor of the AGN torus with increasing luminosity, the so-called receding torus models. Using a complete flux-limited X-ray selected sample of 199 AGN, from the Bright Ultra-hard XMM-Newton Survey, we determine the intrinsic fraction of optical type-2 AGN at as a function of rest-frame 2–10 keV X-ray luminosity from to . We use the distributions of covering factors of AGN tori derived from CLUMPY torus models. Since these distributions combined over the total AGN population need to match the intrinsic type-2 AGN fraction, we reveal a population of X-ray undetected objects with high-covering factor tori, which are increasingly numerous at higher AGN luminosities. When these “missing” objects are included, we find that Compton-thick AGN account at most for % of the total population. The intrinsic type-2 AGN fraction is 58 ± 4% and has a weak, non-significant (less than 2σ) luminosity dependence. This contradicts the results generally reported by AGN surveys and the expectations from receding torus models. Our findings imply that the majority of luminous rapidly accreting supermassive black holes at reside in highly obscured nuclear environments, but most of them are so deeply embedded that they have so far escaped detection in X-rays in &lt;10 keV wide area surveys.

Hints on the Gradual Resizing of the Torus in AGNs through Decomposition of Spitzer/IRS Spectra

Abstract Several authors have claimed that less luminous active galactic nuclei (AGNs) are not capable of sustaining a dusty torus structure. Thus, a gradual resizing of the torus is expected when the AGN luminosity decreases. Our aim is to examine mid-infrared observations of local AGNs of different luminosities for the gradual resizing and disappearance of the torus. We applied the decomposition method described by Hernán-Caballero et al. to a sample of ∼100 Spitzer/IRS spectra of low-luminosity AGNs and powerful Seyferts in order to decontaminate the torus component from other contributors. We have also included Starburst objects to ensure secure decomposition of the Spitzer/IRS spectra. We have used the affinity propagation (AP) method to cluster the data into five groups within the sample according to torus contribution to the 5–15 μm range ( ) and bolometric luminosity ( ). The AP groups show a progressively higher torus contribution and an increase of the bolometric luminosity from Group 1 ( and ) up to Group 5 ( and ). We have fitted the average spectra of each of the AP groups to clumpy models. The torus is no longer present in Group 1, supporting its disappearance at low luminosities. We were able to fit the average spectra for the torus component in Groups 3 ( and ), 4 ( and ), and 5 to Clumpy torus models. We did not find a good fitting to Clumpy torus models for Group 2 ( and ). This might suggest a different configuration and/or composition of the clouds for Group 2, which is consistent with the different gas content seen in Groups 1, 2, and 3, according to detections of molecular lines. Groups 3, 4, and 5 show a trend of decreasing torus width (which leads to a likely decrease of the geometrical covering factor), although we cannot confirm it with the present data. Finally, Groups 3, 4, and 5 show an increase of the outer radius of the torus for higher luminosities, consistent with a resizing of the torus according to AGN luminosity.

Dusty Winds in Active Galactic Nuclei: Reconciling Observations with Models

Abstract This Letter presents a revised radiative transfer model for the infrared (IR) emission of active galactic nuclei (AGNs). While current models assume that the IR is emitted from a dusty torus in the equatorial plane of the AGNs, spatially resolved observations indicate that the majority of the IR emission from ≲100 pc in many AGNs originates from the polar region, contradicting classical torus models. The new model CAT3D-WIND builds upon the suggestion that the dusty gas around the AGNs consists of an inflowing disk and an outflowing wind. Here, it is demonstrated that (1) such disk+wind models cover overall a similar parameter range of observed spectral features in the IR as classical clumpy torus models, e.g., the silicate feature strengths and mid-IR spectral slopes, (2) they reproduce the 3–5 μm bump observed in many type 1 AGNs unlike torus models, and (3) they are able to explain polar emission features seen in IR interferometry, even for type 1 AGNs at relatively low inclination, as demonstrated for NGC3783. These characteristics make it possible to reconcile radiative transfer models with observations and provide further evidence of a two-component parsec-scale dusty medium around AGNs: the disk gives rise to the 3–5 μm near-IR component, while the wind produces the mid-IR emission. The model SEDs will be made available for download.

The dusty tori of nearby QSOs as constrained by high-resolution mid-IR observations

We present mid-infrared (MIR, 7.5-13.5 $\mu$m) imaging and spectroscopy observations obtained with the CanariCam (CC) instrument on the 10.4m Gran Telescopio CANARIAS for a sample of 20 nearby, MIR bright and X-ray luminous QSOs. We find that for the majority of QSOs the MIR emission is unresolved at angular scales nearly 0.3 arcsec, corresponding to physical scales $<600$ pc. We find that the higher-spatial resolution CC spectra have similar shapes to those obtained with Spitzer/IRS, and hence we can assume that the spectra are not heavily contaminated by extended emission in the host galaxy. We thus take advantage of the higher signal to noise Spitzer/IRS spectra, as a fair representation of the nuclear emission, to decompose it into a combination of active galactic nuclei (AGN), polycyclic aromatic hydrocarbon (PAH) and stellar components. In most cases the AGN is the dominant component, with a median contribution of 85 per cent of the continuum light at MIR (5-15 $\mu$m) within the IRS slit. This IR AGN emission is well reproduced by clumpy torus models. We find evidence for significant differences in the parameters that describe the dusty tori of QSOs when compared with the same parameters of Seyfert 1 and 2 nuclei. In particular, we find a lower number of clouds ($N_{0}<12$), steeper radial distribution of clouds ($q=1.5-3.0$), and clouds that are less optically thick ($\tau_{V}<100$) than in Seyfert 1, which could be attributed to dusty structures that have been partially evaporated and piled up by the higher radiation field in QSOs. We find that the combination of the angular width $\sigma_{torus}$, viewing angle $i$, and number of clouds along the equatorial line $N_{0}$, produces large escape probabilities ($P_{esc} > 2$ per cent) and low geometrical covering factors ($f_{2}<0.6$), as expected for AGN with broad lines in their optical spectra.

Ground-based Mid-infrared Study of the Compton-thick AGN in M51 at 10–100 pc Scale*

Abstract We performed near-diffraction-limited ( FWHM) N-band imaging of one of the nearest active galactic nuclei (AGNs) in M51 with the 8.2 m Subaru Telescope to study the nuclear structure and spectral energy distribution (SED) at 8–13 μm. We found that the nucleus is composed of an unresolved core (at pc resolution, orintrinsic size corrected for the instrumental effect of pc) and an extended halo (at a few tens of parsec scale), and each of their SEDs is almost flat. We examined the SED by comparing with the archival Spitzer IRS spectrum processed to mimic our chopping observation of the nucleus and the published radiative transfer model SEDs of the AGN clumpy dusty torus. The halo SED is likely due to circumnuclear star formation showing deficient polycyclic aromatic hydrocarbon emission due to the AGN. The core SED is likely dominated by the AGN because of the following two reasons. First, the clumpy torus model SEDs can reproduce the red mid-infrared continuum with apparently moderate silicate 9.7 μm absorption. Second, the core 12 μm luminosity and the absorption-corrected X-ray luminosity at 2–10 keV in the literature follow the mid-infrared–X-ray luminosity correlation known for the nearby AGNs, including the Compton-thick ones.

Magnetohydrodynamic disc winds and line width distributions – II

We study AGN emission line profiles combining an improved version of the accretion disc-wind model of Murray & Chiang with the magnetohydrodynamic (MHD) model of Emmering et al. Here, we extend our previous work to consider central objects with different masses and/or luminosities. We have compared the dispersions in our model C iv line-width distributions to observational upper limit on that dispersion, considering both smooth and clumpy torus models. Following Fine et al., we transform that scatter in the profile line-widths into a constraint on the torus geometry and show how the half-opening angle of the obscuring structure depends on the mass of the central object and the accretion rate. We find that the results depend only mildly on the dimensionless angular momentum, one of the two integrals of motion that characterize the dynamics of the self-similar ideal MHD outflows.