Structure and Kinematics of the Broad-Line Region and Torus of Active Galactic Nuclei
C. Martin Gaskell, Rene W. Goosmann, Elizabeth S. Klimek
备注：
Talk given at "The Central Kiloparsec: Active Galactic Nuclei and Their Hosts", Ierapetra, Crete, 4-6 June, 2008. To appear in Volume 79 of the Memorie della Societa Astronomica Italiana. 6 pages, 3 figures
Energetics considerations imply that the broad-line region (BLR) has a high covering factor. The absence of absorption from the BLR means that the BLR has to have a flattened distribution and be seen through a polar hole. The BLR is the inward extension of the torus and they have similar geometries and covering factors. Reconciling velocity-resolved reverberation mapping, spectropolarimetry, and the increasing blueshifting of BLR lines with decreasing distance from the centre, implies that the BLR has a significant inflow component. This inflow provides the mass inflow rate needed to power the AGN. We suggest that the mechanism producing the outward transport of angular momentum necessary for the net inflow of the BLR is the magneto-rotational instability, and that the BLR and outer accretion disc are one and the same.
The presence of obscuring material (or a dusty `torus') in active galactic nuclei (AGN) is central to the unification model for AGN. Two models, the multi-population model for radio sources and the receding torus model, are capable of describing observational properties of powerful radio galaxies and radio quasars. Here, I study the changes of the opening angle of the obscuring torus with radio luminosity at 151 MHz, [O III] emission-line luminosity and cosmic epoch aiming to discriminate between two working models. An analytical expression relating the half opening angle of the torus to the m…
We propose a new diagnostic of the ``dusty torus'' model for Seyfert nuclei. Dust grains in the torus are heated by the nuclear continuum, and reradiate mostly in the mid-infrared wavelengths. From the torus geometry, it is predicted that the emission at lambda < 10 micron has strong dependence on the viewing angle. Since the dependence is predicted to be insignificant at lambda > 10 micron, we study the flux ratio between 3.5 micron (L band) and 25 micron; R(L,25) = log [(nu_3.5 um S_nu_3.5 um)/(nu_25 um S_nu_25 um)]. In three different samples (optically selected, X-ray selected, and infrare…
A geometrically thick dusty torus in NGC 1068 has been unambiguously resolved by an infrared interferometry telescope. This implies clouds composing the dusty torus are undergoing supersonic collisions with each other. We show that the collisions form strong non-relativistic shocks, which accelerate populations of relativistic electrons. Torus reprocesses emission from accretion disk into infrared band. We show that the energy density of the infrared photons inside the torus is much higher than that of the magnetic field in the clouds and the seed photons of inverse Compton scattering are main…
Geometrical and physical properties of dusty tori of Seyfert nuclei probed by the water vapor maser emission at 22 GHz are discussed. We assume that the dusty torus has a simple cylindrical form and the maser emission can be detected only when we observe the torus from almost edge-on views. The observed low frequency of occurrence of the water vapor maser emission (less than 10 percent) suggests that the torus is a vertically thin cylinder whose outer radius between a few pc and ~ 10 pc. However, the observed masing regions are concentrated in the inner 1 pc regions of the torus. This property…
The torus concept as an essential structural component of active galactic nuclei (AGN) is generally accepted. Here, the situation is discussed when the torus "twisting" by the radiation or wind transforms it into a dipole toroidal vortex which in turn can be a source of matter replenishing the accretion disk. Thus emerging instability which can be responsible for quasar radiation flares accompanied by matter outbursts is also discussed. The "Matreshka" scheme for an obscuring vortex torus structure capable of explaining the AGN variability and evolution is proposed. The model parameters estima…
I present polarization modelling of Active Galactic Nuclei in the optical/UV range. The modelling is conducted using the Monte-Carlo radiative transfer code Stokes, which self-consistently models the polarization signature of a complex model arrangement for an active nucleus. In this work I include three different scattering regions around the central source: an equatorial electron scattering disk, an equatorial obscuring dusty torus, and polar electron scattering cones. I investigate the resulting dependencies of the V-band polarization for different optical depths of the scattering cones, di…
The kinematics of jets in active galactic nuclei (QSOs, BL Lacs, Radio Galaxies and Empty Field objects) on parsec scales is being studied with Very Long Baseline Array observations at 15 GHz of a sample of more than 170 radio sources. More than 1000 images have been taken since 1994. Here we present an overview of the results of our study, including the proper motions of components in the jets, and their relationship with other source properties.
Having found that type 1 Seyfert nuclei have excess [FeVII]6087 emission with respect to type 2s, Murayama & Taniguchi have proposed that the high-ionization nuclear emission-line region (HINER) traced by the [FeVII]6087 emission resides in the inner wall of dusty tori. The covering factor of the torus is usually large (e.g., ~ 0.9). Further, electron density in the tori (e.g., ~ 10^7-10^8 cm-3) is considered to be higher significantly than that (e.g., ~ 10^3-10^4 cm^-3) in the narrow-line region (NLR). Therefore it is expected that the torus emission contributes to the majority of the higher-…
We describe improved modelling of the emission by dust in a toroidal--like structure heated by a central illuminating source within Active Galactic Nuclei (AGN). We chose a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type-1 AGN. We exploit this model to study the spectral ene…
We describe the results of a detailed study of the polarization properties of the broad H-alpha emission line in Type 1 Seyfert nuclei. Our analysis of these data points to a model in which the broad Balmer lines are emitted by a rotating disk, and are scattered in two main regions - one co-planar with the disk and within the circum-nuclear torus, the other, the polar scattering region, outside the torus but aligned with its axis. The relative importance of the two sources of polarized light is largely determined by the inclination of the system axis to the line-of-sight.
We present the first systematic investigation of the [NeV] (14um/24um) and [SIII] (18um/33um) infrared line flux ratios, traditionally used to estimate the density of the ionized gas, in a sample of 41 Type 1 and Type 2 active galactic nuclei (AGNs) observed with the Infrared Spectrograph on board Spitzer. The majority of galaxies with both [NeV] lines detected have observed [NeV] line flux ratios consistent with or below the theoretical low density limit, based on calculations using currently available collision strengths and ignoring absorption and stimulated emission. We find that Type 2 AG…
We report the new finding that type 1 Seyfert nuclei (S1s) have excess [FeVII]6087 emission with respect to type 2s (S2s). The S1s exhibit broad emission lines which are attributed to ionized gas within 1 pc of the black hole, whereas the S2s do not show such broad lines. The current unified model of active galactic nuclei explains this difference as that the central 1 pc region in the S2s is hidden from the line of sight by a dusty torus if we observe it from a nearly edge-on view toward the torus. Therefore, our finding implies that the coronal line region (CLR) traced by the [FeVII]6087 emi…
We assemble a sample consisting of 66 active galactic nuclei (AGNs) from literature and the {\em XMM-Newton} archive in order to investigate the origin of the 6.4 keV narrow iron K$α$ line (NIKAL). The X-ray Baldwin effect of the NIKAL is confirmed in this sample. We find the equivalent width ($EW$) of the NIKAL is more strongly inversely correlated with Eddington ratio ($\ce$) than the 2-10 keV X-ray luminosity. Our sample favors the origin from the dusty torus and the X-ray Baldwin effect is caused by the changing opening angle of the dusty torus. The relation $EW-\ce$ can be derived from a …
Recently, Maiolino et al. (2001a, A&A, 365, 28) constructed a sample of active galactic nuclei for which both the reddening E(B-V) and the column density N_H to the nucleus could be determined. For most of the galaxies in their sample, they found that E(B-V)/N_H is substantially smaller than for the diffuse ISM of our Galaxy. They asserted that either the dust-to-gas ratio is lower than in the Galaxy or that the grains are so large that they do not extinct or redden efficiently in the optical. We show that there is no systematic increase in E(B-V) with N_H for the Maiolino et al. (2001a) galax…
We report the results of a Submillimeter Array (SMA) interferometric observation of 21-micron source IRAS 07134+1005 in the CO J=3-2 line. In order to determine the morpho-kinematic properties of the molecular envelope of the object, we constructed a model using the Shape software to model the observed CO map. We find that the molecular gas component of the envelopes can be interpreted as a geometrically thick expanding torus with an expanding velocity of 8 km/s. The inner and outer radii of the torus determined by fitting Shape models are 1.2" and 3.0", respectively. The inner radius is consi…
We explore physically self-consistent models of dusty molecular tori in Active Galactic Nuclei (AGN) with the goal of interpreting VLTI observations and fitting high resolution mid-IR spectral energy distributions (SEDs). The input dust distribution is analytically calculated by assuming hydrostatic equilibrium between pressure forces - due to the turbulent motion of the gas clouds - and gravitational and centrifugal forces as a result of the contribution of the nuclear stellar distribution and the central black hole. For a fully three-dimensional treatment of the radiative transfer problem th…
Unified schemes of active galactic nuclei (AGN) require an obscuring dusty torus around the central source, giving rise to Seyfert 1 line spectrum for pole-on viewing and Seyfert 2 characteristics in edge-on sources. Although the observed IR is in broad agreement with this scheme, the behavior of the 10 micron silicate feature and the width of the far-IR emission peak remained serious problems in all previous modeling efforts. We show that these problems find a natural explanation if the dust is contained in about 5-10 clouds along radial rays through the torus. The spectral energy distributio…
Deep surveys of {\em Chandra} and {\em HST} (Hubble Space Telescope) show that active galactic nucleus (AGN) populations are changing with hard X-ray luminosities. This arises an interesting question whether the dusty torus is evolving with the central engines. We assemble a sample of 50 radio-quiet PG quasars to tackle this problem. The covering factors of the dusty tori can be estimated from the multiwavelength continuum. We find they are strongly correlated with the hard X-ray luminosity. Interestingly this correlation agrees with the fraction of type II AGNs discovered by {\em Chandra} and…
Observations give strong support for the unification scheme of active galactic nuclei. The scheme is premised on toroidal obscuration of the central engine by dusty clouds that are individually very optically thick. These lectures summarize the torus properties, describe the handling and implications of its clumpy nature and present speculations about its dynamic origin.
The structure of obscuring matter in the environment of active galactic nuclei with associated nuclear starbursts is investigated using 3-D hydrodynamical simulations. Simple analytical estimates suggest that the obscuring matter with energy feedback from supernovae has a torus-like structure with a radius of several tens of parsecs and a scale height of about 10 pc. These estimates are confirmed by the fully non-linear numerical simulations, in which the multi-phase inhomogeneous interstellar matter and its interaction with the supernovae are consistently followed. The globally stable, torus-…
X-ray observations with Chandra and XMM-Newton have shown that there are relatively narrow cores to the iron K-alpha emission lines in active galactic nuclei (AGN). Plausible origins for this core emission include the outer regions of an accretion disk, a pc-scale molecular torus, and the optical broad-line region (BLR). Using data from the literature it is shown that no correlation exists between the Fe K-alpha core width and the BLR (specifically H-beta) line width. This shows that in general the iron K-alpha core emission does not arise from the BLR. There is a similar lack of correlation b…
Unified schemes of active galactic nuclei (AGN) require an obscuring dusty torus around the central engine. Torus sizes of hundreds of parsecs were deduced from early theoretical modeling efforts, but high-resolution IR observations now show that the torus size is no more than a few parsecs. This conflict is resolved when the clumpy nature of the torus is taken into account. The compact torus may be best understood when identified with the dusty, optically thick region of the wind coming off the central accretion disk.
We build and test Parker-wind models to apply to observations of large-scale (of order 100 pc) outflows from Active Galactic Nuclei (AGNs). These models include detailed photoionization simulations, the observed radially varying mass profile, adiabatic cooling, and approximations for clouds dragged along in the wind and the interaction of the wind with the circumnuclear ISM of the galaxy. We test this model against recent HST/STIS observations of [O III] emission-line kinematics (in particular, we test against those observed in NGC 4151, but approximately the same kinematics is observed in NGC…
To investigate the relationship between black holes and their host galaxies, many groups have used the width of the [O III] 5007 line as a substitute for the stellar velocity dispersion (sigma*) of galaxy bulges. We directly test this assumption with a large and homogeneous sample of narrow-line active galactic nuclei from the Sloan Digital Sky Survey. We consider multiple transitions ([O II] 3727, [O III] 5007, and [S II] 6716, 6731) and various techniques for quantifying the line width in order to obtain a calibration between the gas velocity dispersion, sigma_g, and sigma*. We find that sig…
Expansion velocities (Vexp) of different ions and line widths at the base of the lines are measured and analyzed for 24 PNe with [WC]-type nuclei (WRPNe), 9 PNe ionized by WELS (WLPNe) and 14 ordinary PNe. A comparative study of the kinematical behavior of the sample clearly demonstrates that WRPNe have in average 40-45% larger Vexp, and possibly more turbulence than WLPNe and ordinary PNe. WLPNe have velocity fields very much alike the ones of ordinary PNe, rather than the ones of WRPNe. All the samples (WRPNe, WLPNe and ordinary PNe) show expansion velocities increasing with age indicators, …
High-resolution imaging and long-slit spectroscopy obtained with HST, combined with ground-based integral-field spectroscopy, provides the kinematics of stars and gas in nearby galactic nuclei with sufficient accuracy to derive the intrinsic dynamical structure, and to measure the mass of the central black hole. This has revealed that many nuclei contain decoupled kinematic components and asymmetric structures, and that nuclear and global properties of galaxies are correlated. Higher spatial resolution and significantly increased sensitivity are required to cover the full range of galaxy prope…
Using a spectrum obtained under moderate (of order 1 arcsecond) seeing, we show that the double nucleus in M31 produces a strong kinematic signature even though the individual components are not spatially resolved. The signature consists of a significant asymmetric wing in the stellar velocity distribution close to the center of the system. The properties of the second nucleus derived from this analysis agree closely with those measured from high-spatial resolution Hubble Space Telescope images. Even Space Telescope only has sufficient resolution to study the structure of very nearby galactic …
Half of the Seyfert-2 galaxies escaped detection of broad lines in their polarised spectra observed so far. Some authors have suspected that these non-HBLRs contain real Sy2 nuclei without intrinsic broad line region hidden behind a dust torus. If this were true, then their nuclear structure would fundamentally differ from that of Sy2s with polarised broad lines: in particular, they would not be explained by orientation-based AGN unification. Further arguments for two physically different Sy2 populations have been derived from the warm and cool IRAS F25/F60 ratios. These ratios, however, refer…
We analyze X-ray spectra of heavily obscured (N_H > 10^{24} cm^{-2}) active galaxies obtained with Chandra, concentrating on the iron K alpha fluorescence line. We measure very large equivalent widths in most cases, up to 5 keV in the most extreme example. The geometry of an obscuring torus of material near the active galactic nucleus (AGN) determines the Fe emission, which we model as a function of torus opening angle, viewing angle, and optical depth. The starburst/AGN composite galaxies in this sample require small opening angles. Starburst/AGN composite galaxies in general therefore presen…
Motivated by unification schemes of active galactic nuclei, we review evidence for the existence of a small-scale dust torus in M87, a Fanaroff-Riley Class I radio galaxy. Since there is no direct evidence of any thermal emission from its torus we consider indirect evidence, such as BLR activity and ageing arguments to model the cold dust structure of M87. In the context of the jet -- accretion disk -- torus symbiosis we discuss the interactions of GeV and TeV gamma-rays produced in the jet of M87 with the infrared radiation fields external to the jet, produced by a less active torus. A thin a…
Here we report on observations of powerful hydroxyl (OH) line emissions that trace the obscuring material within the circumnuclear environment of the galaxy Markarian 231. The hydroxyl (mega)-maser emission shows the characteristics of a rotating, dusty, molecular torus (or thick disk) located between 30 and 100 pc from the central engine. We now have a clear view of the physical conditions, the kinematics and the spatial structure of this material on intermediate size scales, confirming the main tenets of unification models.
We present spectra of 6 type 1 Seyfert galaxies, 2 Seyfert 2, a starburst galaxy and a compact narrow line radiogalaxy, taken in two spectral ranges centered around the near--IR CaII triplet (CaT) (at ~8600 Angstroms), and the Mgb stellar feature at 5180 Angstroms. We measured the equivalent width (EWs) of these features and the Fe52 and Fe53 spectral indices. We found that the strength of the CaT in type 1 Seyfert galaxies with prominent central point sources, is larger than what would be expected from the observed strength of the blue indices. This could be explained by the presence of red s…
Massive nuclear black holes of 10^6 - 10^9 solar masses are believed to be responsible for the the energy production in quasars and active galaxies, and are thought to be present in many quiescent galaxies as well. Dynamical evidence for this can be sought by studying the dynamics of gas and stars in galactic nuclei at high spatial resolution. This paper reviews the current evidence, with emphasis on some recent developments and ongoing projects. The evidence from water masers and gas kinematics in the active galaxies NGC 4258 and M87 is compelling. In quiescent galaxies only stellar kinematic…
Several studies of nearby active galaxies indicate significantly higher HCN-to-CO intensity ratios in AGN than in starburst (SB) environments. HCN enhancement can be caused by many different effects, such as higher gas densities/temperatures, UV/X-ray radiation, and non-collisional excitation. As active galaxies often exhibit intense circumnuclear SB, high angular resolution/sensitivity observations are of paramount importance to disentangling the influence of SB from that of nuclear activity on the chemistry of the surrounding molecular gas. The tight relation of HCN enhancement and nuclear a…
Observations give strong support for the unification scheme of active galactic nuclei. Clumpiness of the toroidal obscuration is crucial for explaining the IR observations and has significance consequences for AGN classification: type 1 and type 2 viewing is an angle-dependent probability, not an absolute property. The broad line region (BLR) and the dusty torus are, respectively, the inner and outer segments, across the dust sublimation radius, of a continuous cloud distribution. Continuum X-ray obscuration comes mostly from the inner, BLR clouds. All clouds are embedded in a disk wind, whose…
In order to constrain the properties of dense and warm gas around active galactic nuclei, we have searched Infrared Space Observatory spectra of local active galactic nuclei for the signature of the 4.7micron fundamental ro-vibrational band of carbon monoxide. Low resolution spectra of 31 AGN put upper limits on the presence of wide absorption bands corresponding to absorption by large columns of warm and dense gas against the nuclear dust continuum. High resolution (R~2500) spectra of NGC 1068 detect no significant absorption or emission in individual lines, to a 3sigma limit of 7% of the con…
We have identified 12 Seyfert 1 galaxies that exhibit optical polarization spectra similar to those of Seyfert 2 galaxies in which polarized broad-lines are detected. We present new spectropolarimetric observations of 3 of them: Was 45, Mrk 231 and NGC 3227. These objects appear to be polarized as a result of far-field scattering in the polar illumination cones of the circum-nuclear torus. We estimate that they represent between 10 and 30 per cent of the Seyfert 1 population; they are found amongst all the main spectroscopic sub-types, including narrow-line Seyfert 1 galaxies. We have shown el…
Recent VLBI observations have identified several compact radio sources which have symmetric structures on parsec scales, and exhibit HI absorption which appears to be associated with the active nucleus. These sources are uniquely well suited to investigations into the physics of the central engines, in particular to studies of the kinematics of the gas within 100 pc of the core. In these compact sources, it is reasonable to assume that this circumnuclear material is accreting onto, and ``feeding'', the central engine. We present results of HI imaging studies of 3 symmetric radio galaxies which…
Masses of black holes in nearby galactic nuclei can be measured in a variety of ways, using stellar and gaseous kinematics. Reliable black hole masses are known for several dozen objects, so that demographic questions can start to be addressed with some confidence. Prospects for the near future are discussed briefly.
We show from modeling the Fe Kalpha line in the ASCA spectra of four X-ray bright narrow emission line galaxies (Seyfert types 1.9 and 2) that two equally viable physical models can describe the observed line profile. The first is discussed by Turner et al. (1998) and consists of emission from a nearly pole-on accretion disk. The second, which is statistically preferred, is a superposition of emission from an accretion disk viewed at an intermediate inclination of about 48 degrees and a distinct, unresolved feature that presumably originates some distance from the galaxy nucleus. The intermedi…
The masses of the central black holes of Active Galactic Nuclei estimated by the reverberation virial technique seem to be significantly smaller than predicted from the black hole mass-bulge luminosity relation for massive black holes detected by kinematic methods in less active and normal galaxies. We reexamine the relation for updated data and suggest a few reasons that may cause this discrepancy.
We have calculated a series of models of outflows from the obscuring torus in active galactic nuclei (AGN). Our modeling assumes that the inner face of a rotationally supported torus is illuminated and heated by the intense X-rays from the inner accretion disk and black hole. As a result of such heating a strong biconical outflow is observed in our simulations. We calculate 3-dimensional hydrodynamical models, assuming axial symmetry, and including the effects of X-ray heating, ionization, and radiation pressure. We discuss the behavior of a large family of these models, their velocity fields,…
This paper summarizes the observations which provide the best evidence for the presence of black holes in active galactic nuclei. This includes: X-ray variability; kinematical studies using optical emission lines as well as the distribution of megamaser spots; and the shape of the Fe K$α$ X-ray emission line. It also presents the current status of our understanding of jet-dominated active galaxies (blazars), and briefly reviews the currently popular AGN ``Unification Schemes.''
We have analyzed HST spectroscopy of 24 nearby AGNs to investigate spatially-resolved gas kinematics in the Narrow Line Region (NLR). These observations effectively isolate the nuclear line profiles on less than 100 pc scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion sigma_* of the host galaxy, a quantity which relates with substantially less scatter to the mass of the central, supermassive black hole, and more generally characterize variations in the NLR velocity field with radius. We find that …
First results from the AGN-Heidelberg program aimed at spatially resolving the central pc region of the closest Active Galactic Nuclei are presented. The core region of prototype active nuclei are clearly unveiled at IR waves and at distances from the nucleus - few pc- where circumnuclear starforming regions appear not to be present. Within that perspective, classical active nuclei as Circinus and NGC 1097, reveal with unprecedented detail clear channels of material being driven to the core whereas others as Centaurus A and NGC 1566, show a "clean" core environment. At the very center, a centr…
Many theories for the formation of massive black holes in galactic nuclei predict that the stellar motions should be anisotropic within the radius of influence of the black hole. We report tentative evidence for such an effect in M87.
We consider the consequences of gravitational wave recoil for unified models of active galactic nuclei (AGNs). Spatial oscillations of supermassive black holes (SMBHs) around the cores of galaxies following gravitational wave (GW) recoil imply that the SMBHs spend a significant fraction of time off-nucleus, at scales beyond that of the molecular obscuring torus. Assuming reasonable distributions of recoil velocities, we compute the off-core timescale of (intrinsically type-2) quasars. We find that roughly one-half of major mergers result in a SMBH being displaced beyond the torus for a time of…
