Molecular tori in Seyfert galaxies - Feeding the monster and hiding it

Krolik, Julian H.; Begelman, Mitchell C.

doi:10.1086/166414

Cited by 555 publications

(600 citation statements)

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“…If the X-ray source is partially covered by Compton-thick material, the reflected component would in fact have a stronger relative influence over the continuum. Krolik & Begelman (1988) showed that a torus with a smooth dust distribution cannot survive close to the AGN, and proposed that the material is distributed in a clumpy structure. Mid-infrared spectra of Seyfert galaxies have been proven to be consistent with the clumpy torus scenario (e.g., Mor et al 2009).…”

Section: Seyfert Galaxies: the Reflection Componentmentioning

confidence: 99%

Reflection in Seyfert galaxies and the unified model of AGN

Ricci

Walter

Courvoisier

et al. 2011

A&A

128

143

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We present a deep study of the average hard X-ray spectra of Seyfert galaxies. We aim to test the unified model of active galactic nuclei, and constrain differences and similarities between different classes of objects. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the 165 Seyfert galaxies detected at z < 0.2. Our final sample consists of 44 Seyfert 1s, 29 Seyfert 1.5s, 78 Seyfert 2s, and 14 narrow-line Seyfert 1s. For each subsample, we stacked all the images, and derived their average hard X-ray spectra in the 17-250 keV energy range. We performed a detailed spectral analysis using both a model-independent and a model-dependent approach. All classes of Seyfert galaxies show on average the same nuclear continuum, as foreseen by the zeroth order unified model, with a cutoff energy of E C 200 keV, and a photon index of Γ ≃ 1.8. The average optical depth of the Comptonizing medium is consistent for the different classes (τ ≃ 0.8). Compton-thin Seyfert 2s show a reflection component stronger than Seyfert 1s and Seyfert 1.5s. Most of this reflection is due to mildly obscured (10 23 cm −2 ≤ N H < 10 24 cm −2 ) Seyfert 2s, which have a significantly stronger reflection component (R = 2.2 +4.5 −1.1 ) than Seyfert 1s (R ≤ 0.4), Seyfert 1.5s (R ≤ 0.4) and lightly obscured (N H < 10 23 cm −2 ) Seyfert 2s (R ≤ 0.5). This cannot be explained easily by the unified model. The absorber/reflector in mildly obscured Seyfert 2s might cover a large fraction of the X-ray source, and contain clumps of Compton-thick material. The large reflection found in the spectrum of mildly obscured Seyfert 2s reduces the amount of Compton-thick objects needed to explain the peak of the cosmic X-ray background. Our results are consistent with the fraction of Compton-thick sources being ∼ 10%. The spectra of Seyfert 2s with and without polarized broad lines do not show significant differences, the only difference between the two samples being the higher hard X-ray and bolometric luminosity of Seyfert 2s with polarized broad lines. The average hard X-ray spectrum of narrow-line Seyfert 1s is steeper than those of Seyfert 1s and Seyfert 1.5s, probably due to a lower energy of the cutoff.

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Section: Seyfert Galaxies: the Reflection Componentmentioning

confidence: 99%

Reflection in Seyfert galaxies and the unified model of AGN

Ricci

Walter

Courvoisier

et al. 2011

A&A

128

143

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“…However, following the approach of Krolik (1999) who, for rough estimates, assumes thermal emission by spherical black bodies, the typical angular size of each component inside an AGN is given by the expression:…”

Section: Temperature Of the Midi Compact Componentmentioning

confidence: 99%

“…More recently, Schartmann et al (2005) described the three dimensional treatment of radiative transfer through dusty tori at hydrostatic equilibrium and succeed in reproducing both the mean large aperture spectra from UV to far-IR of several Seyfert type 1 galaxies, and the recent MIDI observations of two specified Seyfert type 2: Circinus and NGC 1068, except for the 9.7 µm silicate feature. Geometrical and dynamical properties of dusty tori have been theoretically investigated, among others, by Krolik & Begelman (1988), Zier & Biermann (2002), and Beckert & Duschl (2004).…”

Section: Introductionmentioning

confidence: 99%

A new analysis of the nucleus of NGC 1068 with MIDI observations

Poncelet

Perrin²,

Sol³

2006

A&A

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We present a new analysis of the first mid-infrared N-band long-baseline interferometric observations of an extragalactic source: the nucleus of the Seyfert 2 galaxy NGC 1068, obtained with MIDI (Mid-InfrareD Interferometer), the mid-infrared beamcombiner at the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI). The resolution of λ/B ∼ 10 mas allows us to study the compact central core of the galaxy between 8 and 13 µm. Both visibility measurements and MIDI spectrum are well reproduced by a simple radiative transfer model with two concentric spherical components. The derived angular sizes and temperatures are ∼35 and 83 mas, and ∼361 K and 226 K for these two components respectively. Other evidence strongly supports such low temperatures. This modeling also provides the variation of optical depth as a function of wavelength for the extended component across the N-band suggesting the presence of amorphous silicate grains. This shows that MIDI has carried out the first direct observations of the distribution of dust around the central engine.

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“…If this unification scenario is correct, infrared observations of the nuclei of radio galaxies may act as calorimeters that indicate the levels of accretion activity. The dust tori, believed to be clumpy and to extend out to radii of tens to hundreds of parsecs (Krolik & Begelman 1988;Nenkova et al 2002;Granato et al 1997;Shi et al 2006), reradiate the optical and ultraviolet emission originating from the accretion disks surrounding the supermassive black holes (>10 6 M ). However, only radio galaxies displaying high-excitation narrow-line optical emission, referred to as high-excitation radio galaxies (HEGs), are understood to host obscured broad line and bright continuum emission, and to be in the process of active black hole accretion (Barthel 1994;Laing et al 1994).…”

Section: Introductionmentioning

confidence: 99%

Dust tori in radio galaxies

Wolk¹,

Barthel²,

Peletier³

et al. 2010

A&A

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Aims. We investigate the quasar -radio galaxy unification scenario and detect dust tori within radio galaxies of various types. Methods. Using VISIR on the VLT, we acquired sub-arcsecond (∼0.40 ) resolution N-band images, at a wavelength of 11.85 μm, of the nuclei of a sample of 27 radio galaxies of four types in the redshift range z = 0.006−0.156. The sample consists of 8 edge-darkened, low-power Fanaroff-Riley class I (FR-I) radio galaxies, 6 edge-brightened, class II (FR-II) radio galaxies displaying low-excitation optical emission, 7 FR-IIs displaying high-excitation optical emission, and 6 FR-II broad emission line radio galaxies. Out of the sample of 27 objects, 10 nuclei are detected and several have constraining non-detections at sensitivities of 7 mJy, the limiting flux a point source has when detected with a signal-to-noise ratio of 10 in one hour of source integration. Results. On the basis of the core spectral energy distributions of this sample we find clear indications that many FR-I and several low-excitation FR-II radio galaxies do not contain warm dust tori. At least 57 ± 19 percent of the high-excitation FR-IIs and almost all of the broad line radio galaxies exhibit excess infrared emission, which must be attributed to warm dust reradiating accretion activity. The FR-I and low-excitation FR-II galaxies are all of low efficiency, which is calculated as the ratio of bolometric to Eddington luminosity L bol /L Edd < 10 −3 . This suggests that thick tori are absent at low accretion rates and/or low efficiencies. The high-excitation FR-II galaxies are a mixed population with three types of nuclei: 1) low efficiency with dust torus; 2) low efficiency with weakly emitting dust torus; and 3) high efficiency with weak dust torus. We argue that the unification viewing angle range 0-45 degrees of quasars should be increased to ∼60 degrees, at least at lower luminosities.

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Molecular tori in Seyfert galaxies - Feeding the monster and hiding it

Cited by 555 publications

References 0 publications

Reflection in Seyfert galaxies and the unified model of AGN

Reflection in Seyfert galaxies and the unified model of AGN

A new analysis of the nucleus of NGC 1068 with MIDI observations

Dust tori in radio galaxies

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