Abstract
Recent high angular resolution observations resolved for the first time the mid-infrared (MIR) structure of nearby active galactic nuclei (AGN). Surprisingly, they revealed that a major ...fraction of their MIR emission comes from the polar regions. This is at odds with the expectation based on AGN unification, which postulates a dusty torus in the equatorial region. The nearby, archetypical AGN in the Circinus galaxy offers one of the best opportunities to study the MIR emission in greater detail. New, high-quality MIR images obtained with the upgraded VISIR instrument at the Very Large Telescope show that the previously detected bar-like structure extends up to at least 40 pc on both sides of the nucleus along the edges of the ionization cone. Motivated by observations across a wide wavelength range and on different spatial scales, we propose a phenomenological dust emission model for the AGN in the Circinus galaxy consisting of a compact dusty disc and a large-scale dusty cone shell, illuminated by a tilted accretion disc with an anisotropic emission pattern. Undertaking detailed radiative transfer simulations, we demonstrate that such a model is able to explain the peculiar MIR morphology and account for the entire IR spectral energy distribution. Our results call for caution when attributing dust emission of unresolved sources entirely to the torus and warrant further investigation of the MIR emission in the polar regions of the AGN.
We present new interferometric data obtained with mid-infrared interferometric instrument (MIDI) for the type II Seyfert galaxy NGC 1068, with an extensive coverage of 16 uv points. These ...observations resolve the nuclear mid-infrared emission from NGC 1068 in unprecedented detail with a maximum resolution of 7 mas. For the first time, sufficient uv points have been obtained, allowing us to generate an image of the source using maximum entropy image reconstruction. The features of the image are similar to those obtained by modelling. We find that the mid-infrared emission can be represented by two components, each with a Gaussian brightness distribution. The first, identified as the inner funnel of the obscuring torus, is hot (∼800 K), 1.35 parsec long and 0.45 parsec thick in full width at half-maximum (FWHM) at a PA =−42° (from north to east). It has an absorption profile different than standard interstellar dust and with evidence for clumpiness. The second component is 3 × 4 pc in FWHM with T=∼300 K, and we identify it with the cooler body of the torus. The compact component is tilted by ∼45° with respect to the radio jet and has similar size and orientation to the observed water maser distribution. We show how the dust distribution relates to other observables within a few parsec of the core of the galaxy, such as the nuclear masers, the radio jet and the ionization cone. We compare our findings to a similar study of the Circinus galaxy and other relevant studies. Our findings shed new light on the relation between the different parsec-scale components in NGC 1068 and the obscuring torus.
Context. With infrared interferometry it is possible to resolve the nuclear dust distributions that are commonly associated with the dusty torus in active galactic nuclei (AGN). The Circinus galaxy ...hosts the closest Seyfert 2 nucleus and previous interferometric observations have shown that its nuclear dust emission is particularly well resolved. Aims. The aim of the present interferometric investigation is to better constrain the dust morphology in this active nucleus. Methods. To this end, extensive new observations were carried out with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer, leading to a total of 152 correlated flux spectra and differential phases between 8 and 13 μm. To interpret this data, we used a model consisting of black-body emitters with a Gaussian brightness distribution and with dust extinction. Results. The direct analysis of the data and the modelling confirm that the emission is distributed in two distinct components: a disk-like emission component with a size (FWHM) of ~0.2 × 1.1 pc and an extended component with a size of ~0.8 × 1.9 pc. The disk-like component is elongated along PA ~ 46° and oriented perpendicular to the ionisation cone and outflow. The extended component is responsible for 80% of the mid-infrared emission. It is elongated along PA ~ 107°, which is roughly perpendicular to the disk component and thus in polar direction. It is interpreted as emission from the inner funnel of an extended dust distribution and shows a strong increase in the extinction towards the south-east. We find both emission components to be consistent with dust at T ~ 300 K, that is we find no evidence of an increase in the temperature of the dust towards the centre. From this we infer that most of the near-infrared emission probably comes from parsec scales as well. We further argue that the disk component alone is not sufficient to provide the necessary obscuration and collimation of the ionising radiation and outflow. The material responsible for this must instead be located on scales of ~1 pc, surrounding the disk. We associate this material with the dusty torus. Conclusions. The clear separation of the dust emission into a disk-like emitter and a polar elongated source will require an adaptation of our current understanding of the dust emission in AGN. The lack of any evidence of an increase in the dust temperature towards the centre poses a challenge for the picture of a centrally heated dust distribution.
Resolving the Hot Dust Disk of ESO323-G77 Leftley, James H.; Tristram, Konrad R. W.; Hönig, Sebastian F. ...
The Astrophysical journal,
05/2021, Letnik:
912, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Infrared interferometry has led to a paradigm shift in our understanding of the dusty structure in the central parsecs of active galactic nuclei (AGNs). The dust is now thought to comprise a ...hot (∼1000 K) equatorial disk, some of which is blown into a cooler (∼300 K) polar dusty wind by radiation pressure. In this paper, we utilize the new near-IR interferometer GRAVITY on the Very Large Telescope Interferometer (VLTI) to study a Type 1.2 AGNs hosted in the nearby Seyfert galaxy ESO 323-G77. By modeling the squared visibility and closure phase, we find that the hot dust is equatorially extended, consistent with the idea of a disk, and shows signs of asymmetry in the same direction. Furthermore, the data is fully consistent with the hot dust size determined by
K
-band reverberation mapping as well as the predicted size from a CAT3D-WIND model created in previous work using the spectral energy distribution of ESO 323-G77 and observations in the mid-IR from VLTI/MID-infrared Interferometric instrument).
Abstract
Infrared interferometry of Seyfert galaxies has revealed that their warm (300–400 K) dust emission originates primarily from polar regions instead of from an equatorial dust torus as ...predicted by the classic AGN unification scheme. We present new data for the type 1.2 object ESO 323-G77 obtained with the MID-infrared interferometric Instrument and a new detailed morphological study of its warm dust. The partially resolved emission on scales between 5 and 50 mas (1.6–16 pc) is decomposed into a resolved and an unresolved source. Approximately 65% of the correlated flux between 8 and 13
μ
m is unresolved at all available baseline lengths. The remaining 35% is partially resolved and shows angular structure. From geometric modeling, we find that the emission is elongated along a position angle of 155° ± 14° with an axis ratio (major/minor) of 2.9 ± 0.3. Because the system axis is oriented in the position angle 174° ± 2°, we conclude that the dust emission of this object is also polar extended. A
CAT3D-WIND
radiative transfer model of a dusty disk and a dusty wind with a half opening angle of 30° can reproduce both the interferometric data and the SED, while a classical torus model is unable to fit the interferometric data. We interpret this as further evidence that a polar dust component is required even for low-inclination type 1 sources.
Abstract
Infrared interferometry of the local active galactic nucleus (AGN) has revealed a warm (∼300–400 K) polar dust structure that cannot be trivially explained by the putative dust torus of the ...unified model. This led to the development of the disk+wind scenario which comprises a hot (∼1000 K) compact equatorial dust disk and a polar dust wind. This wind is assumed to be driven by radiation pressure and, therefore, we would expect that long-term variation in radiation pressure would influence the dust distribution. In this paper we attempt to quantify if and how the dust distribution changes with radiation pressure. We analyze so far unpublished Very Large Telescope Interferometer (VLTI)/MID-infrared Interferometer (MIDI) data on 8 AGN and use previous results on 25 more to create a sample of 33 AGN. This sample comprises all AGN successfully observed with VLTI/MIDI. For each AGN, we calculate the Eddington ratio, using the intrinsic 2–10 keV X-ray luminosity and black hole mass, and compare this to the resolved dust emission fraction as seen by MIDI. We tentatively conclude that there is more dust in the wind at higher Eddington ratios, at least in type 2 AGN where such an effect is expected to be more easily visible.
Abstract
The nuclear region of Type 1 active galactic nuclei (AGNs) has only been partially resolved so far in the near-infrared (IR), where we expect to see the dust sublimation region and the ...nucleus directly without obscuration. Here, we present the near-IR interferometric observation of the brightest Type 1 AGN NGC 4151 at long baselines of ∼250 m using the CHARA Array, reaching structures at hundred microarcsecond scales. The squared visibilities decrease down to as low as ∼0.25, definitely showing that the structure is resolved. Furthermore, combining with the previous visibility measurements at shorter baselines but at different position angles, we show that the structure is elongated
perpendicular
to the polar axis of the nucleus, as defined by optical polarization and a linear radio jet. A thin-ring fit gives a minor/major axis ratio of ∼0.7 at a radius ∼0.5 mas (∼0.03 pc). This is consistent with the case where the sublimating dust grains are distributed preferentially in the equatorial plane in a ring-like geometry, viewed at an inclination angle of ∼40°. The recent mid-IR interferometric finding of polar-elongated geometry at a pc scale, together with a larger-scale polar outflow as spectrally resolved by the Hubble Space Telescope, would generally suggest a dusty, conical and hollow outflow being launched, presumably in the dust sublimation region. This might potentially lead to a polar-elongated morphology in the near-IR, as opposed to the results here. We discuss a possible scenario where an episodic, one-off anisotropic acceleration formed a polar-fast and equatorially slow velocity distribution, having led to an effectively flaring geometry as we observe.
Active galaxies contain a supermassive black hole at their center that grows by accreting matter from the surrounding galaxy. The accretion process in about the central 10 parsecs has not been ...directly resolved in previous observations because of the small apparent angular sizes involved. We observed the active nucleus of the Circinus Galaxy using submillimeter interferometry. A dense inflow of molecular gas was evident on subparsec scales. We calculated that less than 3% of this inflow is accreted by the black hole, with the rest being ejected by multiphase outflows, providing feedback to the host galaxy. Our observations also reveal a dense gas disk surrounding the inflow that is gravitationally unstable, which drives the accretion into about the central 1 parsec.
Editor’s summary
Most galaxies contain a supermassive black hole at their center. When gas falls toward the black hole, it heats up and emits radiation and can be observed as an active galactic nucleus. However, it is not known how gas is delivered from the wider galaxy to the inner region around the black hole. Izumi
et al
. combined submillimeter observations of several gas tracers in the center of the Circinus Galaxy, a nearby active galactic nucleus. By comparing the kinematics of molecular, atomic, and ionized gas, they were able to identify an inflow of dense molecular gas in the central parsec, feeding the black hole. —Keith T. Smith
Observations of an active galaxy show an inflow of dense molecular gas into the inner parsec around the supermassive black hole.
Aims. To test the dust torus model for active galactic nuclei directly, we study the extent and morphology of the nuclear dust distribution in the Circinus galaxy using high resolution ...interferometric observations in the mid-infrared. Methods. Observations were obtained with the MIDI instrument at the Very Large Telescope Interferometer. The 21 visibility points recorded are dispersed with a spectral resolution of \lambda/\delta\lambda\approx30 in the wavelength range from 8 to 13 \mu{\rm m}. To interpret the data we used a stepwise approach of modelling with increasing complexity. The final model consists of two black body Gaussian distributions with dust extinction. Results. We find that the dust distribution in the nucleus of Circinus can be explained by two components, a dense and warm disk-like component of 0.4 pc size and a slightly cooler, geometrically thick torus component with a size of 2.0 pc. The disk component is oriented perpendicular to the ionisation cone and outflow and seems to show the silicate feature at 10 \mu{\rm m} in emission. It coincides with a nuclear maser disk in orientation and size. From the energy needed to heat the dust, we infer a luminosity of the accretion disk of L_{{\rm acc}} = 10 super(10) {L}_{\odot}, which corresponds to 20% of the Eddington luminosity of the nuclear black hole. We find that the interferometric data are inconsistent with a simple, smooth and axisymmetric dust emission. The irregular behaviour of the visibilities and the shallow decrease of the dust temperature with radius provide strong evidence for a clumpy or filamentary dust structure. We see no evidence for dust reprocessing, as the silicate absorption profile is consistent with that of standard galactic dust. We argue that the collimation of the ionising radiation must originate in the geometrically thick torus component. Conclusions. Based on a great leap forward in the quality and quantity of interferometric data, our findings confirm the presence of a geometrically thick, torus-like dust distribution in the nucleus of Circinus, as required in unified schemes of Seyfert galaxies. Several aspects of our data require that this torus is irregular, or "clumpy".
The near-IR emission in Type 1 active galactic nuclei (AGNs) is thought to be dominated by the thermal radiation from dust grains that are heated by the central engine in the UV/optical and are ...almost at the sublimation temperature. A brightening of the central source can thus further sublimate the innermost dust, leading to an increase in the radius of the near-IR emitting region. Such changes in radius have been indirectly probed by the measurements of the changes in the time lag between the near-IR and UV/optical light variation. Here we report direct evidence for such a receding sublimation region through the near-IR interferometry of the brightest Type 1 AGN in NGC 4151. The increase in radius follows a significant brightening of the central engine with a delay of at least a few years, which is thus the implied destruction timescale of the innermost dust distribution. Compiling historic flux variations and radius measurements, we also infer the reformation timescale for the inner dust distribution to be several years in this galactic nucleus. More specifically and quantitatively, we find that the radius at a given time seems to be correlated with a long-term average of the flux over the previous several (~6) years, instead of the instantaneous flux. Finally, we also report measurements of three more Type 1 AGNs newly observed with the Keck interferometer, as well as the second epoch measurements for three other AGNs.
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