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Register a new userThe Galaxy Activity, Torus and Outflow Survey (GATOS): II. Torus and polar dust emission in nearby Seyfert galaxies
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Almudena Alonso-Herrero
Publication date
2021
fields
Physics
and research's language is
English
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We compare mid-IR and ALMA far-IR images of 12 nearby Seyferts selected from GATOS. The mid-IR unresolved emission contributes more than 60% of the nuclear emission in most galaxies. By contrast, the ALMA 870micron continuum emission is mostly resolved and typically along the torus equatorial direction (Paper I, Garcia-Burillo et al. 2021). The Eddington ratios and nuclear hydrogen column densities NH of half the sample are favorable to launching polar and/or equatorial dusty winds, according to simulations. Six show mid-IR extended emission in the polar direction as traced by the NLR and perpendicular to the ALMA emission. In a few, the nuclear NH might be too high to uplift large quantities of dusty material along the polar direction. Five galaxies have low NH and/or Eddington ratios and thus polar dusty winds are not likely. We generate new CAT3D-WIND disk-wind model images. At low wind-to-disk cloud ratios the far-IR model images have disk- and ring-like morphologies. The X-shape associated with dusty winds is seen better in the far-IR at intermediate-high inclinations for the extended-wind configurations. In most models, the mid-IR emission comes from the inner part of the disk/cone. Extended bi-conical and one-sided polar mid-IR emission is seen in extended-wind configurations and high wind-to-disk cloud ratios. When convolved to our resolution, the model images reproduce qualitative aspects of the observed morphologies. Low-intermediate wind-to-disk ratios are required to account for the large fractions of unresolved mid-IR emission. This work and Paper I provide observational support for the torus+wind scenario. The wind component is more relevant at high Eddington ratios and/or AGN luminosities, and polar dust emission is predicted at NH of up to $10^{24}$cm$^{-2}$. The torus/disk component, on the other hand, prevails at low luminosities and/or Eddington ratios. (Abridged)
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We present the first results of the Galaxy Activity, Torus and Outflow Survey (GATOS), a project aimed at understanding the properties of the dusty molecular tori and their connection to the host galaxy in nearby Seyfert galaxies. Our project expands the range of AGN luminosities and Eddington ratios covered by previous surveys of Seyferts conducted by ALMA and allows us to study the gas feeding and feedback cycle in a combined sample of 19 Seyferts. We used ALMA to obtain new images of the emission of molecular gas and dust using the CO(3-2) and HCO+(4-3) lines as well as their underlying continuum emission at 870 microns with high spatial resolutions (0.1 ~ 7 - 13 pc) in the CND of 10 nearby (D < 28 Mpc) Seyfert galaxies. Our new ALMA observations detect 870 micron continuum and CO line emission from spatially resolved disks located around the AGN in all the sources. The bulk of the continuum flux can be accounted for by thermal emission from dust in the majority of the targets. For most of the sources the disks show a preponderant orientation perpendicular to the AGN wind axes, as expected for dusty molecular tori. The median diameters and molecular gas masses of the tori are ~ 42 pc, and ~ 6 x 10**5 Msun, respectively. We find a positive correlation between the line-of-sight gas column densities responsible for the absorption of X-rays and the molecular gas column densities derived from CO towards the AGN in our sources. The radial distributions of molecular gas in the CND of our combined sample show signs of nuclear-scale molecular gas deficits. We also detect molecular outflows in the sources that show the most extreme nuclear-scale gas deficits in our sample. These observations find for the first time supporting evidence that the imprint of AGN feedback is more extreme in higher luminosity and/or higher Eddington ratio Seyfert galaxies.
We present the results of a dust reverberation survey for 17 nearby Seyfert 1 galaxies, which provides the largest homogeneous data collection for the radius of the innermost dust torus. A delayed response of the K-band light curve after the V-band light curve was found for all targets, and 49 measurements of lag times between the flux variation of the dust emission in the K band and that of the optical continuum emission in the V band were obtained. The lag times strongly correlated with the optical luminosity in the luminosity range of M_V=-16 to -22 mag, and the regression analysis was performed to obtain the correlation log $Delta t$ (days) = -2.11 -0.2 M_V assuming $Delta t propto L^{0.5}$, which was theoretically expected. We discuss the possible origins of the intrinsic scatter of the dust lag-luminosity correlation, which was estimated to be about 0.13 dex, and we find that the difference of internal extinction and delayed response of changes in lag times to the flux variations could have partly contributed to intrinsic scatter. However, we could not detect any systematic change of the correlation with the subclass of the Seyfert type or the Eddington ratio. Finally, we compare the dust reverberation radius with the near-infrared interferometric radius of the dust torus and the reverberation radius of broad Balmer emission lines. The interferometric radius in the K band was found to be systematically larger than the dust reverberation radius in the same band by about a factor of two, which could be interpreted by the difference between the flux-weighted radius and the response-weighted radius of the innermost dust torus. The reverberation radius of the broad Balmer emission lines was found to be systematically smaller than the dust reverberation radius by about a factor of 4-5, which strongly supports the unified scheme of the Seyfert type of active galactic nuclei. (Abridged)
Optical and near-mid-infrared reverberation mapping data obtained at Universit{a}tssternwarte Bochum in Chile and with the Spitzer Space Telescope allow us to explore the geometry of both the H$alpha$ BLR and the dust torus for the nearby Seyfert 1 galaxy WPVS,48. On average, the H$alpha$ variations lag the blue AGN continuum by about 18 days, while the dust emission variations lag by 70 days in the J+K and by 90 days in the L+M bands. The IR echoes are sharp, while the H$alpha$ echo is smeared. This together favours a bowl-shaped toroidal geometry where the dust sublimation radius is defined by a bowl surface, which is virtually aligned with a single iso-delay surface, thus leading to the sharp IR echoes. The BLR clouds, however, are located inside the bowl and spread over a range of iso-delay surfaces, leading to a smeared echo.
(Abridged) 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 well resolved. To better constrain the dust morphology in this active nucleus, extensive new observations were carried out with MIDI at the Very Large Telescope Interferometer. The emission is distributed in two distinct components: a disk-like emission component with a size of ~ 0.2 $times$ 1.1 pc and an extended component with a size of ~ 0.8 $times$ 1.9 pc. The disk-like component is elongated along PA ~ 46{deg} and oriented perpendicular to the ionisation cone and outflow. The extended component is elongated along PA ~ 107{deg}, 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 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. 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.
We studied the physical parameters of a sample comprising of all Spitzer/IRS public spectra of Seyfert galaxies in the mid-infrared (5.2-38$mu$m range) under the active galactic nuclei (AGN) unified model. We compare the observed spectra with $sim10^6$ CLUMPY model spectral energy distributions, which consider a torus composed of dusty clouds. We find a slight difference in the distribution of line-of-sight inclination angle, $i$, requiring larger angles for Seyfert 2 (Sy2) and a broader distribution for Seyfert 1 (Sy1). We found small differences in the torus angular width, $sigma$, indicating that Sy1 may host a slightly narrower torus than Sy2. The torus thickness, together with the bolometric luminosities derived, suggest a very compact torus up to $sim$6 pc from the central AGN. The number of clouds along the equatorial plane, $N$, as well the index of the radial profile, $q$, are nearly the same for both types. These results imply that the torus cloud distribution is nearly the same for type 1 and type 2 objects. The torus mass is almost the same for both types of activity, with values in the range of $M_{tor}sim$10$^{4}-$10$^{7}rm M_{odot}$. The main difference appears to be related to the clouds intrinsic properties: type 2 sources present higher optical depths $tau_V$. The results presented here reinforce the suggestion that the classification of a galaxy may depend also on the intrinsic properties of the torus clouds rather than simply on their inclination. This is in contradiction with the simple geometric idea of the unification model.
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