ABSTRACT We present results from a 15 month campaign of high-cadence (∼3 days) mid-infrared Spitzer and optical (B and V) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of ...determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). We find that the 3.6 and 4.5 m flux variations lag behind those of the optical continuum by days and days, respectively. We report a cross-correlation time lag between the 4.5 and 3.6 m flux of days. The lags indicate that the dust emitting at 3.6 and 4.5 m is located at a distance light-month ( ) from the source of the AGN UV-optical continuum. The reverberation radii are consistent with the inferred lower limit to the sublimation radius for pure graphite grains at 1800 K, but smaller by a factor of ∼2 than the corresponding lower limit for silicate grains; this is similar to what has been found for near-infrared (K-band) lags in other AGNs. The 3.6 and 4.5 m reverberation radii fall above the K-band size-luminosity relationship by factors and , respectively, while the 4.5 m reverberation radius is only 27% larger than the 3.6 m radius. This is broadly consistent with clumpy torus models, in which individual optically thick clouds emit strongly over a broad wavelength range.
We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the GRAVITY instrument on the European Southern Observatory Very Large Telescope Interferometer. The ...extensive baseline coverage from 5 to 60 M λ allowed us to reconstruct a continuum image of the nucleus with an unrivaled 0.2 pc resolution in the K -band. We find a thin ring-like structure of emission with a radius r = 0.24 ± 0.03 pc, inclination i = 70 ± 5°, position angle PA = −50 ± 4°, and h / r < 0.14, which we associate with the dust sublimation region. The observed morphology is inconsistent with the expected signatures of a geometrically and optically thick torus. Instead, the infrared emission shows a striking resemblance to the 22 GHz maser disc, which suggests they share a common region of origin. The near-infrared spectral energy distribution indicates a bolometric luminosity of (0.4–4.7) × 10 45 erg s −1 , behind a large A K ≈ 5.5 ( A V ≈ 90) screen of extinction that also appears to contribute significantly to obscuring the broad line region.
Infrared (IR) interferometry has made widely recognised contributions to the way we look at the dusty environment of supermassive black holes on parsec scales. It finally provided direct evidence for ...orientation-dependent unification of active galaxies, however it also showed that the classical “torus” picture is oversimplified. New scientific opportunities for AGN have been suggested, and will soon be carried out, focusing on the dynamical aspects of spectrally and spatially resolved interferometry, as well as the potential to employ interferometry for cosmology. This will open interferometry to new scientific communities.
Infrared (IR) interferometry has made widely recognised contributions to the way we look at the dusty environment of supermassive black holes on parsec scales. It finally provided direct evidence for ...orientation-dependent unification of active galaxies, however it also showed that the classical “torus” picture is oversimplified. New scientific opportunities for AGN have been suggested, and will soon be carried out, focusing on the dynamical aspects of spectrally and spatially resolved interferometry, as well as the potential to employ interferometry for cosmology. This will open interferometry to new scientific communities.
Spatially-resolved velocity maps at high resolutions of 1-10 pc are becoming available for many nearby AGNs in both optical/infrared atomic emission lines and sub-mm molecular lines. For the former, ...it has been known that a linear relationship appears to exist between the velocity of the ionized gas clouds and the distance from the nucleus in the inner ~100 pc region, where these clouds are outflowing. Here we demonstrate that, in such a case, we can actually derive the three-dimensional (3D) geometrical distribution of the clouds directly from the velocity map. Revisiting such a velocity map taken by HST for the prototypical Type 2 AGN NGC1068, we implement the visualization of the 3D distribution derived from the map, and show that this inner narrow-line region has indeed a hollow-cone structure, consistent with previous modeling results. Quite possibly, this is the outer extended part of the polar elongated dusty material seen in the recent mid-IR interferometry at pc scale. Conversely, the latter small-scale geometry is inferred to have a hollow-cone outflowing structure as the inward extension of the derived 3D distribution above. The AGN obscuring "torus" is argued to be the inner optically thick part of this hollow-cone outflow, and its shadowed side would probably be associated with the molecular outflow seen in certain sub-mm lines. We discuss the nature of the linear velocity field, which could be from an episodic acceleration that had occurred ~10^5 years ago.
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