The innermost dusty structure in active galactic nuclei as probed by the Keck interferometer

Abstract

We are now exploring the inner region of type 1 active galactic nuclei (AGNs) with the Keck interferometer in the near-infrared. Adding to the four targets previously studied, we report measurements of the K-band (2.2 μm) visibilities for four more targets, namely AKN120, IC 4329A, Mrk6, and the radio-loud QSO 3C 273 at z = 0.158. The observed visibilities are quite high for all the targets, which we interpret as an indication of the partial resolution of the dust sublimation region. The effective ring radii derived from the observed visibilities scale approximately with L 1/2 , where L is the AGN luminosity. Comparing the radii with those from independent optical-infrared reverberation measurements, these data support our previous claim that the interferometric ring radius is either roughly equal to or slightly larger than the reverberation radius. We interpret the ratio of these two radii for a given L as an approximate probe of the radial distribution of the inner accreting material. We show tentative evidence that this inner radial structure might be closely related to the radio-loudness of the central engine. Finally, we re-observed the brightest Seyfert 1 galaxy NGC 4151. Its marginally higher visibility at a shorter projected baseline, compared to our previous measurements obtained one year before, further supports the partial resolution of the inner structure. We did not detect any significant change in the implied emission size when the K-band flux was brightened by a factor of 1.5 over a time interval of one year.

Blazar Sheath Illumination of the Outer Molecular Torus: A Resolution of the Seed Photon Problem for the Far-GeV Blazar Flares

“…Nenkova et al 2008;Elitzur, 2012;Netzer 2015) support the idea that the MT is clumpy (Krolik & Begelman 1988) and, furthermore, that the distribution of the dusty clumps is a gradually declining function of decreasing polar angle, allowing for some fraction of dusty clumps to lie at relatively small polar angles (e.g., García-González et al 2017;Khim & Yi 2017). The inner radius R d of the MT is set by dust sublimation due to the radiation of the accretion disk and has been measured by near-IR interferometry (e.g., Kishimoto et al 2011) and near IR reverberation mapping (e.g., Koshida et al 2014) of nearby Seyferts to have a size that for bright AGN (accretion disk luminosity L optical−U V ∼ 10 46 erg s −1 ) would be R d ∼ 1 pc (Nenkova et al 2008). …”

IC 751: A NEW CHANGING LOOK AGN DISCOVERED BYNUSTAR

“…Using a similar approach it is possible to put constraints on the location of the hot inner wall of the torus, which is also known to scale with the square-root of the luminosity (e.g., Suganuma et al 2006, Kishimoto et al 2011. Following Tristram & Schartmann (2011) (Fig.…”

Akari Observations of Dusty Tori of Active Galactic Nuclei

“…The hotter-dust component is associated with graphite located closer to the central engine, as graphite has a higher sublimation temperature than silicate. Interferometry and reverberation mapping observations show that the innermost size of dusty torus determined by sublimation of dust grain is smaller than a few parsecs (Suganuma et al, 2006;Kishimoto et al, 2011). For high-redshift quasars, observations with Infrared Space Observatory, AKARI, and Spitzer revealed the presence of hot dust, which indicates that the nuclear structures are already in place at high redshift.…”