DUST IN THE POLAR REGION AS A MAJOR CONTRIBUTOR TO THE INFRARED EMISSION OF ACTIVE GALACTIC NUCLEI

By S. Hoenig, M. Kishimoto, K. Tristram, M. Prieto, Poshak Gandhi, D. Asmus, R. Antonucci, L. Burtscher, Wolfgang J. Duschl, Gerd Weigelt Ucsb and 8 more. 2013

134 citations recorded by the source corpus.

Dust around active galactic nuclei (AGNs) is distributed over a wide range of spatial scales and can be observed in the infrared (IR). It is generally assumed that the distribution on parsec scales forms a geometrically and optically thick entity in the equatorial plane around the accretion disk and broad-line region—dubbed “dust torus”—that emits the bulk of the subarcsecond-scale IR emission and gives rise to orientation-dependent obscuration. However, recent IR interferometry studies with unprecedented position angle (P.A.) and baseline coverage on these small scales in two obscured (type 2) AGNs have revealed that the majority of the mid-IR emission in these objects is elongated in the polar direction. These observations are difficult to reconcile with the standard interpretation that most of the parsec-scale mid-IR emission in AGNs originate from the torus and challenges the justification of using simple torus models to model the broadband IR emission. Here, we report detailed interferometry observations of the unobscured (type 1) AGN in NGC 3783 that allow us to constrain the size, elongation, and direction of the mid-IR emission with high accuracy. The mid-IR emission is characterized by a strong elongation toward position angle P.A. −52°, closely aligned with the polar axis (P.A. −45°). We determine half-light radii along the major and minor axes at 12.5 μm of (20.0 ± 3.0) mas × (6.7 ± 1.0) mas or (4.23 ± 0.63) pc × (1.42 ± 0.21) pc, which corresponds to intrinsically scaled sizes of (69.4 ± 10.8) rin × (23.3 ± 3.5) rin for the inner dust radius of rin = 0.061 pc as inferred from near-IR reverberation mapping. This implies an axis ratio of 3:1, with about 60%–90% of the 8–13 μm emission associated with the polar-elongated component. It is quite likely that the hot-dust emission as recently resolved by near-IR interferometry is misaligned with the mid-IR emitting source, which also finds a correspondence in the two distinct 3–5 μm and 20 μm bumps seen in the high angular resolution spectral energy distribution (SED). Based on this SED, we determine covering factors for the hot and warm dust components of and , respectively. We conclude that these observations support a scenario where the majority of the mid-IR emission in Seyfert AGNs originate from a dusty wind in the polar region of the AGN.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/df492bbaf933a3053731a554c12cd63efb1c6bf1

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In Astronomy and Astrophysics

1. H. Netzer
2. M. Kishimoto
3. S. Hönig
4. Wolfgang J. Duschl
5. D. Asmus
6. Poshak Gandhi
7. S. Hönig
8. A. Smette

In Instrumentation

1. Wolfgang J. Duschl
2. D. Asmus
3. H. Netzer
4. Garching
5. Heidelberg
6. Poshak Gandhi
7. S. Hönig
8. L. Observatory

Citations in the corpus

• Revisiting the Unified Model of Active Galactic Nuclei (2015, methodology): “This geometry was interpreted by Hönig et al. (2013) as a combination of an inner small torus, where the 24 Netzer dust is very hot, and a dusty polar outflow which, because of its distance, contains cooler dust.”
• The subarcsecond mid-infrared view of local active galactic nuclei – I. The N- and Q-band imaging atlas (2013, background): “It has been well documented that many QSOs and Sy1 galaxies exhibit what is called the 3- 5 µm bump (e.g., Edelson & Malkan 1986; Kishimoto et al. 2011; Mor & Netzer 2012; Hönig et al. 2013).”
• A diversity of dusty AGN tori - Data release for the VLTI/MIDI AGN Large Program and first results for 23 galaxies (2013, methodology): “…(u, v) coverages have been achieved for two fainter sources, the Seyfert 2 galaxy NGC 424 and the Seyfert 1.5 galaxy NGC 3783, and their extended components have been found to be slightly elongated with axis ratios of 1.3 in NGC 424 (Hönig et al., 2012) and 1.5 in NGC 3783 (Hönig et al., 2013).”
• The subarcsecond mid-infrared view of local active galactic nuclei – II. The mid-infrared–X-ray correlation (2015, background): “Second, as the most recent interferometric results indicate, the majority of MIR emission is actually produced in the polar outflow region rather than in a canonical torus (Hönig et al. 2012, 2013; Tristram et al. 2014).”
• The dusty torus in the Circinus galaxy: a dense disk and the torus funnel (2013, background): “In fact, there is mounting evidence that this is a common characteristic of Seyfert galaxies: also in NGC 1068, NGC 424 and NGC 3783 the majority of the emission is extended in polar direction (Poncelet et al. 2007; Raban et al. 2008; Hönig et al. 2012, 2013).”