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20 April 2024 |
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Dust in the polar region as a major contributor to the IR emission of AGN | | Sebastian F. Hoenig
; Makoto Kishimoto
; Konrad R. W. Tristram
; M. Almudena Prieto
; Poshak Gandhi
; Daniel Asmus
; Robert Antonucci
; Leonard Burtscher
; Wolfgang J. Duschl
; Gerd Weigelt
; | | Date: |
18 Jun 2013 | | Abstract: | (abridged) It is generally assumed that the distribution of dust 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 sub-arcsecond-scale IR emission and gives rise to
orientation-dependent obscuration. 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 PA -52 deg, closely aligned with the polar axis (PA -45 deg). We
determine half-light radii along the major and minor axes at 12.5 {mu}m of
(4.23 +/- 0.63) pc x (1.42 +/- 0.21) pc, which corresponds to
intrinsically-scaled sizes of (69.4 +/- 10.8) rin x (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
{mu}m emission associated with the polar-elongated component. These
observations are difficult to reconcile with the standard interpretation that
most of the parsec-scale mid-IR emission in AGN originates from the torus and
challenges the justification of using simple torus models to model the
broad-band IR emission. It is quite likely that the hot-dust emission in NGC
3783 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 {mu}m and 20 {mu}m bumps seen in the high-angular resolution spectral
energy distribution (SED). We conclude that these observations support a
scenario where the majority of the mid-IR emission in Seyfert AGN originates
from a dusty wind in the polar region of the AGN. | | Source: | arXiv, 1306.4312 | | Services: | Forum | Review | PDF | Favorites | |
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