Bibcode
Hönig, S. F.; Kishimoto, M.; Antonucci, R.; Marconi, A.; Prieto, M. A.; Tristram, K.; Weigelt, G.
Referencia bibliográfica
The Astrophysical Journal, Volume 755, Issue 2, article id. 149 (2012).
Advertised on:
8
2012
Revista
Número de citas
134
Número de citas referidas
123
Descripción
Advancements in infrared (IR) interferometry open up the possibility to
spatially resolve active galactic nuclei (AGNs) on the parsec-scale
level and study the circumnuclear dust distribution, commonly referred
to as the "dust torus," that is held responsible for the type 1/type 2
dichotomy of AGNs. We used the mid-IR beam combiner MIDI together with
the 8 m telescopes at the Very Large Telescope Interferometer to observe
the nucleus of the Seyfert 2 galaxy NGC 424, achieving an almost
complete coverage of the uv-plane accessible by the available telescope
configurations. We detect extended mid-IR emission with a relatively
baseline- and model-independent mid-IR half-light radius of (2.0
± 0.2) pc × (1.5 ± 0.3) pc (averaged over the 8-13
μm wavelength range). The extended mid-IR source shows an increasing
size with wavelength. These properties are in agreement with the idea of
dust heated in thermal equilibrium with the AGN. The orientation of the
major axis in position angle ~ - 27° is closely aligned with
the system axis as set by optical polarization observations. Torus
models typically favor extension along the mid-plane at mid-IR
wavelengths instead. Therefore, we conclude that the majority of the
parsec-scale mid-IR emission (gsim60%) in this type 2 AGN originates
from optically thin dust in the polar region of the AGN, a scenario
consistent with the near- to far-IR spectral energy distribution. We
suggest that a radiatively driven dusty wind, possibly launched in a
puffed-up region of the inner hot part of the torus, is responsible for
the polar dust. In this picture, the torus dominates the near-IR
emission up to about 5 μm, while the polar dust is the main
contributor to the mid-IR flux. Our results of NGC 424 are consistent
with recent observations of the AGN in the Circinus galaxy and resemble
large-scale characteristics of other objects. If our results reflect a
general property of the AGN population, the current paradigm for
interpreting and modeling the IR emission of AGNs has to be revised.
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Centros de Galaxias a Escalas de Parsecs y Técnicas de Alta Resolución Espacial
Proyecto enfocado al estudio en el IR del núcleo de las galaxias más cercanas con resoluciones espaciales en el rango de 1 a 10 pc. Estas resoluciones espaciales, accesibles con los grandes telescopios de tierra usando técnicas frontera de observación, son por primera vez comparables a las que se obtienen rutinariamente con HST en el óptico y VLBI
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