Bibcode
Hönig, S. F.; Kishimoto, M.; Tristram, K. R. W.; Prieto, M. A.; Gandhi, P.; Asmus, D.; Antonucci, R.; Burtscher, L.; Duschl, W. J.; Weigelt, G.
Referencia bibliográfica
The Astrophysical Journal, Volume 771, Issue 2, article id. 87, 14 pp. (2013).
Fecha de publicación:
7
2013
Revista
Número de citas
194
Número de citas referidas
180
Descripción
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) r
in × (23.3 ± 3.5) r in for the inner
dust radius of r in = 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 C_{hot} =
0.42^{+0.42}_{-0.21} and C_{warm} = 0.92^{+0.92}_{-0.46}, 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.
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