Max Planck Institute for Astronomy - Annual Report 2005

60 ly
Fig. II.5.3: Temperature distribution in the model of a homogeneous
torus. In the innermost region more than 1000 Kelvin are
reached (orange). Towards the outside the temperature decreases
continuously to about 100 Kelvin (dark red).
Fig. II.5.4: These mid-infrared images of the dust tori are predicted
by continuous models. The upper panel shows the torus
of a Seyfert 1 galaxy at wavelengths of 5, 12, and 30 �m. The
lower panel shows the corresponding appearance of a Seyfert 2
galaxy at the same wavelengths. At short wavelengths only the
inner, hot channel of the torus is glowing.
Seyfert 1
5 �m
Seyfert 2
5 �m
10 pc
Seyfert 1
12 �m
Seyfert 2
12 �m
II.5. Dust Tori in Active Galactic Nuclei 33
complex gas and dust distribution by the accretion disk
and the pathway for the escape of the resulting infrared
radiation would have to be calculated each time. Such a
model would need millions of spatial cells and thousands
of time steps in the computer – far more than present-day
computers can manage. We therefore approach the modeling
in three steps of increasing complexity.
In the first step, we distribute gas and dust in an effective
potential determined by the mass of the black hole
and the central star cluster (mass, velocity distribution,
rotation). In this way we try to reproduce the properties
of a typical Seyfert galaxy. By illuminating this stationary
and continuous dust distribution with the radiation of
a hot accretion disk, one not only obtains the temperature
distribution of the dust torus (Fig. II.5.3), but one can
also derive images of the radiation escaping at various
wavelengths. Figure II.5.4 shows the expected images of
the torus for Seyfert 1 (upper panel) and Seyfert 2 galaxies.
Notice that at shorter wavelengths (λ � 5 �m) only
the hot inner edge of the torus is discernible, while at
longer wavelengths larger and larger regions of the torus
are glowing. This is due to the decreasing temperature at
increasing distances to the black hole.
In the first step, we distribute gas and dust in an effective
potential determined by the mass of the black hole
and the central star cluster (mass, velocity distribution, rotation).
In this way we try to reproduce the properties of a
typical Seyfert galaxy. By illuminating this stationary and
continuous dust distribution with the radiation of a hot ac-
Seyfert 1
30 �m
Seyfert 2
30 �m