Radiation feedback on dusty clouds during Seyfert activity
  We investigate the evolution of dusty gas clouds falling into the centre of
an active Seyfert nucleus. Two-dimensional high-resolution radiation
hydrodynamics simulations are performed to study the fate of single clouds and
the interaction between two clouds approaching the Active Galactic Nucleus. We
find three distinct phases of the evolution of the cloud: (i) formation of a
lenticular shape with dense inner rim caused by the interaction of gravity and
radiation pressure (the lense phase), (ii) formation of a clumpy sickle-shaped
structure as the result of a converging flow (the clumpy sickle phase) and
(iii) a filamentary phase caused by a rapidly varying optical depth along the
sickle. Depending on the column density of the cloud, it will either be pushed
outwards or its central (highest column density) parts move inwards, while
there is always some material pushed outwards by radiation pressure effects.
The general dynamical evolution of the cloud can approximately be described by
a simple analytical model.
