X-ray signatures of the polar dusty gas in AGN
  Recent mid-infrared interferometry observations of nearby active galactic
nuclei (AGN) revealed that a significant part of the dust emission extends in
the polar direction, rather than the equatorial torus/disk direction as
expected by the traditional unification model. We study the X-ray signatures of
this polar dusty gas with ray-tracing simulations. Different from those from
the ionized gas, the scattered emission from the polar dusty gas produces
self-absorption and neutral-like fluorescence lines, which are potentially a
unique probe of the kinematics of the polar dusty gas. The anomalously small Fe
Ka/Si Ka ratios of type II AGN observed previously can be naturally explained
by the polar dusty gas, because the polar emission does not suffer from heavy
absorption by the dense equatorial gas. The observed Si Ka lines of the
Circinus galaxy and NGC 1068 show blue-shifts with respect to the systemic
velocities of the host galaxies, consistent with an outflowing scenario of the
Si Ka-emitting gas. The 2.5-3 keV image of the Circinus galaxy is elongated
along the polar direction, consistent with an origin of the polar gas. These
results show that the polar-gas-scattered X-ray emission of type II AGN is an
ideal objective for future X-ray missions, such as Athena.
