Poster Presentation

Why is silicate feature of AGN polar dust so weak?

Author(s): Ryo Tazaki (Tohoku University) Kohei Ichikawa (Tohoku University)

Presenter: Ryo Tazaki (Tohoku university)

Recent mid-infrared interferometric observations have suggested that
the most of mid-infrared (MIR) emission of active galactic nuclei
(AGN) appears to emanate from polar regions high above the equatorial
plane, although their origin is still being debated. Interestingly,
these polar dust grains tend to show weak ~10 um silicate feature in
their spatially resolved spectra. We develop a simple toy model and
calculate the trajectory of dust grains above dust tori taking
radiation pressure from both AGN and the dust torus. As a result, we
show that larger grains are more readily blown out toward the polar
region because of inefficient gas drag and efficient radiation
pressure from the torus. In addition, highly accelerated small grains
suffer erosion, which also leads depletion of small grains at the
polar region. Since large grains are inefficient emitters of silicate
feature, the prevalence of large grains at polar region might explain
a lack of silicate feature in polar MIR emission.