Probing the nature and origin of dust in the reddened quasar IC 4329A
  with global modelling from X-ray to infrared
  Cosmic dust is a key tracer of structure formation and evolution in the
universe. In active galactic nuclei (AGN) the origin and role of dust are
uncertain. Here, we have studied dust in the X-ray bright and reddened type-1
quasar IC 4329A, which exhibits an ionised AGN wind. We incorporated
high-resolution X-ray and mid-IR spectroscopy, combined with broad-band
continuum modelling, to investigate the properties of dust in this AGN. We used
new Chandra HETGS observations taken in June 2017, as well as archival data
from XMM-Newton, Swift, HST, Spitzer, IRAS, and Herschel for our
IR-optical-UV-X-ray modelling. Two distinct components of dust in IC 4329A are
found. One component is in the interstellar medium (ISM) of the host galaxy,
and the other is a nuclear component in the AGN torus and its associated wind.
The emitting dust in the torus is evident in mid-IR emission (9.7 and 18 micron
features), while dust in the wind is present through both reddening and X-ray
absorption (O, Si, and Fe edge features). The gas depletion factors into dust
for O, Si, and Fe are measured. We derive an intrinsic reddening E(B-V) ~ 1.0,
which is most consistent with a grey (flat) extinction law. The AGN wind
consists of three ionisation components. From analysis of long-term changes in
the wind, we determine limits on the location of the wind components. The two
lowest ionisation components are likely carriers of dust from the AGN torus. We
find that the dust in the nuclear component of IC 4329A is different from dust
in the Milky Way. The dust grains in the AGN torus and wind are likely larger
than the standard Galactic dust, and are in a porous composite form (containing
amorphous silicate with iron and oxygen). This can be a consequence of grain
coagulation in the dense nuclear environment of the AGN.
