The narrow Fe K$\alpha$ line and the molecular torus in active galactic
  nuclei - an IR/X-ray view
  The narrow component of the iron K$\alpha$ is an almost ubiquitous feature in
the X-ray spectra of active galactic nuclei (AGN) and is believed to originate
in neutral material, possibly located in the molecular torus. This would imply
a tight connection between the Fe K$\alpha$ equivalent width (EW) and the
physical properties of the torus. In a recent work we have shown that the
decrease of the covering factor of the torus with the luminosity, as expected
by luminosity-dependent unification models, would be able to explain the
decrease of Fe K$\alpha$ EW with the luminosity (i.e., the X-ray Baldwin
effect). Recent developments in the study of the mid-IR (MIR) spectrum of AGN
allow important parameters of the torus to be deduced, such as its covering
factor ($f_{\rm\,obs}$) and equatorial column density ($N_{\rm\,H}^{\rm\,T}$),
by applying clumpy torus models. Using XMM-Newton/EPIC observations of a sample
of 24 type-I AGN, we investigate the relation between the physical parameters
of the torus obtained by recent MIR works and the properties of the Fe
K$\alpha$ line. We correct the values of the Fe K$\alpha$ EW by taking the
inclination angle, the photon index, the equatorial column density, and
half-opening angle of the torus into account using a physical torus model of
X-ray reprocessed radiation. We find that the relation between Fe K$\alpha$ EW
and $f_{\rm\,obs}$ shows a slope that is consistent with the expected value,
albeit with a low statistical significance. A trend that is consistent with the
theoretical prediction is also found when comparing the Fe K$\alpha$ EW to
$N_{\rm\,H}^{\rm\,T}$. Our work seems to confirm that the bulk of the narrow Fe
K$\alpha$ line is produced by the same material responsible for the MIR
emission.
