The dust sublimation radius as an outer envelope to the bulk of the
  narrow Fe Kalpha line emission in Type 1 AGN
  The Fe Kalpha emission line is the most ubiquitous feature in the X-ray
spectra of active galactic nuclei (AGN), but the origin of its narrow core
remains uncertain. Here, we investigate the connection between the sizes of the
Fe core emission regions and the measured sizes of the dusty tori in 13 local
Type 1 AGN. The observed Fe K emission radii (R_fe) are determined from
spectrally resolved line widths in X-ray grating spectra, and the dust
sublimation radii (R_dust) are measured either from optical/near-infrared
reverberation time lags or from resolved near-infrared interferometric data.
This direct comparison shows, on an object-by-object basis, that the dust
sublimation radius forms an outer envelope to the bulk of the Fe K emission.
R_fe matches R_dust well in the AGN with the best constrained line widths
currently. In a significant fraction of objects without a clear narrow line
core, R_fe is similar to, or smaller than the radius of the optical broad line
region. These facts place important constraints on the torus geometries for our
sample. Extended tori in which the solid angle of fluorescing gas peaks at well
beyond the dust sublimation radius can be ruled out. We also test for
luminosity scalings of R_fe, finding that Eddington ratio is not a prime driver
in determining the line location in our sample. We discuss in detail potential
caveats due to data analysis and instrumental limitations, simplistic line
modeling, uncertain black hole masses, as well as sample selection, showing
that none of these is likely to bias our core result. The calorimeter on board
Astro-H will soon vastly increase the parameter space over which line
measurements can be made, overcoming many of these limitations.
