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We present a study of the narrow Fe K$\alpha$ line in seven bright, nearbyAGN that have been observed extensively with the Chandra High EnergyTransmission Grating (HETG). The HETG data reveal a wider Fe K$\alpha$ line inthe first order spectrum than in the second and third order spectra, which weinterpret as the result of spatially extended Fe K$\alpha$ emission. We utilizethese differences in narrow Fe K$\alpha$ line widths in the multi-order ChandraHETG spectra to determine the spatial extent and intrinsic velocity width ofthe emitting material in each object. We find that there is modest evidence forspatially extended emission in each object, corresponding to extension of$r\sim5-100$ pc. These distances are significantly larger than those inferredfrom velocity widths assuming gravitational motions, which give $r\sim0.01-1$pc. This implies that either the gas is emitting at a range of radii, withsmaller radii dominating the velocity width and larger radii dominating thespatial extent, or that the gas is exhibiting non-gravitational motions, whichwe suggest would be outflows due to slight excess redshift in the line andvelocities that exceed the freefall velocity. We also use the spatial extentinformation to estimate the mass of the emitting gas by counting fluorescingiron atoms, finding masses on the order of$M_\mathrm{gas}\sim10^5-10^8\,M_\odot$. Future work with observatories likeXRISM will be able to extend this study to a larger number of AGN and decreaseuncertainties that arise due to the low signal-to-noise of the higher orderHETG data.

astrophysical journal/the astrophysical journal

Probing the Extent of Fe K$\alpha$ Emission in Nearby Active Galactic  Nuclei using Multi-Order Analysis of Chandra High Energy Transmission Grating  Data