Soft X‐Ray Absorption by Fe0+to Fe15+in Active Galactic Nuclei

A full set of calculations is presented for inner-shell n = 2 to 3photoexcitation of the 16 iron charge states: Fe I through Fe XVI. The blend ofthe numerous absorption lines arising from these excitations (mainly 2p - 3d)forms an unresolved transition array (UTA), which has been recently identifiedas a prominent feature between 16 - 17 \AA in the soft X-ray spectra of activegalactic nuclei (AGN). Despite the blending within charge-states, the ampleseparation between the individual-ion features enables precise diagnostics ofthe ionization range in the absorbing medium. Column density and turbulentvelocity diagnostics are also possible, albeit to a lesser accuracy. Anabbreviated set of atomic parameters useful for modeling the Fe 2p - 3d UTA isgiven. It is shown that the effects of accompanying photoexcitation to higherlevels ($n \ge$ 4), as well as the associated photoionization edges, may alsobe relevant to AGN spectra.Comment: Accepted for publication in The Astrophysical Journa