Fe–K LINE PROBING OF MATERIAL AROUND THE ACTIVE GALACTIC NUCLEUS CENTRAL ENGINE WITH SUZAKU

We systematically analyzed the high-quality Suzaku data of 88 Seyfert galaxies, about 31% of which are Compton-thick active galactic nuclei (AGNs). We obtained a clear relation between the absorption column density and the equivalent width (EW) of the 6.4 keV line above 1023 cm−2, suggesting a wide-ranging column density of 1023–1024.5 cm−2 with a similar solid and an Fe abundance of 0.7–1.3 solar for Seyfert 2 galaxies. The EWs of the 6.4 keV line for Seyfert 1 galaxies are typically 40–120 eV, suggesting the existence of Compton-thick matter like the torus with a column density of >1023 cm−2 and a solid angle of (0.15–0.4) × 4π, and no difference of neutral matter is visible between Seyfert 1 and 2 galaxies. An absorber with a lower column density of 1021–1023 cm−2 for Compton-thin Seyfert 2 galaxies is suggested to be not a torus but an interstellar medium. These constraints can be understood by the fact that the 6.4 keV line intensity ratio against the 10–50 keV flux is almost identical within a range of 2–3 in many Seyfert galaxies. Interestingly, objects exist with a low EW, 10–30 eV, of the 6.4 keV line, suggesting that those torus subtends only a small solid angle of <0.2 × 4π. Thanks to high-quality data with a good signal-to-noise ratio and the accurate continuum determination of Suzaku, ionized Fe–Kα emission or absorption lines are detected from several percent of AGNs. Considering the ionization state and EW, emitters and absorbers of ionized Fe–K lines can be explained by the same origin, and highly ionized matter is located at the broad-line region. The rapid increase in EW of the ionized Fe–K emission lines at NH>1023 cm−2 indicates that the column density of the ionized material also increases together with that of the cold material. It is found that these features seem to change for brighter objects with more than several 1044 erg s−1 such that the Fe–K line features become weak. This extends the previously known X-ray Baldwin effect on the neutral Fe–Kα line to ionized emission or absorption lines. The luminosity dependence of these properties, regardless of the scatter of black hole mass by two orders of magnitudes, indicates that the ionized material is associated with the structure of the parent galaxy rather than the outflow from the nucleus.

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