The Fe9+ region in active galactic nuclei

Spectroscopic data at resolutions of 1 Å or better, including the Fe Xλ 6374 Å line, are presented for 29 Seyfert and related galaxies. Fe X λ 6374 has certainly or probably been detected in 12 galaxies. The strength of both this line and Fe XI λ 7892 is correlated with that of the Fe VII and O III lines, suggesting the Fe9+ and Fe10+ ions are photoionized. A possible relation between Fe X and Hβ intensities is consistent with this view, although current photoionization models do not agree well with the observed relative intensities of the highly ionized iron lines. Alternatively, the line ratios may be reproduced by collisional ionization in a gas of temperature near 106 K, although a range of temperatures is needed. The probable variability of Fe X λ 6374 in NGC 4151 and the apparent absence of collisional de-excitation limit the radius of the Fe9+ zone to between 1 × 10−4 and 0. 5 pc and its density to between 4 × 104 and 6 × 1011 cm−3. The Fe X and Fe XI lines are blueshifted with respect to the systemic velocity of the galaxy, typically by |120 km s^-1| and are also broader than lines from lower ionization species. We ascribe these effects to a combination of higher outflow/inflow velocities closer to the central source and obscuration.