X-RAY LINES IN ACTIVE GALACTIC NUCLEI AND PHOTOIONIZED GASES

摘要

This paper addresses the observed 0.1-10 keV spectrum in active galactic nuclei (AGNs) and other photoionized gases. Detailed calculations, encompassing a large range in density (10-40~(14) cm~(-3)), column density (10~(21)-10~(23.5) cm~(-2)), and level of ionization (3 orders of magnitude in ionization parameter), are described and discussed. The results are presented as line intensity and three types of equivalent width over the entire range of physical conditions. We identify the most likely conditions in the X-ray-absorbing gas in AGNs and argue that its temperature is below 2 x 10~5 K and that it is thermally stable. The strongest 0.1-10 keV lines, when observed against the central source continuum, have typical equivalent widths of 5-50 eV and are thus at the limit of present-day detection. The equivalent width can be significantly stronger when the line is observed against the absorbed continuum. Much larger equivalent widths, of 100-1000 eV, are expected when the central continuum is obscured, as in Seyfert 2 galaxies. The importance of line-continuum fluorescence diminishes with line optical depth, and we do not find this process to be important in warm AGN absorbers. The X-ray line intensities depend on the gas density, especially for very low (N < 10~3 cm~(-3)) and very high (N > 10~(12) cm~(-3)) densities. They are also sensitive to the geometry and covering fraction.