PHYSICAL CONDITIONS OF THE CORONAL LINE REGION IN SEYFERT-GALAXIES

The launch of the Infrared Space Observatory and new atomic data have opened a window for the study of high-ionization gas in active galacti c nuclei (AGNs). We present the results of a large number of photoioni zation simulations of the ''coronal line'' region in AGNs, employing n ew atomic data from the Opacity and Iron Projects. Our grid of line em ission spans 8 orders of magnitude in gas density and 14 orders of mag nitude in ionizing flux :in an effort to identify the optimal conditio ns in which these lines form. We show that coronal lines form at dista nces from just outside the broad-line region to similar to 400L(43.5)( 1/2) pc, in gas with ionization parameter -2.0 less than or similar to log U(H) less than or similar to 0.75, corresponding to gas densities of 10(2)-10(8.5) cm(-3), With electron temperatures similar to 12,000 -150,000 K. A large range of distances from the central source implies significant line width variation among the coronal lines. We identify several line ratios that could be used to measure relative abundances , and we use these to show that the coronal line gas is likely to be d ust free.