INFRARED CORONAL EMISSION-LINES AND THE POSSIBILITY OF THEIR LASER-EMISSION IN SEYFERT NUCLEI

Infrared coronal emission lines are providing a new window for observa tion and analysis of highly ionized gas in such Galactic and extragala ctic sources as Seyfert nuclei and classical novae shells. These lines are expected to be primary coolants in colliding galaxies, galaxy clu ster cooling flows, cometary-compact H II regions, and supernova remna nts. In this paper, we compile a complete list of infrared (lambda > 1 mum) lines due to transitions within the ground configurations 2s(2)2 p(k) and 3s(2)3p(k) (k = 1-5) or the first excited configurations 2s2p and 3s3p of highly ionized (chi greater-than-or-equal-to 100 eV) astr ophysically abundant [n(X)/n(H) greater-than-or-equal-to 10(-6)]elemen ts. Included are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of approximately 1-280 mum. We present results from detailed balance calculations, cri tical densities for collisional deexcitation, intrinsic photon rates, branching ratios, and excitation temperatures for the majority of the compiled transitions. The temperature and density parameter space for dominant cooling via infrared coronal lines is presented, and the rela tionship of infrared and optical coronal lines is discussed. We find t hat under physical conditions found in Seyfert nuclei, 14 of 70 transi tions examined have significant population inversions in levels that g ive rise to infrared coronal lines. Laser gain lengths and correspondi ng column densities are calculated for dense [10(6) less-than-or-equal -to n(e) (cm-3) less-than-or-equal-to 10(9)] collisionally ionized pla smas. Application of these results to cooler plasmas photoionized by p ower-law continuum radiation fields is also discussed. We find that se veral infrared coronal line transitions have laser gain lengths that c orrespond to column densities of 10(24-25) cm-2 which are modeled to e xist in Seyfert nuclei. Observations that can reveal inverted level po pulations and laser gain in infrared coronal lines are also suggested.