A two-phase model for the narrow line region of NGC 4151

NGC 4151 is one of the brightest and best-studied Seyfert galaxies. Here, w e present a two-phase model of the narrow-line region (NLR) of NGC 4151. Th is study is motivated by (i) the fact that the X-ray spectrum of NGC 4151 i s among the attest known for Seyferts, and (ii) the recent Chandra detectio n of an X-ray narrow-line region in this galaxy. X-ray spectra as at as tha t of NGC 4151 (Gamma (x) similar or equal to -1.5) are expected to favor th e presence of two gas phases in pressure equilibrium (Krolik et al. 1981). In the present study, we show that a pronounced two-phase equilibrium devel ops in the extended emission-line region if we use the observed multi-wavel ength spectrum of NGC 4151 to ionize the clouds. The material is stable to isobaric perturbations over a wide range of temperatures. We therefore prop ose that such a condition has arisen in the NLR of NGC 4151, and that it ex plains the detection of hot, extended X-ray gas which we identify as the NL R-cloud confining medium.