EDP Sciences
Free Access
Volume 371, Number 2, May IV 2001
Page(s) 507 - 511
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20010404

A&A 371, 507-511 (2001)
DOI: 10.1051/0004-6361:20010404

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

S. Komossa

Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

(Received 9 February 2001 / Accepted 16 March 2001)

NGC 4151 is one of the brightest and best-studied Seyfert galaxies. Here, we present a two-phase model of the narrow-line region (NLR) of NGC 4151. This study is motivated by (i) the fact that the X-ray spectrum of NGC 4151 is among the flattest known for Seyferts, and (ii) the recent Chandra detection of an X-ray narrow-line region in this galaxy. X-ray spectra as flat as that of NGC 4151 ( $\Gamma_{\rm x}$ $\simeq -1.5$) are expected to favor the presence of two gas phases in pressure equilibrium (Krolik et al. 1981). In the present study, we show that a pronounced two-phase equilibrium develops in the extended emission-line region if we use the observed multi-wavelength spectrum of NGC 4151 to ionize the clouds. The material is stable to isobaric perturbations over a wide range of temperatures. We therefore propose that such a condition has arisen in the NLR of NGC 4151, and that it explains the detection of hot, extended X-ray gas which we identify as the NLR-cloud confining medium.

Key words: galaxies: Seyfert -- galaxies: individual: NGC 4151 -- galaxies: nuclei -- galaxies: emission lines -- X-rays: galaxies

Offprint request: S. Komossa, skomossa@xray.mpe.mpg.de

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