Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/ftp/stsci/library/abstracts/1091.abs Дата изменения: Fri Oct 25 22:26:31 1996 Дата индексирования: Sun Dec 23 00:14:57 2007 Кодировка: Поисковые слова: seyfert galaxy

\documentstyle{preprint}

\begin{document}

\title{THE NARROW LINE REGIONS OF SEYFERT AND RADIO GALAXIES}

\author{Andrew S.\ Wilson\\
\\
Space Telescope Science Institute\\
\\
3700 San Martin Drive\\
\\
Baltimore, MD 21218\\
\\
and\\
\\
Astronomy Department\\
\\
University of Maryland\\
\\
College Park, MD 20742}

\pub{{\em proceedings of IAU Colloquium 159,}\\
~\\
Emission Lines in Active Galaxies: New Methods and Techniques,\\
~\\
{\em held 17--20 June 1996 in Shanghai, China}}

\maketitle


\begin{abstract}
This paper reviews the morphology, excitation and ionization of the gas in the
narrow and extended narrow line regions (NLRs and ENLRs) in AGNs. Many high
resolution images of the NLRs of Seyfert galaxies are now available from HST.
In some galaxies, these images reveal straight, sharp-edged V-shaped structures
(believed to be the projections of 3-dimensional cones), while in others
there is a close association between the ionized gas and the radio components.
The latter effect arises through radiative shocks driven into the surrounding
interstellar gas by the outwardly moving radio components or jets.
Photoionization models of ionization-bounded clouds are quite successful in
reproducing the line intensity ratios, but a number of problems remain. These
problems may be resolved if matter-bounded clouds are also present. Differences
between the excitation levels of different NLRs and ENLRs may reflect
variations in the fraction of matter-bounded clouds as well as variations in
the ionization parameter. I discuss the issue of whether the radiation
responsible for photoionizing the gas in Seyfert~2 galaxies originates from a
hidden, compact type~1 Seyfert nucleus or from photoionizing shocks within the
NLR. These two scenarios are hard to distinguish. The photoionizing shock model
requires surprisingly high pre-shock densities, raising the question of whether
the shocks are sufficiently energetic to power the observed line emission.
\end{abstract}

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