Orientation and Evolutionary Effects in Active Galactic Nuclei

Charlene A. Heisler, PASA, 15 (2), 167
The html and gzipped postscript versions of this paper are in preprint form.
To access the final published version, download the pdf file
.

Next Section: Dusty Tori in Seyfert
Title/Abstract Page: Orientation and Evolutionary Effects
Previous Section: Orientation and Evolutionary Effects
Contents Page: Volume 15, Number 2

Introduction

Active Galactic Nuclei (=AGN) are thought to be powered by the accretion of gas onto a central massive black hole. The most common type of nearby AGN are Seyfert galaxies, named after Carl Seyfert (1943), who isolated and studied several galaxies with bright nuclei and relatively high-ionisation emission lines in their spectra, which were broader than the lower-ionisation emission lines observed in ``normal" galaxies. Seyfert galaxies are separated into two classes based on their emission line widths (eg. Khachikian & Weedman 1974, Osterbrock 1989). Seyfert 1 galaxies exhibit broad emission lines that are attributed to ionized gas within 1 pc of the central massive black hole, whereas the spectra of Seyfert 2 galaxies only show narrower emission lines, believed to originate from a much larger region around the core. The standard model of AGN holds that a central engine (presumed to be accretion onto a super massive black hole) photoionises clouds within a parsec to produce observed broad lines observed in Seyfert 1 galaxies. Based on reverberation mapping, the spatial extent of the broad line emission is of the order of a few light-days to light-weeks (eg. Peterson 1993), while narrow band imaging has clearly shown that the narrow line emission extends to tex2html_wrap_inline500kpc (eg. Pogge 1989; Mulchaey, Wilson & Tsvetanov 1996) The currently favored paradigm for the unification of Seyfert galaxies, asserts that the central engine is surrounded by a dusty torus which obscures our view of the broad line region directly if viewed edge-on resulting in the classification of a Seyfert 2 (eg. Antonucci 1993, Urry & Padovani 1995).


Next Section: Dusty Tori in Seyfert
Title/Abstract Page: Orientation and Evolutionary Effects
Previous Section: Orientation and Evolutionary Effects
Contents Page: Volume 15, Number 2

Welcome... About Electronic PASA... Instructions to Authors
ASA Home Page... CSIRO Publishing PASA
Browse Articles HOME Search Articles
© Copyright Astronomical Society of Australia 1997
ASKAP
Public