High resolution line profiles in the Seyfert galaxy NGC 3783: The structure of the emitting regions

• Published in: Monthly notices of the Royal Astronomical Society 1981-08, Vol.195 (4), p.787-804
• Main Authors: Pelat, Didier, Alloin, Danielle, Fosbury, Robert A. E.
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/195.4.787

We present the analysis of emission line profiles in the Seyfert nucleus of NGC 3783. The lines, covering a wide range of ionization from O0 up to Fe9+, are analysed from IPCS or electronographic data obtained with resolutions from 0.03 to 0.12 nm. When the signal-to-noise ratio allowed it, a precise analysis generally showed a broad, blueshifted component in the line under consideration. The main results of this study are the following: (1) There appears to be a relationship between the FWHI of the main component within a line and the ionization potential of the corresponding ion. (2) For all the forbidden lines, there is a relationship between the FWHI of any component and its emission shift, with broad components and high ionization species being more blueshifted: for example, the main broad component in the [Fe X] line is blueshifted by 400 km s−1 with respect to the [O I], [O II] and [N II] emission velocity. (3) The Balmer lines show components corresponding to these forbidden line regions but their main contribution is from a very broad (3000 km s−1) redshifted (+ 200 km s−1) component. The results are most plausibly interpreted in the framework of a central massive object surrounded by an accretion disc (AD), for which we derive an inclination of 15° and a mean radius of 103RS. Arguments are then presented that only the high-density region ($N_\text e\gt 10^{10} \text {cm}^{-3}$) is concerned with the AD itself, while the forbidden-line region is dominated by a radial rather than a rotational velocity field whose magnitude increases towards the centre where the photo-ionizing source lies. Consideration of the ionization equilibrium together with the observed radial velocities, assumed to be from infalling matter, favour the picture of filaments clustering towards the centre and decelerated by frictional mechanisms which also increase the turbulence of the medium.