Bowshocks and the formation of the narrow-line region of Seyfert galaxies.
Abstract
Considerable evidence exists for a relationship between the optical narrow-line region (the NLR) and the nuclear non-thermal radio emission in Seyfert galaxies. In a previous paper we introduced a model for the NLR, which we here develop and describe more fully, in which the linear motions of the radio components drive bowshocks into the ambient nuclear medium. The cooled shocked gas, photoionized by the UV nuclear continuum, produces the optical NLR emission. The radio components may take the form of bubbles of plasma ejected from the nucleus, or may represent the working surfaces of jets. We calculate [O III] λ5007 luminosities from our model of around 10^39^ - 10^42^ erg s^-~1^, which is in good agreement with the observed NLR [O III] λ5007 luminosity range. The emission lines produced by the model have widths of up to ~500 km s^-1^ and may have large asymmetries. The angle of motion of the bowshock to the line of sight is the most important single parameter governing the shape and width of the profiles. The width of each profile is, in general, considerably less than the velocity of the bowshock generating it. The model can explain the wide diversity of observed NLR line profile shapes, the predominance of profiles with excess emission in the blue wing, and the association between the radio and optical structures, including displacements between the centres of radio and optical emission.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 1992
- DOI:
- 10.1093/mnras/255.2.351
- Bibcode:
- 1992MNRAS.255..351T
- Keywords:
-
- Astronomical Spectroscopy;
- Bow Waves;
- Radio Emission;
- Seyfert Galaxies;
- Shock Waves;
- Emission Spectra;
- Galactic Nuclei;
- Line Spectra;
- Nonthermal Radiation;
- Astrophysics