Profiles of emission lines in AGN – II. Analysis of a sample of [O III] profiles

Abstract

Statistical analysis of a sample of active galactic nuclei (AGN) [O III]λ5007 high-resolution (FWHMS ≲ 130 km s−1) line profiles, complemented with other observational information, showed that line kurtosis correlates with narrow-line Balmer decrement, indicating that there is dust inside the narrow-line region. The dust affects preferentially the low-velocity emitting regions. Line kurtosis depends also on radio luminosity and presence of a broad-line region. The analysis shows a correlation between line FWHM and host galaxy inclination, pointing to the planar and aligned nature of the narrow-line region velocity field. Radio-quiet objects showed a good correlation between line FWHM and optical/radio luminosity. No correlation was found on the radio-loud ones, indicating that probably different mechanisms are at play in these two classes of objects. Late-type spirals showed, on the mean, lines with narrower FWHM than early-type ones. The effect is measurable, however, only on the low-velocity emitting regions, indicating that the velocity field in these regions may be shaped by the galaxy-bulge gravitational field. Line asymmetry does not appear to be a good diagnostic tool for probing the velocity field. About 23 per cent of the radio-quiet objects showed lines with red asymmetry.