Line and continuum emission from the outer regions of accretion discsin active galactic nuclei. IV. Line emission.

Following the two previous papers where we have discussed the radial structure of the outer regions of accretion discs in Active Galactic Nuclei and studied the influence of a non-thermal source of radiation on the disc structure, we compute the line emission of the accretion disc. We use the results of a grid of photoionisation models obtained in a previous paper to get the line flux emitted at each radius of the disc. We obtain integrated line intensities and line profiles for given disc physical parameters (bolometric luminosity and ratio of the bolometric luminosity to the Eddington luminosity, inclination angle and disc radius) and for a given illumination model (compact source, or scattered radiation). We show that the disc should emit a line spectrum, especially if its radius is large (>~ 10^4^ gravitational radii). This spectrum consists mainly of Low Ionization Lines, and can be a major part of the Broad Line emission. An important conclusion is that line ratios do not depend on the luminosity and depend weakly on the illumination model. This result could explain the remarkable similarity of line spectra in quasars and Seyfert galaxies. One unexpected result is that the profiles are generally not double peaked, except if the radius of the disc is small. The profiles of the lines differ from each others, the Hβ profile being the broadest and Mg II the narrowest.