Analysis of the broad emission line profiles in the active galactic nucleus 3C 390.3

Abstract

We present a study of ultraviolet and optical spectra of the active galaxy 3C 390.3 taken as part of the International Active Galactic Nuclei (AGNs) Watch during the period January 1995–January 1996. We have measured the C IV-to-Lyα and Lyα-to-Hβ ratios at different velocities in the line profiles. We find that the Lyα-to-Hβ ratio varies across the line profiles. The ratio is high in the low-velocity centre of the lines at all times but decreases in the high-velocity wings. The C IV-to-Lyα line ratio, however, is low at the line centre but becomes higher in the wings. This velocity dependence of line ratios is different from what has been reported for most other AGNs. Theoretical modelling of the C IV-to-Lyα and Lyα-to-Hβ ratios, using the photoionization code CLOUDY, suggests that the density is higher in the higher-velocity gas producing the displaced broad line peaks, and that the observed line ratios can be accounted for by two systems of clouds. One corresponds to a high ionization line zone with an ...