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 electron density, Ne ≈ 1010-108 cm−3. It is presumably located above the accretion disc. The other system corresponds to a low-ionization line zone which, because of the line profiles, is probably part of the accretion disc, and which has a higher electron density, Ne ≈ 1011-1012 cm−3. We discuss the possible geometry of the broad-line-region in 3C 390.3.
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Active galaxy 3C 390.3;
C IV-to-Lyα ratio;
Emission line profiles;
Document Type: Research Article
Euro-Asian Astronomical Society Universitetskij Prospekt 13 Moscow 119899 Russia
Sternberg Astronomical Institute Universitetskij Prospekt 13 Moscow 119899 Russia
Department of Physics and Astronomy University of Nebraska Lincoln Nebraska 68588-0111 USA
Publication date: 2004-08-01
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