Dynamics of the Lyα and CivEmitting Gas in 3C 273

In this paper we study the variability properties of the Lyman alpha and C IVemission lines in 3C273 using archival IUE observations. Our data show for thefirst time the existence of variability on time scales of several years. Westudy the spatial distribution and the velocity field of the emitting gas byperforming detailed analyses on the line variability using correlations, 1D and2D response functions, and principal component analysis. In both lines we findevidence for two components, one which has the dynamic properties of gas inKeplerian motion around a black hole with a mass of the order of 10^9 Mo, andone which is characterized by high, blue-shifted velocities at large lag. Thereis no indication of the presence of optically thick emission medium neither inthe Lya, nor in the Civ response functions. The component characterized byblue-shifted velocities, which is comparatively much stronger in Civ than inLya, is more or less compatible with being the result of gas falling towardsthe central black hole with free-fall acceleration. We propose however that theline emission at high, blue-shifted velocities is better explained in terms ofentrainment of gas clouds by the jet. This gas is therefore probablycollisionally excited as a result of heating due to the intense infraredradiation from the jet, which would explain the strength of this component inCiv relative to Lya. This phenomenon might be a signature of disk-jetinteraction.Comment: 16 pages, 10 figures. Accepted for publication in ApJ. Uses aaste