Dynamics of the Lyα and C IV Emitting Gas in 3C 273

Abstract

In this paper we study the variability properties of the Lyα and C IV emission lines in 3C 273 using archival International Ultraviolet Explorer observations. Our data show for the first time the existence of variability on timescales of several years. We study the spatial distribution and the velocity field of the emitting gas by performing detailed analyses on the line variability using correlations, one- and two-dimensional response functions, and principal component analysis. In both lines we find evidence for two components, one that has the dynamic properties of gas in Keplerian motion around a black hole with a mass on the order of 10⁹ M_solar, and one that is characterized by high, blueshifted velocities at large lag. There is no indication of the presence of optically thick emission medium in either the Lyα or C IV response functions. The component characterized by blueshifted velocities, which is comparatively much stronger in C IV than in Lyα, is more or less compatible with being the result of gas falling toward the central black hole with free-fall acceleration. We propose, however, that the line emission at high, blueshifted velocities is better explained in terms of entrainment of gas clouds by the jet. Therefore, this gas is probably collisionally excited as a result of heating due to the intense infrared radiation from the jet, which would explain the strength of this component in C IV relative to Lyα. This phenomenon might be a signature of disk-jet interaction.