Kinematics of the Broad-line Region of 3C 273 from a 10 yr Reverberation Mapping Campaign

Abstract

Despite many decades of study, the kinematics of the broad-line region of 3C 273 are still poorly understood. We report a new, high signal-to-noise, reverberation mapping campaign carried out from 2008 November to 2018 March that allows the determination of time lags between emission lines and the variable continuum with high precision. The time lag of variations in H β relative to those of the 5100 Å continuum is days in the rest frame, which agrees very well with the Paschen- α region measured by the GRAVITY at The Very Large Telescope Interferometer. The time lag of the H γ emission line is found to be nearly the same as that for H β . The lag of the Fe ii emission is days, longer by a factor of ∼2 than that of the Balmer lines. The velocity-resolved lag measurements of the H β line show a complex structure that can be possibly explained by a rotation-dominated disk with some inflowing radial velocity in the H β -emitting region. Taking the virial factor of f BLR  = 1.3, we derive a BH mass of and an accretion rate of from the H β line. The decomposition of its Hubble Space Telescope images yields a host stellar mass of , and a ratio of in agreement with the Magorrian relation. In the near future, it is expected to compare the geometrically thick BLR discovered by the GRAVITY in 3C 273 with its spatially resolved torus in order to understand the potential connection between the BLR and the torus.