Broad emission lines originate in the surroundings of supermassive black
holes in the centers of active galactic nuclei (AGN). One method to investigate
the extent, structure, and kinematics of the BLR is to study the continuum and
line profile variability in AGN. We selected the radio-loud Seyfert 1 galaxy 3C
120 as a target for this study. We took spectra with a high signal-to-noise
ratio of 3C 120 with the 9.2m Hobby-Eberly Telescope between Sept. 2008 and
March 2009. In parallel, we photometrically monitored the continuum flux at the
Wise observatory. We analyzed the continuum and line profile variations in
detail (1D and 2D reverberation mapping) and modeled the geometry of the
line-emitting regions based on the line profiles. We show that the BLR in 3C
120 is stratified with respect to the distance of the line-emitting regions
from the center with respect to the line widths (FWHM) of the rms profiles and
with respect to the variability amplitude of the emission lines. The emission
line wings of H{\alpha} and H{\beta} respond much faster than their central
region. This is explained by accretion disk models. In addition, these lines
show a stronger response in the red wings. However, the velocity-delay maps of
the helium lines show a stronger response in the blue wing. Furthermore, the
HeII{\lambda}4686 line responds faster in the blue wing in contradiction to
observations made one and a half years later when the galaxy was in a lower
state. The faster response in the blue wing is an indication for central
outflow motions when this galaxy was in a bright state during our observations.
The vertical BLR structure in 3C 120 coincides with that of other AGN. We
confirm the general trend: the emission lines of narrow line AGN originate at
larger distances from the midplane than AGN with broader emission lines.Comment: 18 pages, 25 figures, Astronomy & Astrophysics in pres
