Integral Field Spectroscopy of the Central Regions of 3C 120: Evidence of a Past Merging Event

Optical integral field spectroscopy (IFS), combined with Hubble Space Telescope (HST) WFPC imaging, was used to characterize the central regions of the Seyfert 1 radio galaxy 3C 120. We carried out the analysis of the data, deriving intensity maps of different emission lines and the continua at different wavelengths from the observed spectra. Applying a two-dimensional modeling to the HST images, we decoupled the nucleus and the host galaxy and analyzed the host morphology. The host is a highly distorted bulge-dominated galaxy, rich in substructures. We developed a new technique to model the IFS data extending the two-dimensional modeling (hereafter three-dimensional modeling). Using this technique, we separated the Seyfert nucleus and the host galaxy spectra and derived a residual data cube with spectral and spatial information of the different structures in 3C 120. Three continuum-dominated structures (named A, B, and C) and three other extended emission-line regions (EELRs, named E sub(1), E sub(2), and E sub(3)) are found in 3C 120, which does not follow the general behavior of a bulge-dominated galaxy. We also found shells in the central kiloparsec that may be remnants of a past merging event in this galaxy. The origin of E sub(1) is most probably due to the interaction of the radio jet of 3C 120 with the intergalactic medium (Axon et al. 1989; Sanchez et al. 2004a). Structures A, B, and the shell at the southeast of the nucleus seem to correspond to a larger morphological clumpy structure that may be a tidal tail, a consequence of the past merging event. We found a bright EELR (E sub(2)) in the innermost part of this tidal tail, nearby the nucleus, which shows a high ionization level. The kinematics of the E sub(2) region and its connection to the tidal tail suggest that the tail has channeled gas from the outer regions to the center.