Broad-line region structure and kinematics in the radio galaxy 3C 120

Abstract

Context. Broad emission lines originate in the surroundings of supermassive black holes in the centers of active galactic nuclei (AGN). These broad-line emitting regions are spatially unresolved even for the nearest AGN. The origin and geometry of broad-line region (BLR) gas and their connection with geometrically thin or thick accretion disks is of fundamental importance for the understanding of AGN activity. Aims. 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. Methods. We took spectra with a high signal-to-noise ratio of 3C 120 with the 9.2 m 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. Results. 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 Hα and Hβ 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 He ii λ4686 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.

The Structure of the Broad-line Region in Active Galactic Nuclei. II. Dynamical Modeling of Data From the AGN10 Reverberation Mapping Campaign

“…The radial distribution of Hβ emission in 3C 120 has a Gamma distribution shape parameter that is close to exponential. We obtain a mean and median time delay consistent to within the uncertainties with the values reported by G12 as well as recent work by Kollatschny et al (2014), who report τ Hβ = 27.9 +7.1 −5.9 days. The kinematics of 3C 120 are inferred to be a combination of near-circular elliptical orbits and inflow on mostly radial orbits.…”

“…Kollatschny et al (2014) also performed a velocityresolved analysis of 3C 120 RM data from a separate campaign and found similar features. The velocity-binned mean time delays shown in Figure 4 are also consistent with those measured in Paper I, though the measurements made directly from the spectra (red) deviate somewhat from the model (blue) in the second-bluest wavelength bin.…”

Modelling photometric reverberation data: a disk-like broad-line region and a potentially larger black hole mass for 3C 120

“…By modelling detailed spectroscopic reverberation mapping and velocity-delay maps of 3C 120, albeit with softer light curve features than seen in our data, Grier et al (2013) and Kollatschny et al (2014) also found evidence for a disk-like BLR, but did not specify the parameters. Remarkably, our results were obtained without explicit velocity information, but under the assumption that the BLR is essentially virialised.…”

“…The source 3C 120 has been monitored spectroscopically -assisted by BB photometry -in 2008/2009 by Kollatschny et al (2014 and in 2010/2011 similarly by Grier et al (2012Grier et al ( , 2013. The data by G+2013 are very well sampled, but catch only rather smooth variations in the light curves.…”

“…In both studies evidence for a disk-like BLR geometry was found. The broad-line radio galaxy 3C 120 has been observed with velocity-resolved RM at two different epochs (Grier et al 2012 andKollatschny et al 2014). Below we discuss details of this when we compare their results with our data (Sect.…”