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

W Kollatschny,K Ulbrich,M Zetzl,S Kaspi,M Haas

doi:10.1051/0004-6361/201423901

Abstract

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.

Highlights

The variable radio source 3C 120 has been identified to be a distant Seyfert 1 galaxy of redshift 0.0334 by Burbidge (1967) as early as 1967
We demonstrated in recent papers (Kollatschny & Zetzl 2011, 2013a,b,c) that we are able to make statements about the broad-line region (BLR) structure in active galactic nuclei (AGN) based on variability studies in combination with line profile studies
The faster response of the line wings is explained by accretion disk models for the line-emitting regions (e.g. Perez et al 1992, or Welsh & Horne 1991)

Summary

Introduction

The variable radio source 3C 120 has been identified to be a distant Seyfert 1 galaxy of redshift 0.0334 by Burbidge (1967) as early as 1967. Peterson et al (1998) carried out a spectral variability campaign of 3C 120 during a period of eight years from 1989 to 1996. They derived a delay of τ = 44.+−2280.. Days of the integrated Hβ emission line with respect to the variable continuum flux. The value of this delay – that is the distance of the lineemitting region from the central ionizing source – had a large. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, the LudwigMaximilians-Universität München, and the Georg-August-Universität Göttingen

Results

Discussion

Conclusion