Vertical broad-line region structure in nearby active galactic nuclei

Institut für Astrophysik, Universität Göttingen, Friedrich-Hund Platz 1, 37077 Göttingen, Germany
e-mail: wkollat@astro.physik.uni-goettingen.de

Received: 11 April 2013
Accepted: 16 July 2013

Abstract

Context. Broad emission lines are emitted in the surroundings of supermassive black holes in the centers of active galactic nuclei (AGN). This region is spatially not resolved.

Aims. We intend to get information on the structure and geometry of this broad emitting line region based on line profile observations.

Methods. We model the rotational and turbulent velocities in the line-emitting regions based on observed full-width at half maximum line values (FWHM) and σ_line of the variable broad emission lines in four nearby AGN: NGC 3783, NGC 7469, NGC 5548, and 3C 390.3. On the basis of these velocities, we estimate the height of the line-emitting regions above the midplane in context with their distances from the center.

Results. The Hβ lines are emitted in a more flattened configuration above the midplane in comparison to the highly ionized lines. The Hβ lines originate at heights of 0.7 to 1.6 light-days and at distances of 1.4 to 24 light-days with height/distance ratios (H/R) of only 0.07 to 0.5. The highly ionized lines originate at smaller radii than the Hβ lines and/or at greater distances above the midplane with H/R values of 0.2 to 1.7. In total, the emission lines do not originate in a thin atmosphere of an accretion disk but rather at very extended regions above an accretion disk. The observed geometries of the line-emitting regions resemble the geometries of accretion disk wind models. Furthermore, the angle of the central opening cone (generated by the emitting regions of the highly ionized lines) is small for those galaxies with slow rotational velocities and increases with the rotation velocity of the central region.

Conclusions. The derived geometries of the line-emitting regions of all four AGN are consistent with the geometries that are predicted in outflowing disk wind models.