The shape of broad-line profiles in active galactic nuclei

Abstract

Aims. We present a study of the broad optical/UV emission line profiles in active galactic nuclei (AGN) to get information on the dominant velocity components (turbulence, rotation, etc.) in the central broad-line region (BLR). Methods. We introduce line broadening simulations of emission line profiles and compare these results with the largest homogeneous data set of reverberation-mapped AGN. Results. The underlying broad-line profiles in AGN are Lorentzian profiles caused by turbulence in the line emitting region. The turbulent velocities are different for the different line emitting regions of Hγ, Hα, Lyα, C iii] λ1909, He ii λ1640, and Si iv λ1400. The turbulent velocities go from 400 km s-1 for Hβ up to 3800 km s-1 for Lyα + N v λ1240. The dominating broadening mechanism of these profiles is broadening due to rotation. The rotation velocities causing the line profile broadening go from 500 km s-1 up to 6500 km s-1. Here we present interrelations between observed emission line widths (FWHM) and their related rotational velocities to correct for the contribution of the turbulence to the broad-line profiles. © 2013 ESO.