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 H gamma, H alpha, Ly alpha, C III] lambda 1909, He II lambda 1640, and Si IV lambda 1400. The turbulent velocities go from 400 km s(-1) for H beta up to 3800 km s(-1) for Ly alpha + N V lambda 1240. 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.