The shape of broad-line profiles in AGN

TL;DR

This study analyzes broad-line profiles in AGN to determine the dominant velocity components, revealing turbulence and rotation as key broadening mechanisms, with implications for understanding the structure of the broad-line region.

Contribution

Introduces line broadening simulations and compares them with a large AGN dataset to identify turbulence and rotation as primary broadening factors in emission line profiles.

Findings

Broad-line profiles are Lorentzian due to turbulence.

Turbulent velocities vary across emission lines, from 400 km/s to 3,800 km/s.

Rotation broadening dominates the line profile broadening.

Abstract

We present a study of the broad optical/UV emission line profiles in AGN (active galactic nuclei) to get information on the dominant velocity components (turbulence, rotation, etc.) in the central broad-line region (BLR). We introduce line broadening simulations of emission line profiles and compare these results with the largest homogeneous data set of reverberation-mapped AGN. 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 Ha, Hg, Lya, CIII] 1909, He II 1640, and Si IV 1400. The turbulent velocities go from 400 km/s for Hb up to 3,800 km/s for Lya+Nv 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 up to 6,500 km/s. 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.