2019MNRAS.484.3180P

We investigate the structure of the Mg II broad line emission region in a sample of 284 Type 1 active galactic nuclei (AGNs), through comparing the kinematical parameters of the broad Mg II and broad Hβ lines. We found that the Mg II emitting region has more complex kinematics than the Hβ one. It seems that the Mg II broad line originates from two subregions: one which contributes to the line core, which is probably virialized, and the other, 'fountain-like' emitting region, with outflows-inflows nearly orthogonal to the disc, which become suppressed with stronger gravitational influence. This subregion mostly contributes to the emission of the Mg II broad line wings. The kinematics of the Mg II core emitting region is similar to that of the Hβ broad line region (seems to be virialized), and therefore the Full Width at Half-Maximum (FWHM) of Mg II still can be used for the black hole (BH) mass estimation in the case where the Mg II core component is dominant. However, one should be careful with using the Mg II broad line for the BH mass estimation in the case of very large widths (FWHM > 6000 km s^–1) and/or in the case of strong blue asymmetry.