Radiation pressure on dust explains the Low Ionized Broad Emission Lines in Active Galactic Nuclei

Abstract

Broad emission lines are the most characteristic features in the spectra of active galaxies. They mostly show either a single-peaked or double-peaked profiles; and originate from a complex dynamics of the likely discrete clouds moving in a spatially extended region so-called Broad Line Region (BLR). We follow a non-hydrodynamical single-cloud approach to the BLR dynamics based on the dust-driving model of Czerny & Hryniewicz. We previously showed in details that the 2.5D version of the model could provide us with the 3D geometry of the BLR. In this paper, we provide a large grid of results based on which we aim at testing the model with calculation of the spectral line generic profiles. We show that the shape of profiles not only depends on the accretion rate of the source, the black hole mass, and the viewing angle, but also it is most significantly affected by the adopted dust-to-gas mass ratio that regulates the strength of the radiation pressure. We also show that the model can appropriately explain the low ionized broad emission lines of the mean spectrum of quasars, such as MgII and Hbeta.